WO2008001092A2

WO2008001092A2 - Radar for through wall detection

Info

Publication number: WO2008001092A2
Application number: PCT/GB2007/002416
Authority: WO
Inventors: Michael Hugh Burchett; Per Arne Vincent Utsi; Goron Kenneth Andrew Oswald; Edwin Christopher Carter; Jonathan Peter Edgcombe; Gary Kemp; Robert John Carter
Original assignee: Cambridge Consultants Limited
Priority date: 2006-06-28
Filing date: 2007-06-28
Publication date: 2008-01-03
Also published as: WO2008001092A3

Abstract

Radar apparatus for detecting an object in through wall and related applications, the radar apparatus comprising a transmitter for transmitting radar signals, and a receiver for receiving reflected portions of said transmitted signals from said object. The radar apparatus is configured for operation in any of at least a first and a second selectable mode. The transmitter is configured for transmitting radar signals in accordance with a selected one of the modes of operation, and said receiver is configured for receiving said reflected portions of said signals transmitted in accordance with said selected mode of operation. The radar apparatus is configured for transmission of signals, through an obstacle, to said object when operating in at least one of said modes.

Description

Radar

This invention relates to radar apparatus. In particular, this invention relates to a radar apparatus for use in through wall and related applications. This invention extends to methods of operating radar apparatus and to radar systems. Radar systems are generally concerned with objects moving at a macroscopic level, for example, aircraft, marine vessels, terrestrial vehicles or the like. It will be appreciated that the term 'macroscopic' in this context refers generally to motion of magnitude of at least half the wavelength (λ/2) at the frequency of interest and more typically to motion of magnitude significantly greater than the wavelength. Objects identified as being substantially stationary (such as buildings), slow moving (such as the sea), and/or oscillatory (such as trees moving in the wind) are generally discriminated against because targets moving at a greater velocity are perceived to represent a greater threat. Such systems typically approximate a detected object as being a single inflexible object.

In reality, objects often include a certain amount of flexibility and have components which move, vibrate, or otherwise fluctuate relative to the motion (or lack of motion) of the rest of the object.

Fluctuating components of an object detected by a radar system may, for example, include flexing and vibration of an object's body and/or moving parts on the object such as scanning antennas, rotating wheels, propulsion systems, moving or vibrating machinery (for example weapons systems), and even human personnel. The fluctuating components may be internal or external and may be fully or partially obscured by intermediate obstacles such as walls, trees, bushes or the like.

In some applications, for example through wall site monitoring or the like, the target objects of interest may be human beings having external fluctuating components associated with breathing, speech, and limb movements, and internal fluctuations associated with for example a heart beat. In such applications, however, the objects are obscured by the wall of the building (or the like) being monitored. Furthermore, if the target objects (i.e. humans) are not moving around the site (e.g. sitting at a desk, injured, hiding, or the like) detection is difficult because there are no associated Doppler variations associated to detect.

Furthermore, in through wall site monitoring applications the capability to detect an object, and to obtain accurate information (e.g. positional information) about it, is very dependent on the position of the object within the building, especially where there are additional internal walls, and/or other obstacles obscuring the object.

Macroscopic movement of an object relative to a detection system gives rise to Doppler frequency shifts, usually over several wavelengths of the frequency of interest received radar return signal. These shifts may be extracted and analysed to identify a moving object, to determine its velocity and, where the Doppler shift is changing, to identify the objects acceleration. Doppler shifts may be extracted, for example, by analysis of associated changes in phase of the received return signal. Fluctuations associated with smaller variations in motion (typically less than a quarter of the wavelength (λ/4)) give rise to higher order effects also known as micro-Doppler effects.

Where a radar system is purely concerned with identifying, classifying and extracting positional information about an object moving at a macroscopic level, the higher order effects can be seen as undesirable discrepancies in the resulting processed data. The effects may, for example, result in artefacts in imaging data due to differences between the imaging model used and the actual processed data.

There are many applications (such as through wall site monitoring or the like) in which remote derivation of information about relatively small variations in the motion of an object, or a component of an object, would be particularly beneficial. The derivation of information from such small Doppler effects is, however, difficult because the variations of interest represent such small changes of the received signal.

Accordingly the present invention seeks to provide improved radar apparatus, radar systems, and methods of operating such apparatus and systems. Multimode operation

According to one aspect of the invention, there is provided a radar for use in through wall and related applications, the radar comprising means for transmitting radar signals in accordance with a first mode of operation, means for receiving reflected radar signals transmitted using the first operating mode, means for transmitting radar signals in accordance with a second mode of operation, means for receiving reflected radar signals transmitted using the second operating mode, and means for switching between the first and second operating modes.

According to another aspect of the invention there is provided radar apparatus for detecting an object in through wall and related applications, the radar apparatus comprising: means for transmitting radar signals (e.g. a transmitter); means for receiving reflected portions of said transmitted signals from said object (e.g. a receiver); wherein said radar apparatus is configured for operation in any of at least a first and a second selectable mode; wherein said transmitting means is configured for transmitting radar signals in accordance with a selected one of said modes of operation, and said receiving means is configured for receiving said reflected portions of said signals transmitted in accordance with said selected mode of operation; and wherein said radar apparatus is configured for transmission of signals, through an obstacle, to said object when operating in at least one of said modes.

The radar apparatus may be configured for transmission of signals, through an obstacle, to said object, when operating in each of said modes.

The obstacle may comprise building material (e.g. wood, stone, plasterboard, concrete, bricks, blocks or the like), and may be in the form of, for example, building rubble or a fence, wall, and/or other manufactured partition.

Preferably, the operating modes are characterised by the form of the transmitted and received radar signals. Preferably, the transmitter and/or receiver means are adapted to transmit and/or receive high bandwidth signals when the radar is operating in at least one (e.g. the first) mode. More preferably, the transmitter and/or receiver means are adapted to transmit and/or receive ultra- wideband (UWB) signals when in at least one (e.g. the first) operating mode.

5 Preferably, the transmitter and/or receiver means are adapted to transmit and/or receive short impulse signals. More preferably, approximately between 1 and 20 million or more preferably 2 and 10 million pulses are transmitted per second. More preferably, approximately 5 million (say between 3 and 8 million) pulses are transmitted per second.

Preferably, the transmitter and/or receiver are adapted to operate at approximately between 10 200MHz and 4GHz when in at least one (e.g. the first) operating mode. More preferably, the transmitter and/or receiver are adapted to operate at approximately 2 or 3 GHz when in at least one (e.g. the first) operating mode.

Preferably, the radar comprises circuitry adapted to operate in either of the at least two operating modes. More preferably, the circuitry comprises at least one internal oscillator connectable to a 15 transmitting antenna.

Preferably, the radar further comprises means for comparing reflected signals received by the receiver means with the transmitted signals.

Preferably, the comparing means is adapted to detect positional information more accurately when the radar is in at least one (e.g. the first) operating mode.

20 Preferably, the receiving means comprises a plurality of receiving antennas.

Preferably, the receiving antennas are mounted in an array. More preferably, the receiving antennas are mounted are mounted in close proximity to one another. More preferably, the spacing between the arrays is approximately of the order of 10 (say 1 to 20) wavelengths of the centre frequency of operation. More preferably, the arrays are spaced such that the distance 25 between adjacent antennas is of the order of 3 wavelengths of the centre frequency of operation.

Preferably, the radar further comprises means for measuring the angle of incidence of received reflected signals. More preferably, the measuring means comprises means for measuring the elevation and azimuth angles.

Preferably, the transmitter and/or receiver means are adapted to transmit and/or receive lower 30 bandwidth signals when the radar is operating in at least one (e.g. the second) mode. More preferably, the transmitter and/or receiver means are adapted to transmit and/or receive narrowband signals when in at least one (e.g. the second) operating mode.

Preferably, the transmitter and/or receiver means are adapted to transmit and/or receive a relatively continuous narrowband signal (i.e. with higher than a 50 or 75% duty cycle, preferably a 35 100% duty cycle) when in at least one (e.g. the second) operating mode.

Preferably, the transmitter and/or receiver means are adapted to operate at approximately between 200MHz and 4GHz when in at least one (e.g. the second) operating mode. More - A -

preferably, the transmitter and/or receiver means are adapted to operate at approximately 2 or 3 GHz when in at least one (e.g. the second) operating mode.

Preferably, the circuitry comprises at least two oscillators. More preferably, the circuitry comprises a stable oscillator for use in generating narrowband signals. In an embodiment this stable oscillator may be an external oscillator. More preferably, the circuitry is adapted to switch between the two oscillators in dependence on the mode of operation of the radar.

Preferably, the comparing means is adapted to detect movement information more accurately when the radar is in at least one (e.g. the second) operating mode.

Preferably, the radar is further adapted to operate in at least a third operating mode. More preferably, at least one (e.g. the third) operating mode is an intermediate operating mode.

Preferably, the transmitter and/or receiver means are adapted to transmit and/or receive gated narrowband signals when the radar is in at least one (e.g. the third) operating mode.

Preferably, the transmitter and/or receiver means are adapted to transmit and/or receive coded narrowband signals when the radar is in at least one (e.g. the third) operating mode. Preferably, the radar further comprises circuitry adapted to modulate the narrowband signal. More preferably, the circuitry comprises means for modulating the narrowband signal with a code. More preferably, the code is in the form of a 32Mbits/sec 1024 bit code. In an embodiment the modulating means comprises a configurable complex programmable logic device (CPLD). Preferably, the comparing means is adapted to provide enhanced range discrimination information when the radar is in at least one (e.g. the third) operating mode.

According to another aspect of the invention, there is provided a method of detecting the presence of persons within a structure, behind a wall and/or beneath a collapsed structure using the radar as described herein. Preferably the method is adapted to provide information relating to the layout and content of a structure (for example a building) including the location of static and moving items within the structure. More preferably, the method is adapted to provide information regarding the presence and location of persons within a structure, behind a wall and/or beneath a collapsed structure. In particular, the method is adapted to be employed in security operations, for example anti-terrorist or hijack situations and in search and rescue operations.

Preferably, the method is adapted to provide enhanced object position detection when the radar is in at least one (e.g. the first) mode of operation. More preferably, the method is adapted to provide enhanced tracking capability when the radar is in at least one (e.g. the first) mode of operation (ultra-wideband mode). This is due to the range sensitivity provided when the radar operates in ultra-wideband mode.

Preferably, the method is adapted to provide enhanced detection of movement when the radar is in at least one (e.g. the second) mode of operation. This is due to the movement sensitivity provided when the radar operates in narrowband mode. In this way it is possible to detect "signs of life" within the structure.

Preferably, the method is adapted to provide range discrimination when the radar operates in at least one (e.g. the third) mode. In this way it is possible to isolate detected activity to a within a particular location.

Preferably, the radar further comprises means for varying range sweep when the radar operates in the gated and/or coded narrowband mode. More preferably, the range varying means may be manually selectable. More preferably, the range varying means may be programmable.

Preferably, the switching means is adapted to be operated manually. More preferably, the switching means comprises means for automatically switching between the operating modes in dependence on whether or not an object is detected in a particular mode of operation. In one embodiment, the radar may begin scanning a structure in at least one (e.g. the first) operating mode, and if nothing is picked up during this scan, the radar may automatically switch to either a narrowband mode or a gated narrowband mode. Preferably, the comparing means is adapted to compare both the reflected signal and a phase shifted version of the reflected signal. More preferably, the comparing means is adapted to compare the reflected signal and a 90 degree phase shifted version of the reflected signal thereby to provide enhanced detection sensitivity. More preferably, the comparing means is adapted to use an IQ (in-phase / quadrature phase) sampling method when processing the reflected signal. More preferably, the IQ sampling method is adapted to operate when the radar is in both the first (UWB) mode and/or the second (narrowband) mode and/or the third (gated narrowband) mode of operation.

Preferably, the radar comprises means for processing received signals. Preferably, the processing means may comprise means for post-processing received signals. Preferably, the processing means comprises means for analysing the content of reflected narrowband and/or gated or coded narrowband signals. More preferably, the processing means comprises analysing the frequency content of the reflected signals. More preferably, the processing means comprises means for performing a Fourier transform on the reflected signals, and in particular, a Fast Fourier Transform (FFT) on the reflected signals. Yet more preferably, the processing means comprises means for performing micro-Doppler analysis on the reflected signals. In this way it is possible to detect a heartbeat or respiratory activity within a structure. Furthermore, it is also possible to distinguish the number of persons within the structure due to differences between each person's heart and/or breathing rate.

Preferably, the processing means is adapted to perform further processing operations on received signals, for example, a wavelet or Bayesian analysis or lag subtraction may be performed on received signals.

Preferably, the radar is portable. More preferably, the radar and all its circuitry are mounted within a single housing which may be transported and operated by a single user. More preferably, the housing is ruggedised. Preferably, the radar is adapted to be positioned against an outer wall of a structure to be scanned.

Preferably, the radar is mountable to a tripod proximate to an outer wall of a structure to be scanned. More preferably, the radar is adapted to be positioned approximately between 1 and 20 meters away from an outer wall.

Preferably, the radar is adapted to be mounted to a vehicle, for example, a land based vehicle and/or an airborne vehicle.

Preferably, the radar further comprises means for displaying objects detected by the radar. More preferably, the display means is adapted to visually indicate the relative confidence of the detection of an object. More preferably, the colour of visual indicators on the display may indicate the detection confidence.

Preferably, the display is adapted to display the detected object in two and/or three dimensions. More preferably, the display means is adapted to display the object on a grid.

Preferably, the display means is adapted to display the results of any processing and/or post- processing operations performed on received signals. More preferably, the display means is adapted to display at least one of the following: the raw signal data; an FFT spectrogram; an "activity" plot; a wavelet analysis plot; a lag subtraction plot; or a "direction" plot.

Preferably, the radar comprises means for connecting the radar to an external processor, for example, a PC. More preferably, the radar comprises means for connecting the radar to a laptop.

Preferably, the processing means may at least in part be located externally.

The transmitter (and/or receiver) means may be adapted operate mono-statically when the radar is operating in at least one (e.g. the first) of said modes. The transmitter (and/or receiver) means may be adapted operate bi-statically when the radar is operating in at least one (e.g. the second) of said modes. The transmitter (and/or receiver) means may be adapted operate multi-statically, operating in a mono-static mode or a bi-static mode in dependence on propagation conditions.

According to another aspect of the invention, there is provided a radar system which comprises a radar as herein described and means for connecting the radar to an external processing device.

Some of the advantages of the radar and/or method or system as described herein include:- • Smaller size of radar unit: An integrated system has the ability to share common signal processing components and also common antennas which are likely to drive the overall size of the unit.

• Simplified mode switching: A common architecture enables the processing between the systems to be more easily integrated together in terms of software and hardware interfaces. • Improved performance: Integration of the receiver antennas into a common unit simplifies the setup of the system in operational scenarios. Orthogonal Array

Preferably, the radar further comprises means for connecting the radar to at least a further similar radar.

Preferably, the radar further comprises means for connecting the radar to a remote central processor.

According to another aspect of the invention, there is provided a radar system, which comprises at least two radars as herein described, a central processor adapted to processes the outputs of multiple radars and means for connecting the or each radar to the central processor.

According to another aspect of the invention, there is provided a radar system for detecting an object in through wall and related applications, the system comprising: at least two radars each configured for transmission of signals, through an obstacle, to said object; a central processor adapted to process the outputs of each radar; and means for connecting each radar to the central processor.

Preferably, the connecting means is adapted to connect the or each radar directly to each other. Preferably, the central processor comprises means for processing the outputs of the or each radar in the light of the relative positions of the radars with respect to an area being scanned.

Preferably, the processing means is adapted to process the outputs of the or each radar in the light of the approximately right angled positioning of the radars with respect to one anther. More preferably, the processing means is adapted to process the outputs of the or each radar in the light of the orthogonal positioning of the radars with respect to one another.

Preferably, the processing means is adapted to compare the processed outputs of the or each radar. More preferably, the processing means is adapted to process the reflected signals received by the or each radar.

Preferably, the system comprises at two radars, and more preferably at least four radars, adapted to be positioned around an area and/or structure to be scanned, with a first pair being positioned in an orthogonal orientation to a second pair.

Preferably, the system comprises a plurality of radar pairs, each radar in the pair being adapted to be positioned in an orthogonal orientation to each other.

According to another aspect of the invention, there is provided a method of scanning a structure using a plurality of radars as herein described, the method comprising positioning the radars around the structure in an orthogonal orientation to one another, and combining the outputs of the radars.

Preferably, the radars are adapted to operate in at least one of the following modes: a bi-static mode, a mono-static mode and a multi-static mode. Preferably the radars are operable in a mono-static mode or a bi-static mode in dependence on propagation conditions. More preferably a pair of said radars is operable bi-statically in dependence on attenuation in a mono-static path to at least one of said radar pair.

Preferably, the radars comprise means for determining position and/or velocity information using coherent integration of successive radar scans thereby to highlight targets moving at specific range rates.

Hence, there is provided preferably a plurality of modes of operation. This is particularly important when examining a building, for example for signs of life.

In a typical method of use, first, UWB/pulsed irradiation is employed, preferably to examine the nearest part of the building (say the nearest room or rooms).

Second, coded narrowband irradiation may be employed, which would give an indication of movement and possibly location in farther parts of the building (say farther rooms), achieved through an increase in mean power.

Finally, narrowband mode may be employed, in which an indication of activity in substantially the entire range is achieved through the use of micro-Doppler.

It will be understood that, in connection with the different modes of operation, UWB provides good positional accuracy, but achieves this with a short duty cycle and hence with lower mean power. In penetrating further into buildings, there is an advantage in having a higher mean power. Also, as the duty cycle is extended the bandwidth of the receiver becomes band limited and the noise floor drops. Greater mean power and the drop in the noise floor increases sensitivity. However, this is at the expense of positional accuracy.

The invention also provides a computer program and a computer program product for carrying out any of the methods described herein and/or for embodying any of the apparatus and or system features described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein and/or for embodying any of the apparatus and or system features described herein.

The invention also provides a signal embodying a computer program for carrying out any of the methods described herein and/or for embodying any of the apparatus and or system features described herein, a method of transmitting such a signal, and a computer product having an operating system which supports a computer program for carrying out any of the methods described herein and/or for embodying any of the apparatus and or system features described herein.

The invention extends to methods and/or apparatus and or systems substantially as herein described with reference to the accompanying drawings. Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, features implemented in hardware may generally be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly.

The invention is now described, purely by way of example, with reference to the following description and appended drawings.

Multi-Function System

Micro-Doppler (narrowband), time-gated narrowband or coded narrowband, and Ultra Wide Band (UWB) mode radar using a single architecture (with a minimum of component modifications or using software definition). In one embodiment the transmitted waveform is altered thereby to increase the duty cycle of the transmitted wave and to increase the power illuminating the target and received by the system. This in turn decreases the range resolution of the system but increases sensitivity.

The transmitted waveform may also be coded or different frequencies used to mitigate multi-path propagation effects in the system. Applications include Ultra Wide Band (UWB) location, determining room occupancy, breathing and heart rate detection, automotive applications (such as parking distance measurement and collision avoidance), defence applications, transport and marine applications, and operation against wall and at stand-off range typically of 1 metre to 20 metres.

The architecture may be used for through wall operation by modifying the operating frequency band of the hardware, and enabling external components to be interfaced to this board to support narrowband operation.

The system has the potential to operate in a gated narrowband mode to provide a limited amount of range resolution as a Doppler sensor. The hardware may support this mode of operation. The system may communicate to a PC via USB which will run the processing algorithms. Systems may be combined into a single unit with a common set of antennas and single processing PC.

The system may comprise a through-wall radar which is capable of operating at a standoff from a wall and can switch between broadband and narrowband modes and can provide accurate position measurement combined with highly sensitive signs of life detection through micro- Doppler analysis. For example its operating capabilities may include: coverage of 4m wide x 5m deep +/-1 m height; positional accuracy of 25cm RMS (Root Mean Squared) over the coverage zone; the ability to operate through a wide range of common wall materials; the ability to detect moving objects against a static background by clutter learning / rejection and intelligent tracking algorithms.

The system may comprise a radar unit and a PC (Personal Computer) unit, connected with a single umbilical cable.

The application software may run under the Windows (RTM) operating system. When applied as a compact radar unit for automotive applications at around 6GHz, this system may comprise a single printed circuit board containing 5 receiver channels with I/Q mixing and an on-board signal processor.

This system may be used as the basis for an integrated multimode through wall radar system optimised for stand-off operation.

Micro-Doppler User Interface

Sensitivity to vibratory variations may advantageously be improved by using signals at very high frequencies, significantly above those used for radar, at which the magnitude of the vibration becomes more significant in comparison to the wavelength of interest, or may even represent multiple wavelengths. For example, a LIDAR system using lasers operating at near to moderate infra-red frequencies may be used to improve vibration sensitivity. Such systems might typically use a wavelength of the order 1 to 10 μm corresponding to a frequency between 300 and 30 THz respectively. Such a system is inherently limited to line of sight applications, is sensitive to atmospheric conditions (e.g. can rendered inoperative by rain, clouds, and fog), and requires accurate alignment with an object of interest. Furthermore lasers are not suitable for wide-area surveillance because of their relatively small physical aperture area.

It would be advantageous, however, if the information could be derived regardless of whether the object of interest was obscured by an obstacle such as a wall or the like. It would also be beneficial if the system could be used in a range of atmospheric conditions. However, at the low frequencies required to allow penetration of obstacles, the sensitivity to micro-Doppler type effects becomes compromised and, with current processing technology, very scale variations/movements such as those of oscillatory or otherwise fluctuating components becomes impossible to extract.

Furthermore, the variation information is preferably derivable regardless of whether the object was moving at speed or substantially stationary.

It would be of further benefit if, in addition to the variation information, other information could be derived about the detected object, for example: information relating to macroscopic movements (velocity, acceleration, trajectory, or the like); two or three dimensional positional information (range, angular position, azimuth angle, height); and other information relating to the size or shape of the object.

Accordingly in one aspect of the invention there is provided apparatus for detecting variations in the motion (e.g. movements / relative movements) of at least part of an object, the apparatus comprising: means for transmitting a signal; means for receiving a reflected portion of said transmitted signal from said object; means for processing said received signal to detect said variations/movements; and means for generating an audio signal, said audio signal changing in dependence on said variations/movements.

According to another aspect of the invention there is provided radar apparatus for detecting movements (e.g. relative movements) of at least a part of an object, wherein said movements have magnitude less than a wavelength of signals transmitted by said radar, the apparatus comprising: means for transmitting said radar signals; means for receiving reflected portions of said transmitted signals from said object; means for processing said received signal to detect said movements; and means for generating an audio signal, said audio signal changing dependent on said movements. Preferably the radar apparatus is configured for transmission of signals, through an obstacle, to said object.

According to yet another aspect of the invention there is provided radar apparatus for detecting movements (e.g. relative movements) of at least a part of an object, wherein said radar apparatus is configured for transmission of signals, through an obstacle, to said object, the radar apparatus comprising: means for transmitting said radar signals; means for receiving reflected portions of said transmitted signals from said object; means for processing said received signal to detect said movements; and means for generating an audio signal, said audio signal changing dependent on said movements.

Preferably the radar apparatus is operable for detection of movements having magnitude less than a wavelength of the transmitted signal. More preferably the radar apparatus is operable for detection of movements having magnitude less than half a wavelength of signals transmitted by said radar or even more preferably movements having magnitude less than a quarter of a wavelength of signals transmitted by said radar.

Preferably transmitting means is configured to transmit said signal at a frequency below infrared. The transmitting means may be configured to transmit said signal at a radio frequency and preferably a frequency below 8GHz. The transmitting means may be configured to transmit said signal at a frequency between 1 and 4GHz or may be configured to transmit the signal at a frequency between 200MHz and 1GHz. Alternatively the transmitting means may be configured for transmission at higher frequencies, preferably between 8GHz and 25GHz, for example ~10GHz (e.g.) 10.125GHz or ~24GHz (e.g. 24.25GHz).

The variations/movements may, for example, be fluctuations in a component of the object. The variations/movements may represent movement of magnitude less than a wavelength of the transmitted signal and may represent movement of magnitude equivalent to only a fraction of the wavelength. For example, a 4GHz signal having a wavelength of approximately 75mm is significantly greater than both variations/movements representing movement indicative of breathing (such as chest movement) and sound (vibrations).

The processing means is preferably configured to extract micro-Doppler effects from said received signal to detect said variations/movements. The processing means may be configured to process the received signal coherently with respect to the transmitted signal. Accordingly the processing means may comprise an in-phase and a quadrature channel.

Preferably the apparatus comprises means for processing (e.g. a signal processing circuit or the like including, for example, in-phase and quadrature channels) said received signal coherently with respect to the transmitted signal and may comprise an in-phase and a quadrature channel for IQ processing said received signal. Preferably the apparatus is operable in a mode in which said transmitted signal comprises a continuous wave. Alternatively or additionally the apparatus may be operable in a mode in which said transmitted signal is coded, and preferably phase coded. The apparatus may be operable to transmit multiple carriers, for example at different frequencies. The processing means is preferably operable to process the received signal to determine positional information about said object from said detection apparatus. The processing means may be operable to process said received to determine a range of said object from said detection apparatus.

The apparatus preferably comprises means for determining positional information about said object from (analysis of) said received signal. The apparatus may comprise means for determining a range of said object from (analysis of) said received signal.

The apparatus preferably further comprises means to set a range swath, and said processing means is preferably operable to process said received signal for objects detected within said range swath. The apparatus preferably comprises means to set a range swath, and may be operable to process received signals for objects detected within said range swath only. The range swath setting means may allow automatic and/or manual setting of said range swath.

The range swath setting means may allow automatic and/or manual setting of said range swath.

In particular the system over a timescale (for example, some seconds or minutes) may automate a sweep through separately phase coded range swathes, preferably gradually increasing the information available to the user and/or collating and processing the data before presentation to the user.

The apparatus may be further configured to record signals corresponding to multiple range swaths, preferably substantially simultaneously. Preferably an average of the recorded signals is discarded or otherwise taken into account when processing the signals. This advantageously allows elimination of signals from sources such as antenna movement, which would affect all ranges simultaneously. A true target of interest would only significantly affect a single range swath.

The processing means may be operable to process said received signal to determine a 2D and/or a 3D position of said object from said detection apparatus.

The apparatus may comprise means for processing said received signal to determine a 2D and/or 3D position of said object from said detection apparatus.

The frequency of the audio signal preferably varies in dependence on the detected variation thereby characterising said variation. The detected variations/movements may have a frequency and at least a component of the audio signal may be at said frequency. The variations/movements may comprise vibrations caused by sound, and the output means may be configured to produce an audio signal characterising said sound. The audio signal preferably reproduces the sound at least in part. The radar apparatus may be operable to generate an audio signal having a frequency which varies in dependence on detected movement thereby characterising said movement. The radar apparatus may be operable to detect movements having a frequency (e.g. vibrations, breathing, heartbeat etc.) wherein at least a component of said audio signal is at said frequency. The radar apparatus may be operable to detect movements comprising vibrations caused by sound, and to produce an audio signal characterising said sound. The audio signal may be capable of output via a transducer to reproduce said sound.

The apparatus may comprise means for converting audio signals generated by the apparatus into sound and/or may comprise means for connecting an audio output device for converting audio signals generated by the apparatus into sound.

The detected variations/movements may have a frequency and at least a component of the audio signal may be at said frequency or a filtered shifted or modulated signal deriving from said frequency. Preferably, for user comfort, DC levels may be removed or thresholding applied to said signal so that no activity in the field of view corresponds to no audio signal. Preferably the apparatus further comprises means for converting said audio signal into sound. Preferably the apparatus further comprises means for connecting an audio output device for converting said audio signal into sound.

The variations/movements may comprise life-sign indicators, and said output means is preferably configured to produce audio signal characterising said life-sign indicators. The life-signs indicators may comprise heart beat indicators and/or movements indicative of breathing.

The apparatus preferably comprises means for processing said received signal to provide a characteristic signature of said variations/movements.

Preferably the apparatus may supply information to the user using phase differences between dual audio signals (i.e. stereo), in particular the likely direction of a detected object (e.g. an individual) may be presented to the user using phase modulation of different channels thereby taking advantage of the highly efficient innate capability of a human brain to interpret direction from stereo audio.

The stereo may be derived from signals processed from different receive channels associated with different receive antennas. Preferably the apparatus is operable to generate a plurality of audio signals configured for providing a stereo output. The audio signals may be configured for providing said stereo output in dependence on corresponding signals received in a plurality of receive channels.

Preferably the apparatus comprises means for generating an audio signal, wherein the generating means comprises part of output apparatus; said output apparatus preferably comprises: means for converting an output signal from said radar apparatus into an audio frequency signal characterising detected movements. The conversion means may comprise a mixer for mixing said radar output with audio output to produce said audio signal. The conversion means may comprise a transducer for converting said generated audio signal into sound. The conversion means may comprise means for connecting a transducer for converting said generated audio signal into sound.

Preferably the apparatus is configured for detecting life-signs through obstacles by processing said received signal to detect movements (e.g. breathing, heartbeat, sound induced vibrations etc.) indicative of said life-signs.

Preferably the apparatus is configured: for remotely detecting oscillations and/or vibrations caused by sound; for processing said received signal to extract audio frequency vibrations of at least a part of said object; and for generating an audio signal, said audio signal changing dependent on said oscillations and/or vibrations. The apparatus may be configured for operation at a location remote from an obstacle (e.g. a wall) obscuring the object. The apparatus may be configured for operation against an obstacle (e.g. a wall) obscuring the object.

According to a further aspect of the invention there is provided output apparatus for a radar, the output apparatus comprising: means for converting an output signal from said radar into an audio frequency signal wherein said audio frequency signal characterises variations in the motion (e.g. movements / relative movements) of at least part of a detected object.

Advantageously the output apparatus effectively represents a user interface which allows the user to process radar data and to extract information which an automated system might otherwise fail to extract correctly. Preferably said conversion means comprises a mixer for mixing said radar output with audio output to produce said audio signal.

Preferably said conversion means further comprises a transducer for converting said generated audio signal into sound.

Preferably said conversion means further comprises means for connecting a transducer for converting said generated audio signal into sound.

Preferably the apparatus is configured for operation at a location remote from an obstacle (e.g. a wall) obscuring the object. The apparatus may alternatively or additionally be configured for operation against an obstacle (e.g. a wall) obscuring the object.

According to a further aspect of the invention there is provided apparatus for detecting life-signs through obstacles; means for transmitting a signal; means for receiving a signal reflected from an object, said received signal comprising at least part of said transmitted signal; and means for processing said received signal to extract variations in motion (e.g. movements / relative movements) indicative of life-signs; wherein said transmitted signal is at a frequency below infrared. Preferably the signal is at a radio frequency, for example a frequency below 8GHz. The signal may be at a frequency between 1 and 4GHz or may be at a frequency between 200MHz and 1GHz. Advantageously, therefore, the apparatus may be used to detect life-signs in situations where it would otherwise be difficult or impossible because of obstacles such as building rubble in an earthquake, or the like obscuring the source of the life-signs.

Advantageously, therefore, the apparatus may be used to remotely monitor sound in situations where it would otherwise be difficult or impossible because of obstacles such as walls, or the like, between the apparatus and the source of the sound. In essence, therefore, the apparatus may preferably be used as a microphone for picking up sound through obstacles. The preferable provision of audio output means advantageously provides a way in which a user may listen to the detected sound, remotely, through the obstacle. According to a further aspect of the invention there is provided apparatus for detecting variations in the motion (e.g. movements / relative movements) of at least part of an object, the apparatus comprising: means for transmitting a signal; means for receiving a reflected portion of said transmitted signal from said object; means for processing said received signal to detect said variations/movements; and means for providing an output characterising said variations/movements directly to a user; wherein said output changes in dependence on the variations/movements.

According to a further aspect of the invention there is provided apparatus for detecting life-signs through obstacles; means for transmitting a signal; means for receiving a signal reflected from an object, said received signal comprising at least part of said transmitted signal; and. means for processing said received signal to detect movements (e.g. breathing, heartbeat, sound induced vibrations etc.) indicative of life-signs; wherein said apparatus is configured for transmission of said transmitted signals, through an obstacle obscuring a source of said life-signs.

According to a further aspect of the invention there is provided apparatus for remotely detecting oscillations and/or vibrations caused by sound, the apparatus comprising: means for transmitting a signal; means for receiving signals reflected from an object, said received signal comprising at least part of said transmitted signal; means for processing said received signal to extract audio frequency vibrations of at least a part of said object; and means for generating an audio signal, said audio signal changing dependent on said oscillations and/or vibrations.

According to a further aspect of the invention there is provided apparatus for detecting movements (e.g. relative movements) of at least part of an object, the apparatus comprising: means for transmitting a signal; means for receiving a reflected portion of said transmitted signal from said object; means for processing said received signal to detect said movements; and means for providing an output characterising said movements directly to a user; wherein said output changes in dependence on the movements; and wherein said apparatus is configured for transmission of said transmitted signals, through an obstacle, to said object.

According to a further aspect of the invention there is provided a method of detecting life-signs through obstacles using the radar apparatus as described herein, the method comprising: processing said received signal to detect movements (e.g. breathing, heartbeat, sound induced vibrations etc.) indicative of life-signs. According to a further aspect of the invention there is provided a method of remotely detecting oscillations and/or vibrations caused by sound using the radar apparatus as described herein the method comprising processing said received signal to extract audio frequency vibrations of at least a part of said object; and generating an audio signal, said audio signal changing dependent on said oscillations and/or vibrations.

A preferable embodiment of the invention also provides a computer program and a computer program product for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein.

A preferable embodiment of the invention also provides a signal embodying a computer program for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein, a method of transmitting such a signal, and a computer product having an operating system which supports a computer program for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein.

A preferable embodiment of the invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa.

Furthermore, features implemented in hardware may generally be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly.

According to the present invention, there are provided methods, systems and apparatus as set out in the corresponding independent claims. Other preferable features of the invention are recited in the dependent claims.

The system is preferably designed to detect activity in buildings which may include (Doppler) - gross movement, and breathing and heart-rate (micro-Doppler) in an environment with substantial clutter (movement of other objects) from time to time. Provision of an audio interface advantageously allows a user to effectively separate clutter signals (e.g. caused by operator, unit or background object (tree) motion that the user can sense) from movement of people or animals within a building. This approach has benefits over a purely algorithmic approach because it allows the operator to correlate/discriminate observed (or sensed motion) from the radar output which contains this, from the motion of objects that are unseen / or not sensed by the operator. Advantageously, this may improve discrimination of both Doppler (e.g. λ/2 to multiple wavelength) and micro-Doppler (sub-wavelength e.g. < λ/4) motion from interfering signals.

The approach is of particular benefit when the system is deployed in stand-off mode (i.e. away from the support / stability offered by placing the unit against the wall and also in a low clutter environment where algorithm approaches can detect characteristics as small as breathing or heart rate. Advantageously, the approach may also allows provision of an unambiguous indication of gross movement in low clutter environment as well.

The apparatus may produce an output which falls into the audio band, and which may be processed using a conventional algorithm to provide a detection or processing gain above the level that can be achieved by eye which is particularly useful in a low clutter environment. The output may also be provided (directly) to a user in audio form (for example after basic audio processing) which is particularly useful in a high clutter environment

Advantageously the system is preferably coherent and hence may be used to provide an indication of motion towards the sensor and motion away from the sensor. Thus, when presented to the operator this provides additional information concerning a scene/location being analysed.

The use of a CW signal may be used, advantageously in order to mitigate transmit fading (object of interest placed in a deep fade for the frequency of operation), multiple frequencies (CW) waveforms and by extension, multiple carriers may also be used. CW also provides an advantage by increasing the duty cycle and hence mean power illuminating the object of interest. It will be appreciated that the term radar includes any radar apparatus having at least one transmitter and at least one receiver.

It will be appreciated that micro-Doppler variations may be extracted by analysing phase variations in a received signal.

Further information relating to the invention may be found in the following prior applications: International Patent Application No. PCT/GB96/02448, which names Cambridge Consultants Ltd as patent applicant and whose disclosure is incorporated by reference, discloses apparatus for and method of determining positional information for an object, including a method for determining the position of an object by means of detecting the relative timing of probe signals returned by said object at a plurality of spaced apart locations. International Patent Application No. PCT/GB93/01056, which names Cambridge Consultants Ltd as patent applicant and whose disclosure is incorporated by reference, discloses a method of and apparatus for detecting the displacement of a target, including a method for detecting the displacement of a target by means of comparing return signals from said target and stored reference data comprising data representative of the environment. International Patent Application No. PCT/GB94/00738, which names Cambridge Consultants Ltd as patent applicant and whose disclosure is incorporated by reference, discloses apparatus and method for displacement determination, data transfer and assessment, including a method for assessing the approach of an object to a specified point.

International Patent Application No. PCT/GB01 /00500, which names Cambridge Consultants Ltd as patent applicant and whose disclosure is incorporated by reference, discloses methods and apparatus for obtaining positional information, including a method for configuring transmitting and receiving antenna elements so as to provide for so-called "range gates" used in determining range by means of transmitting a series of signal pulses and detecting their reflections. Embodiments of the invention will now be described, by way of example only with reference to the attached figures in which:

Figure 1 is a plan showing a site under the surveillance of a radar system according to a first embodiment of the invention;

Figure 2 is a flow chart illustrating typical operation of multimode radar apparatus;

Figure 3 is a simplified block diagram of ultra wide band 'UWB' mode radar apparatus;

Figure 4 is a simplified block diagram of narrowband radar apparatus;

Figure 5 is a simplified block diagram of an integrated UWB and narrowband (multimode) radar apparatus for a multimode radar system;

Figure 6 is a photographic image of a hardware implementation of a radar apparatus;

Figure 7 is a Doppler radar time-domain plot for a human subject holding their breath;

Figure 8 is a Doppler radar time-domain plot for a human subject exhibiting a breathing pattern with a heartbeat superimposed;

Figure 9 is a (short-time) Fourier spectrogram showing breathing and heartbeat characteristics in a first scenario;

Figure 10 is a (short-time) Fourier spectrogram showing breathing and heartbeat characteristics in a second scenario;

Figure 11 is an illustration of Fourier analysis for a further scenario;

Figure 12 is a simplified block circuit schematic of a first embodiment of multimode radar apparatus for a multimode radar system;

Figure 13 illustrates the improved sensitivity, to micro-Doppler variations, provided by coherent in-phase (I) and quadrature (Q) processing of the received signal;

Figure 14 illustrates different range resolutions, maximum ranges, and integration times associated with different modes of a multimode radar system;

Figure 15 is a simplified block circuit schematic of a second embodiment of multimode radar apparatus for a multimode radar system;

Figure 16 shows a radar system; Figure 17 is a plan showing the site of Figure 1 under the surveillance of a radar system according to a further embodiment of the invention;

Figure 18 is a photograph showing a PRISM system;

Figure 19 is a simplified block diagram of a mono-static sensor configuration;

Figure 20 is a simplified block diagram of a bi-static sensor configuration;

Figure 21 shows a screenshot from a PRISM system;

Figures 22(a) to 22(c) show images from a PRISM system;

Figure 23 is a simplified overview showing a site under the surveillance of a radar system according to a further embodiment of the invention;

Figure 24 is a simplified block diagram of apparatus according to an implementation of the embodiment illustrated in Figure 23;

Figure 25 is an illustration of an possible antenna array suitable for use with the described embodiments;

Figure 26 is a simplified block circuit schematic of range selection circuitry for use with the embodiment of Figure 23;

Figure 27 is a simplified block circuit schematic of a circuit for use with the embodiment of Figure 23; and

Figures 28 and 29 show graphs illustrating range sensitivities as a function of the Pseudorandom Binary Sequence (PRBS) code tap size. Multimode Radar Overview

In Figure 1 a plan of a surveillance site is shown generally at 100. In the example the site is a building having a plurality of rooms defined by internal and external walls. The building is being illuminated by through wall radar apparatus 102 for detecting individuals in the building, and for determining their location to the extent possible.

The radar apparatus is operable in any of a plurality of modes including an ultra wide band (UWB) and a narrowband (continuous wave 'CW) mode of operation. Ideally, full positional information would be provided in the UWB mode, whilst discrimination information (i.e. discriminating between multiple occupants at the same or similar ranges) would be provided using the narrowband mode, throughout a building. However, in practice there may be limits on the performance in the different modes. In reality the performance of the radar system will degrade depending on the propagation conditions through the site, for example by the various internal walls or other partitions in the building, and this propagation may limit performance. In this regard, as seen in Figure 1 , the site 100 may be thought of as comprising a plurality of zones 104, 106, 108, based on differing capabilities of different radar signals to propagate through the site and return meaningful information.

In the UWB mode the broadband radar offers high range resolution (and hence accurate distance derivation) which can be combined with good 2D angle resolution when an appropriate antenna array (for example a 2x2 antenna array) is used to determine an accurate 3D position fora detected object. However, the relatively low mean power associated with the UWB mode of operation in combination with the distorting effects of the internal walls of the site mean that this mode is most effective for spaces behind the first (external) wall being illuminated, and in areas where there is a significant aperture (for example a doorway) to another room. For example, in Figure 1 the region in which the UWB mode is most effective is shown as zone 104. In the space beyond a second wall (or partition), beyond zone 104 in areas beyond a single (external) wall, where there is a significant aperture (for example a doorway) to another room, and at closer range through multiple walls (zone 106), positional detection accuracy in the broadband mode is reduced. In zone 106, however, whilst the accuracy of positional information is reduced, a degree of information is still available. For example, targets may still be detectable in the UWB mode, but the signal strength will be too weak to determine exact position, although a range estimate may be possible (e.g. from the radar's detection function).

In the space(s) at longer range and/or through additional walls (zone 108) the narrowband mode offers higher mean power and therefore can be used to determine occupancy through higher sensitivity, and to accurately discriminate between multiple occupants. The radar apparatus is also provided with an intermediate 'gated' narrowband mode in which a long pulse is transmitted to allow a coarse range measurement (when compared with the shorter pulse UWB mode), which can help to isolate detected activity to within a particular room. Whilst, the gated narrowband mode has a lower mean power than the CW (Continuous Wave) narrowband mode, it offers adequate performance in most cases and thus can represent a good compromise between discrimination and positional accuracy.

As an alternative (or in addition) to the gated narrowband option a 'phase coded' narrowband mode of operation may be provided in which the transmitted narrowband signal is phase modulated to allow radar returns in the range of interest to be filtered from unwanted returns at other ranges. Hence, radar Doppler clutter from large far away targets (or the like) can be suppressed when measuring targets with a building. Typically the transmitted signal may be modulated with a spread-spectrum pseudo-random code (also known as pseudo-random noise) such as a Pseudorandom Binary Sequence (PRBS) or similar.

If the occupants of any of the rooms are still (asleep, injured, hiding etc.) then the system may use micro-Doppler analysis in the narrow band modes (CW, gated, and/or phase coded) to determine presence by detecting signs of life (breathing and heartbeat motion). There may be a hierarchy in these measurements. For example, referring to Figure 2, a preferred mode of operation involves initially using the UWB mode (which offers good positional accuracy arid tracking of occupants in rooms), and then to degrade positional accuracy whilst increasing discrimination of occupants by using the narrowband CW mode of operation. If 5 applicable the intermediate (gated or phase coded) narrowband mode could be used as an intermediate step to using the continuous wave mode. The change between modes would be dependent on the UWB sensor not detecting any activity within the area. Where range is particularly difficult to measure accurately (e.g. in narrowband CW mode) the presence of individuals in further rooms could be determined by inference.

10 It will be further appreciated that whilst in the preferred embodiment a single carrier frequency is used (to keep cost to a minimum) the apparatus may be configured as a multi-carrier system (for example by transmitting multiple frequencies modulated as an Orthogonal Frequency-Division Multiplexing (OFDM) waveform) where cost is not a primary consideration. Such systems mitigate the effects of multipath propagation for the narrowband modes of operation.

15 UWB Mode Implementation

In Figure 3 a configuration of a UWB mode radar system is shown generally at 300. The radar system comprises four distinct components: an antenna unit 302; a radar unit 304; an interface unit 306; and a control/processing unit 308.

The antenna unit 302 comprises one or more external transmitter and receiver antenna(s) 20 optimised for stand-off operation. The receiver antennas are typically arranged to form an antenna array (for example, a two by two antenna array) with appropriate antenna spacing, arranged for derivation of 2D.

The radar unit 304 comprises a radar board appropriately configured for producing UWB radar signals for transmission from and for initial processing of signals received by the antenna unit

25 302. The radar board is configured to operate at a suitable frequency (for example 2GHz) and is provided with connectors for interfacing with the antenna unit 302, and for an SPI (Serial Protocol interface) link to export data to the interface unit 306. The interface unit 306 comprises an interface board board/card configured as a SPI to USB adaptor to provide a USB data link to the control/processing unit 308. The control/processing unit 308 typically comprises an external

30 personal laptop/ desktop computer (or the like) configured for processing radar data and for providing a Graphical User Interface for use by an operator of the system.

Narrowband Mode Implementation

In Figure 4 a configuration of a narrowband mode radar system is shown generally at 400. The narrowband mode system is based around a similar architecture to that of the UWB mode 35 system. Like the UWB mode apparatus 300, the narrowband mode apparatus 300 comprises a radar unit 404; an interface unit 406; and a control/processing unit 408.

To support narrowband mode operation, however, the narrowband apparatus comprises two distinct antenna units: a dedicated transmit antenna unit 410 and a receive antenna unit 402. The transmit antenna of the associated antenna unit 410 is a high gain antenna, and is positioned a greater distance from the receiver antenna array of the receiver antenna unit 402.

The narrowband mode apparatus 400 also includes an external (local) oscillatory source 412 for driving the transmitter signal. External oscillators typically have a better controlled phase noise than standard (internal) oscillators, although it will be appreciated that an internal local oscillator may, nevertheless, be used.

The radar unit 404 comprises a radar board configured for narrowband operation. The narrowband mode radar board 404 is provided with connectors for interfacing with the receiver antenna unit 402, the external source 412, and for an SPI (Serial Protocol interface) link to export data to the interface unit 406. The interface unit 406, the control/processing unit 408, and the receiver architecture are configured in a similar manner to the corresponding architecture described with reference to the UWB mode system of Figure 3.

Integrated System Implementation

In Figure 5 a configuration of an integrated UWB mode and narrowband (CW, gated, and/or coded) mode radar system is shown generally at 500. The system includes features from both the UWB apparatus 300 and the narrowband apparatus 400, and like parts are given like reference numerals.

The integrated apparatus 500 comprises a UWB branch 300' configured in a similar manner to the UWB system 300, and a narrowband branch 400' configured in a similar manner to the narrowband system 400. The branches 300', 400' however, share a common antenna unit 502 having a receiver array (as described previously) for both branches 300', 400', and at least one transmitter antenna for the UWB branch 300'.

The narrowband branch 400' is provided with a dedicated high gain antenna 402 driven by an associated external oscillator 412 as generally described with reference to Figure 4. Signals from the branches are processed by a common control/processing unit 508 comprising a laptop/desktop personal computer or the like, configured for switching between the two (or more) modes of operation.

Switching of the common antenna unit 502 between the UWB branch and the narrowband branch is provided for by a switching unit 510 comprising an RF switch or the like. The switching unit is controlled by a control line from a modified UWB radar unit 304' in the UWB branch 300'.

Signal Processing

The signal processing for the radar system combines a high resolution UWB algorithm with narrow band processing to support both positional accuracy in the UWB mode and breathing and heart rate detection and discrimination the narrowband mode(s). UWB Mode Processing

Processing in the UWB mode of operation comprises enhanced analysis/processing techniques directed primarily to enhancing performance during stand-off operation (away rather than against a wall) and which may include, for example, signal subtraction and adaptive thresholding to reduce the effect of initial wall reflections.

System operation is adapted to take into account signal characteristics such as signal to noise ratio and phase consistency as these measures may degrade in complex scenarios. Angular information may be sacrificed and range only measurements provided.

Narrowband Mode Processing Whilst known Doppler processing techniques may be used to detect individuals moving about within a site being surveyed, a number of techniques are provided for the detection of people who are very still (e.g. asleep, sitting at a desk, injured or deliberately hiding). These techniques are adapted to detect humans through small characteristic movements associated with body functions, and in particular regular movements such as breathing and/or heartbeat. Such analysis is carried out in the micro-Doppler region, where such movements cause small phase disturbances in a received return signal of the order of a fraction of a wavelength. For example, data from a human subject exhibits a distinct micro-Doppler structure from which breathing and heart beat can be identified.

Short-time Fourier transforms are typically used to generate spectrograms showing signal intensity over a range of Doppler frequencies as a time progression. The profile of the frequency content can be used to indicate the presence of human subjects and in some circumstances analysis of the detail can be used to discriminate between two individuals (for example where heart and/or breathing rates are sufficiently different). Among the factors which affect the intensity and shape of the micro-Doppler characteristics are: the stress level of the subject; the angle from which they are viewed; their clothing; and even gender specific factors.

There are several parameters of the short-time Fourier transform which may be optimised to bring out desired features of the spectrogram, these parameters include, for example, time window length and the window function used.

The characteristics of the spectrogram may also be used to infer additional information about a subject, beyond the provision of (2D, 2.5D or 3D) positional information about the subject(s) to which it relates and/or discrimination between subjects. Such information may be used, for example, for classification purposes, enhanced discrimination (e.g. presence of a plurality of distinct heart beats), and/or the like.

Radar returns from a subject attempting to avoid detection by holding their breath, for example, exhibit a significantly clearer heartbeat signal, generally in combination with a measurably increasing stress level. This can be seen by comparing the radar time-domain plots of Figure 7 (showing a heartbeat of human subject who is holding their breath) and Figure 8 (showing a breathing pattern with a heartbeat superimposed). Figure 9 shows a short-time Fourier transform spectrogram for a first scenario. The spectrogram exhibits both breathing 900 and heartbeat 902 characteristics. The heartbeat 902 exhibits a higher intensity due to the greater associated movement. Furthermore, the heartbeat has richer harmonics 904 due to the relatively sharp shape of the pulse. Figure 10 shows a short-time Fourier transform spectrogram for a second scenario. The spectrogram exhibits breathing 1000 and heartbeat 1002, 1004 characteristics for two different people detected by the multi-mode radar apparatus. The spectrogram illustrates how the two people can be discriminated by their different heart rates, despite their breathing rates being similar. The short-time Fourier transform advantageously includes several parameters which may be varied to enhance features of interest from the spectrogram. These include both the time-window length and the window function selected. A longer time window, for example, may be used in the Fourier analysis to give greater frequency resolution, thereby enabling fine discrimination of different frequency components. Alternative techniques provide improvements in discrimination performance, for example: cyclo- stationary signal analysis, which provides an improvement for signals that are periodic, but which exhibit a slow variation with time (such variation being typical to both breathing and heartbeat); alternative time-frequency representations (wavelet analysis, Wigner-Ville distribution), which provide optimisation of resolution in the time and frequency domains; and/or Bayesian analysis, which use a-priori information concerning heart rate and breathing waveforms.

A target tracking algorithm may also be provided optimised for operation on a through wall system. Similarly a clutter processing algorithm may also be provided optimised for the through wall case.

Hardware Implementation In certain cases the multiple modes of operation could be implemented on a single board with a number of shared components used for different modes of operation and with software and/or firmware used to implement different transmit and receiver schemes. Alternatively, the multiple modes of operation could also be implemented using a common architecture but with a minimum of component changes for each solution such that the implementation comprises a plurality of individual radar boards, each (for example) implementing a different mode of operation for the system.

A typical hardware configuration of a radar board configured for implementation of a 6 GHz single-board imaging radar system is shown in Figure 6, by way of example only. As illustrated by Figure 6 an integrated system provides potential advantages of compact size (e.g. ~80mm x ~150mm in the example) and reduced weight over separately implemented modes of operation.

Appropriate mixer circuitry and oscillator designs are used for the chosen frequency of operation. It will be appreciated that the selection of operating frequency is application dependent and is generally a compromise between providing the transmitted signal with an ability to penetrate solid materials, whilst ensuring an antenna size which is small enough to allow the detection apparatus to be compact and portable. Typically, for example, frequencies below 8GHz (e.g. 5.8GHz) and preferably in the range 1GHz to 4GHz (wavelengths between ~300mm and ~75mm) are suitable (e.g. typically 2.4GHz) although significantly lower frequencies may be used, for example, 868MHz or 200MHz (wavelengths of ~0.35m and ~1.5m respectively). It will be appreciated, however, that in other embodiments frequencies above 8GHz may be used. Particularly advantageous examples of this include 10.125GHz and 24.25GHz.

At the lower frequencies (e.g. < 8GHz), for example, the signals are able to penetrate obstacles such as wall constructed from steel reinforced concrete, bricks / blocks / tiles, combinations of such materials, or the like. Nevertheless, the higher frequency signals ~10GHz or ~24GHz are still capable of penetrating plasterboard / wood walls. Generally, however, for many building materials operation around 2GHz is still preferred.

It will be appreciated that separate antennas may be fed through coaxial connections. Suitable component selection and interconnection allows optimised configuration of the board(s) for UWB and narrow band modes of operation. It will be appreciated that whilst the apparatus is shown (in Figure 1) and described in terms of operation at a location remote from the site being surveyed, the apparatus may alternatively or additionally be configured for placement against (or even within) the wall of the building to allow detection and analysis of signals reflected from an object obscured by it.

Generally operation against a wall requires a broad beam pattern (+70°) for wide coverage, whilst for standoff operation a more directive antenna may be used, allowing a gain advantage whilst still maintaining room coverage. Any suitable design of antenna may be used for directive, broadband antennas, including (but not limited to) variants of Vivaldi antennas, horns and tapered horns.

The UWB and narrowband mode systems may be combined in a common enclosure with a common processing unit.

First exemplary implementation

A first implementation of multimode radar apparatus is shown in the radar subsystem block diagram of Figure 12 generally at 1200. For clarity, in Figure 12 the following acronyms are employed: SPI (Serial Protocol Interface), ADC (Analogue to Digital Converter), SPDT (Single Pole Double Throw) and LNA (low Noise Amplifier).

The apparatus 1200 comprises: a plurality of receiver branches 1202 (only one of which is shown in detail); a first transmitter branch 1204 for transmitting a UWB signal; a second transmitter branch 1206 for transmitting a narrowband signal; and control/processing circuitry 1208.

Each receiver branch 1202 comprises an antenna, a filter, at least one low noise amplifier (LNA), a mixer, and an audio amplifier arranged as shown. The antennas of the receiver branches may be arranged in an antenna array or the like. Although four receiver channels 1202 are shown, there may be any suitable number of channels, for example five, each containing a mixer as seen in Figure 12. The first (UWB) transmitter branch 1204 comprises a transmit antenna, an associated filter and a transmitter oscillator. The transmitter branch may be arranged in any suitable manner but typically comprises a pulsed UWB transmitter (e.g. a gated FET) with a band defining filter and is configured to transmit a carrier which is coherent with the gating signal, thereby giving pulse- pulse coherence. Provision of a band defining filter allows the operating band to be selected by modifying the filter.

The second (narrowband) transmitter branch 1206 comprises a high gain antenna, a power amplifier, a switched phase delay, and an external stable signal source. Whilst an external source is described it will be appreciated that a suitable local oscillator (having stability suitable for micro-Doppler operation) may be used. The switched phase delay is configured to provide phase diversity thereby avoiding nulls caused by multipath cancellation. In the narrowband modes one may either combine in phase the signals from the receiver channels to give a high gain receive path or measure angle of arrival using phase comparison.

The circuit may be configured to provide a gated CW (narrowband) mode. For example, for the gated CW mode the gating pulse on the transmit oscillator and local oscillator may be extended without significant hardware modifications.

The control/processing circuitry 1208 includes a local oscillator which is gated to produce an appropriate (typically narrow) range gate. The circuitry is configured for both in-phase (I) and quadrature (Q) mixing which is achieved, for example, by double-pulsing the local oscillator, with an appropriate time delay.

The control/processing circuitry 1208 includes a configurable complex programmable logic device (CPLD) from which a number of additional (relative to dedicated UWB operation) control lines 1220 are provided for allowing for multimode operation. The circuitry 1208 also includes a switching unit 1230 (for example a controllable single pole double throw 'SPDT' switch) which is controlled by the CPLD for switching operation of the circuit components for operation in different modes (UWB / narrowband).

To perform the additional signal processing associated with micro-Doppler analysis an additional DSP device 1232 is optionally provided in the circuitry 1208.

The architecture is also configured to provide (coherent) in-phase (I) and quadrature (Q) sampling thereby providing a number of advantages.

As seen in Figure 13, IQ sampling maximises the sensitivity of the design for both Doppler and micro-Doppler modes of detection in the narrowband mode. In the case of micro-Doppler movement of less than λ/4 (e.g. as typically seen for breathing and heart rate) IQ sampling ensures maximum (or optimum) sensitivity to small movements at any part of the waveform. For Doppler movement of greater than λ/2, (e.g. as seen for larger scale movement within a room) IQ sampling enables the direction of movement to be determined. IQ sampling also has advantages in the UWB mode, for example it reduces the number of data points required for a given range sweep which, in UWB mode, enables the complete sweep range to be covered by 128 samples, irrespective of the range sweep, since each range measurement includes a phase measurement. As seen in Figure 14 the modes may have different range resolutions and maximum ranges, along with different integration times.

In UWB mode the system typically operates as a conventional UWB radar system providing position information. For example, the system may operate as a short pulse system with coverage divided into 5 metre swaths each with 128 IQ samples (i.e. at 39mm resolution). The start distance may be programmed depending upon the stand-off range. The maximum range is typically a factor of the overall power budget. Since positioning performance and sensitivity may degrade with the number of wall interactions encountered, the system may also be configured to drop back to range information should the angle of arrival information become corrupted. In Gated Narrowband mode the system may operate as a conventional Doppler radar with an ability to process IQ returns for sensitive movement detection. For example, the system may use identical signal paths to the UWB mode but have firmware changes to reconfigure the system and processing. Coverage may typically be divided into 2 metre range swaths having a single IQ detection. The start distance may advantageously be programmed. The maximum range is typically set by source stability considerations.

The system may also be able to employ angle of arrival calculations at reduced accuracy.

Narrowband (CW) mode requires a stable source (typically external) and longer integration times. The stable source is typically switched in when required (e.g. by the CPLD via the SPDT switch). Processing techniques are similar to those employed in the gated narrowband mode. As described previously a separate high gain antenna may be provided for the narrow band transmitter and multiple receive antennas may be used to provide spatial diversity or in combination to provide additional gain.

Further exemplary implementation

A second implementation of multimode radar apparatus is shown in the radar subsystem block diagram of Figure 15 generally at 1500. The second embodiment comprises a four (receiver) channel system having a single transmitter. As described with reference to the first embodiment 1200 the design can be extended to N receiver channels, where N might be 16, 32 or any suitable number of channels.

As with Figure 12, Figure 15 is simplified and does not, for example, show all the control lines which may be provided from the CPLD (Complex Programmable Logic Device). It will be appreciated that a FPGA (Field Programmable gate array) or micro-controller may be used as an alternative (or in addition) to the CPLD. In addition the digitised data is fed to a separate DSP or processing engine (e.g. for micro-Doppler analysis or the like).

The multiple modes can be implemented in one of two ways: a single board implementation that can be configured for different modes by switching of circuit elements or as a common board architecture that enables different modes to be implemented on separate boards with a minimum of circuit modifications. Advantages include being able to extract a combination of narrowband and broadband information from a scene to determine location and presence in a single, compact sensor unit in varied propagation conditions.

UWB Mode of Operation The radar apparatus 1500 is configured to operate in UWB mode using a short transmitted pulse to accurately locate targets.

The apparatus 1500 includes a LO (local oscillator) switch 1510 arranged for selecting between a local oscillator 1502 and an external oscillator 1504, and for connecting a pulse formation circuit 1512 and an IQ modulator circuit 1514 to the selected oscillator 1502, 1504. In UWB mode the LO switch 1510 is set to select the LO 1502.

The pulse formation circuit 1512 is configured to coherently start the selected oscillator and to define its pulse length. This is then filtered before being switched (by LO Output switch 1540) to the output. The precise timing of the gated pulse is controlled by a timebase circuit (which is not shown). In UWB mode transmitter pulse coding is inactive. Receiver coding is also inactive.

The apparatus may optionally be provided with a power amplifier 1542 for further amplification of the pulse before radiation (transmission) by the transmit antenna 1544. In operation, the transmitted pulse propagates through space and is reflected (at least in part) by objects before being received by a receiver antenna. The apparatus comprises a plurality of receiver antennas 1516 (four in the example) configured to receive the (reflected portion of) incoming signal, and this is configured such that the system sees (in this case) four separate input signals. The receiver path includes a delay 1520 which in the UWB mode is set to zero.

The incoming signals are filtered and amplified initially a fixed gain amplifier 1522, and then by a variable gain amplifier 1524 (e.g. a continuously variable gain or a switched gain RF amplifier). The resulting amplified signal is provided as an RF input to an associated mixer device 1526. The LO drive to each of the four mixers is provided from the oscillator input to the transmitter circuit.

The IQ modulator 1514 provides a 90 degree phase shift at the centre frequency of the oscillator, which enables in-phase (I) and quadrature (Q) local oscillator drive signals to be routed to the mixer at successive times such that the system provides coherent detection of the incoming waveform.

Each receiver channel of the apparatus 1500 also includes a further filter 1530 and amplifier 1532 arranged to provide an output to a multiplexer 1534 such that in operation, the output from each of the mixers 1526 is filtered and amplified before being multiplexed. The multiplexed signal is output to a variable gain amplifier 1536 and then digitised by an analogue to digital converter 1538 before being processed using appropriate algorithms optimised for UWB detection. Uncoded Narrowband Operation

The radar apparatus 1500 is also configured for transmission a CW waveform in narrowband mode and to use micro-Doppler detection to detect small movements. This provides an increase in the mean power radiating the target and is optimised for narrowband operation. The configuration and operation are described below.

The LO switch 1510 is set to connect external oscillator 1504 (which typically has a better controlled phase noise than a standard local oscillator) via a (inactive) receiver phase coding unit 1506 and the (inactive) IQ modulator 1514 to the mixers 1526. In operation in narrowband (CW) mode the LO Output switch 1510 connects the antenna, via a (inactive) transmitter phase coding unit 1508, directly to the external oscillator 1504 by-passing the pulse formation circuit 1512 and associated filter.

As with UWB mode in narrowband (CW) mode transmitter and receiver phase coding are both inactive (not being required for transmission of a continuous wave).

As discussed previously the signal may be amplified by an optional power amplifier before radiation by the transmit antenna. In operation, the transmitted signal then propagates through space and is reflected (at least in part) by objects before being received by a receiver antenna 1516.

In operation in narrowband mode (CW) the receiver antennas 1516 receive the incoming signal, which is switched such that the system sums the signals from two elevation antennas (as seen in Figure 15). This further improves signal to noise ratio. It will be appreciated that the system could be configured to process full IQ data from all four channels by the addition of a further 4 input channels.

Incoming signals are then filtered and amplified by a fixed gain as generally described previously. The receiver paths of each elevation antenna pair are configured to include an in phase (I) and a quadrature (Q) path. The signal in the quadrature path is delayed by an amount equivalent to a quarter wavelength (by delay 1520). The I and Q signals are then amplified before being input to the associated mixer 1526. The oscillator drive to the mixer is provided from the external oscillator input to the transmitter circuit. The drive is provided to the four receiver mixer circuits 1526. The outputs of the mixers are filtered and amplified before being multiplexed, as described previously. The multiplexed output being amplified by the variable gain amplifier 1536 and digitised by the analogue to digital converter 1538. The processor then uses algorithms optimised for narrowband detection to process the received signals.

The final amplifier filter components are typically optimised to further reduce the bandwidth of the input signal and to suppress out of band noise.

In an alternative embodiment (I) and (Q) LO signals may be applied to the mixers with parallel RF inputs. Coded Narrowband Operation

Operation is similar to the uncoded narrowband operation described above. However, the transmitted signal is phase coded by the transmitter phase coding unit 1508. Addition of a code enables the narrowband Doppler response to be limited to a defined range swath thereby rejecting unwanted returns outside the area, and improving clutter rejection.

The transmitted narrowband signal is modulated by a 1024 bit code at 32Mbits/sec which biphase codes the output signal. The choice of code length and bit rate is arbitrary. Typically, however, it represents a 5 metre range swath (half width).

The oscillator drive to the receiver mixers is also coded (by the receiver phase coding unit 1506) with a 32Mbits/sec code that represents the specified range swath. This can be incremented in delay by 16ns (which corresponds to a 2.5 metre resolution in swath mid-point). In this way the system rejects signal returns at incorrect code offsets.

Coding also improves performance by widening the transmitted spectrum (in this case to 32MHz), which has the ability to mitigate multi-path propagation through walls. In a typical system, the coded waveforms are produced by a CPLD, and can be modified to change the defined range swath.

Gated Narrowband Operation

In a further variant, the short pulse (e.g. when compared with the UWB mode) can be lengthened to provide a longer pulse system with a transmitted wave with a significantly larger number of cycles. This enables the target to be illuminated by a higher mean power, improving signal to noise ratio.

In gated narrowband mode the system is configured to operate as a conventional Doppler radar, but with an ability to process IQ returns for sensitive movement detection. The system may be configured to use the signal paths associated with the UWB mode but have firmware changes to reconfigure the system and processing.

The system is typically configured to transmit pulses representing 2 metre range swaths having a single IQ detection. The start distance may advantageously be pre-programmed and may be reconfigurable. The maximum range is typically set by source stability considerations. Hence, the system may be configured to use either the stable external oscillator or the local oscillator. Summary

An embodiment of the system may implement an integrated wideband and narrowband through wall radar in a single system. In the narrowband system, algorithms may be used both to detect breathing and heart rate and to provide a measure of room occupancy.

The architecture for (enhanced) through wall operation may be provided by modifying the operating frequency band of the hardware, and by enabling external components to be interfaced to the board to support narrowband operation. The system may also be provided with the potential to operate in an 'intermediate' gated (and/or an 'intermediate' phase coded) narrowband mode to provide a limited amount of range resolution as a Doppler sensor

Thus, at least three modes of operation may be implemented: UWB Mode to determine position of occupants; gated (or phase coded) Narrowband Mode allowing determination of activity at a given range; and narrowband (CW) mode to detect small movements over a wider range and to provide discrimination of individuals through micro-Doppler processing (e.g. based on heart rate and / or breathing rate). Switching between the modes will be based on activity in the area of interest, illustrated in the flow chart of Figure 2.

Preferably the system will switch modes automatically, based on what has been detected, but an operator may alternatively/or additionally have the ability to select modes based on an interpretation of a specific scenario. The different modes have different range resolutions and maximum ranges, along with different integration times as illustrated in Figure 14.

Separate sensors may be used for the UWB mode and the narrowband mode of operation. These may be based on an adaptation of known hardware (for example a known automotive sensor board), but with different configurations and connectivity to external components. This may also include the use of antennas specifically configured for (enhanced) stand-off operation. In each mode, the system may communicate with a PC (or the like) on which the processing algorithms are implemented, via a USB connection or the like. The antennas may be configured to determine the level of performance that can be achieved by the system operating in the wideband and narrowband mode.

The UWB and narrowband modes or may be combined into a single unit, with a common set of antennas, and sharing a single processing PC. Such a system will typically comprise a straightforward means of switching modes within the system (based around a SPDT or the like) controlled by a PLD (e.g. a CPLD). Thus, the through-wall radar described herein may be capable of operating at a standoff from a wall and can switch between broadband and narrowband modes. The proposed system also allows provision of accurate position measurement combined with highly sensitive small scale movement (e.g. < λ/4) detection through micro-Doppler analysis (for example for signs of life detection). The radar apparatus may combine a UWB mode sensor and narrowband mode sensor based on a radar architecture developed for automotive applications at 6GHz. Such an architecture may be adapted to enable it to work at more appropriate frequencies for a through wall system and to enable it to be configured to the different modes of operation. The adaptations typically include: reduction of the operating frequency to around 2GHz; implementation of separate antennas optimised for stand-off operation at around 2GHz; and modification of the UWB system to operate at increased range and in stand-off mode of operation. This may include modifications to the radar timebase and software to reduce the effect of the first wall reflection; adaptation of hardware to operate in narrowband mode with additional external components; and enhanced software capabilities to provide discrimination of heart rate and breathing. The apparatus may be based on a system such as a Portable Radar Interior Space Monitor (PRISM) through wall radar system. PRISM is a system whose operation may be described in brief as:

Coverage: 4m wide x 5m deep x +/-1 m height; positional accuracy: 25cm RMS over the coverage zone;

Wall materials: a wide range of common materials;

Operation: detects moving objects against a static background by clutter learning / rejection and intelligent tracking algorithms.

The PRISM system consists of a radar unit and a PC unit, connected with a single umbilical cable as seen in Figure 16. The application software may run under any suitable operating system (for example, a known system such as a Windows (RTM) operating system or the like).

Advantages of an Integrated System

The modes of operation described previously can be provided by separate radar systems. However, there is considerable benefit in providing an integrated system which provides this functionality. An integrated system would have the following advantages:

Smaller size of radar unit: An integrated systems has the ability to share common signal processing components and also common antennas which are likely to drive the overall size of the unit.

Simplified mode switching: A common architecture will enable the processing between the systems to be more easily integrated together in terms of software and hardware interfaces.

Improved performance: Integration of the receiver antennas into a common unit will simplify the setup of the system in operational scenarios.

Combination of Data from Orthogonal Sensors Overview In Figure 17 the surveillance site 100 of Figure 1 is shown under the surveillance of a through wall radar apparatus 1700 according to a further embodiment of the invention.

In summary, the apparatus 1700 is configured to allow a plurality of orthogonal views into a building (typically two) to be used, and to combine range and range rate returns from the orthogonal angles to determine moving and static object positions. The apparatus 1700 can be extended to include bi-static radar techniques.

The ability of a Through Wall Radar to determine both range and range rate (e.g. from an Inverse Synthetic Aperture Radar or using other approaches) means that orthogonal views into a building offer improved discrimination of both static and moving objects. The moving targets tend to provide a maximal response when moving along a radar boresight and hence orthogonal sensors will provide optimum information for any arbitrary target path within a building. One preferred solution is to use the combination of mono-static and bi-static radar configurations as shown in Figure 17. The system 1700 comprises four radar sensors A, B, C, D all arranged to 'look into' the building 100 from different aspects, sensors B (1704) and D (1708) being arranged orthogonal to sensors A (1702) and C (1706). In Figure 17 a central processor (PC) (1710) is shown linked to each of the sensors to provide control and processing as required. It will be appreciated, however, that this may be provided by a wireless or wired connection and may use an appropriate communications protocol (e.g. TCP/IP).

Figure 17 also shows direct out of building paths between adjacent sensors. In the bi-static mode of operation, these paths form the baseline measurement for transmitter-receiver delay in the system, against which bi-static measurement paths may be calibrated.

Each of the sensors A (1702) to D (1708) is based around a Portable Radar Interior Space Monitor (PRISM) Through Wall Radar System (as mentioned previously). Each sensor is operable independently as a through wall radar recording responses from moving and/or static objects. This provides an indication of movement in the building and also allows static objects to be "painted in" due to person movement (in relation to the static object). A photograph of a PRISM system is shown in Figure 18 the radar unit for which is shown at 1800.

The data collected by the sensors can be combined, by the central processor, to form four orthogonal views of scattering centres within a wide Field of View. In the instance that the locations of the four sensors is known the views may be combined (for example, to advantageously provide an accurate three dimensional representation). This process thus offers distinct advantages over strictly independent sensor operation.

As seen in the example of Figure 17, a subject (e.g. a person) 1710 is located in a room within the site 100. However, the path from sensor D (1708) is subject to high attenuation (as is the mono-static return path to D (1708) shown as a dashed line 1708a). Hence, in this case the bi- static path 1708b to sensor A (1702) (in this case with view through the window) is preferential from a measurement point of view. Thus sensor A (1702) can obtain additional information over a purely mono-static approach. Furthermore, in the example, the subject 1710 is completely obscured from sensor C (1706) which therefore has not detected the person in the building.

The sensors (e.g. PRISM units) employ a number of algorithms to process the return signals with varying degrees of processing gain.

Bi-static operation has a number of advantages over mono-static reception and processing of signals, which include: preferential propagation; improved processing of Doppler information; and propagation estimation.

Preferential propagation relates to specific cases in which the bi-static measurement path has a preferential propagation path to the mono-static case (i.e. as described above).

The improvements in processing of Doppler information arise because Doppler processing is only effective when the target of interest is moving with a positive or negative range rate. In the case shown in Figure 17, the subject of interest is moving with maximum range rate with respect to (in this case away from) sensor A, and a minimum range rate (in this case substantially zero) with respect to sensor B. Hence, orthogonal placement of sensors, and the combination of their outputs significantly improves the overall ability of the system to obtain processing gain for Doppler returns.

In the case of propagation estimation, the mono-static and bi-static paths enable potential measurements to be taken concerning the overall attenuation of the building for example in the measurement path from sensor A (1702) to C (1704) and B (1706) to D (1708). In a sense, therefore, the data may potentially be used to derive an attenuation map or the like.

Mono-static Implementation

A block diagram of an implementation of a possible mono-static sensor configuration is shown generally at 1900 in Figure 19.

The system comprises a processing unit 1910, a radar sensor unit 1912, and an external antenna unit 1914.

The processing unit may comprise any suitable computer or the like, for example, a ruggedised laptop computer. The external antenna unit 1914 may be any suitable size but is typically approximately 90cm x 90cm (if required to provide sufficient gain for stand-off performance). The antenna unit may comprise a receiver antenna array (e.g. a two by two array for a four (receiver) channel system) and at least one transmitter antenna depending on requirements.

The radar sensor unit 1912 will be of a similar size to the PRISM unit 1800 in Figure 18, and is configured to communicate with the computer unit 1910 using an appropriate communication link (e.g. USB). Advantageously, the computer unit 1910 may also provide the ability to provide data over an Ethernet link.

Bi-static Implementation

A block diagram of an implementation of a possible bi-static sensor configuration is shown generally at 2000 in Figure 20. The bi-static configuration 2000 is similar to the mono-static configuration 1900 but includes a central controller unit 2002 in addition to a processing unit 2010 as described previously. The configuration 2000 also comprises an two radar units 2012, 2012' and two antenna units 2014, 2014' similar to the mono-static antenna unit 1912 of Figure 19.

Appropriately configured software is provided in the central controller and processing units 2002, 2010 for handling interaction between the two units 2002, 2010, for controlling the two radar sensor units 2012, 2012', and in particular for acquiring data both in a mono-static mode and a bi-static mode.

The configuration may also be provided with a timing synchronisation signal 2016 between the two radars to allow investigation of the bi-static mode of operation and characterisation of performance improvements without implementing any major hardware changes. In this way, test data may be collected in a known environment, for example, to validate the power budgets. It will be appreciated that wireless sensors may alternatively or additionally be deployed. Summary

A plurality of orthogonal views into a building (typically two) may be used, and the resulting data (e.g. range and range rate returns from the orthogonal angles) combined to provide additional information about moving and/or static object positions.

An embodiment of an appropriate orthogonal arrangement may comprise an interconnected set of sensors or radars that offer performance improvements due to the use of multi-static sensing techniques.

An embodiment may, for example, use a combination of mono-static and bi-static radar configurations (as shown in Figure 17) which shows Mono and Bi-Static Radar Operation. Such a system uses four radar sensors all looking into the building from different aspects and with sensors B and D orthogonal to sensors A and C. A central processor (e.g. a PC) is linked to each of the sensors. In practice, this is likely to be based around an appropriate communication protocol (e.g. TCP/IP) using wired or wireless connections. One application of the present invention may be to provide future capability for Military Operations in Urban Terrain (MOUT).

General description of PRISM system operation

To assist the understanding of the reader a suitable PRISM system will now be described in more detail. The PRISM system is an ultra-wideband radar, operating in either the band 1.1 - 1.6GHz or 1 - 2GHz. These operating bands have been selected for compatibility with emissions standards in Europe and the USA. The band of operation can be opened up to produce a narrower pulse and increase range resolution if permitted. An example PRISM system can be seen in Figure 18.

In general, lower frequencies are better at penetrating wall materials and higher frequencies lead to better range resolution, therefore the choice of frequency for the through-wall system is a balance between these requirements.

The system produces a narrow transmit pulse (typically 1 ns wide) and uses a sampling receiver to produce a single narrow range gate. The range gate is swept in range from zero to 5m in 1024 steps, at a rate of 20Hz. Allowing for 2-way propagation, this gives us 15 range samples per wavelength assuming 2GHz centre frequency.

The system has 4 receiver channels, connected to a 2 x 2 antenna array and determines the angle to each target detected in range by a phase comparison in azimuth and elevation. A coordinate transformation then places the target on a 3D grid. Figure 16 shows a system block diagram of a PRISM system, whilst Tables 1 to 6 detail of an example of a suitable PRISM system specification. Table 1 : system specification.

Table 2: environment: radar unit and umbilical:

Table 3: PC unit.

The display unit may be based on a ruggedised portable computer, containing appropriate control and visualisation software.

Table 5: computer.

As seen in Figure 21 the system is configured to display a plurality of different representations relating to the site being surveyed including a plan and a side view, plus an azimuth angle indicator and a progress plot of the closest object. The operator is also provided with the capability of (simultaneously) viewing the scene using a 3D perspective view and related 2D views (Figures 22(a) to 22(c)).

As seen in Figures 22(a) to 22(c) distinct objects may be colour coded to aid identification as they move around.

Numerical information is available on each object: the operator can place a cursor on the object to obtain information on x, y, z co-ordinates, x, y, z speed and signal strength.

The action may be frozen and re-started at the touch of a button. Advantages of a PRISM Approach

The PRISM system (Figure 18) has a number of notable advantages over more conventional radar systems for this application that will be described in the following paragraphs. 3D scattering centre location from a single, compact sensor: A PRISM system has the ability to extract the 3D co-ordinates of object scattering centres from a single, compact sensor. This is provides a considerable advantage in that the accuracy of conventional triangulation / trilateration approaches will be highly dependent on the variation of RCS and scattering centre location with angle and propagation conditions. Hence location needs to be completed with a short baseline such that the propagation conditions are not significantly different for the measurement paths.

Calibrated signal strength information: Knowledge of the 3D scattering position of an object and also the beam-pattern of the radar sensor allows the signal strength of the individual returns to be calibrated. In a through wall application, the signal strength will be a function of the actual Radar Cross Section (RCS) and wall attenuation, however, some information may be derived once the propagation has been estimated.

High Accuracy Doppler Information: A PRISM system generally employs a sensitive Doppler measurement technique to detect and report moving targets with a higher degree of accuracy.

Micro-Doppler User Interface Overview In Figure 23 a simplified overview of a variation detection system is shown generally at 2300. The system 2300 comprises detection apparatus 2310 having a transmitter unit 2312, an antenna array 2314, a receiver unit 2316, and an output unit 2318.

The transmitter unit 2312 is configured for producing and transmitting radar signals 2320, via the antenna array 2314, towards an object 2322 of interest. The receiver unit 2316 is configured for receiving and processing a return portion 2324 of the transmitted signal, via the antenna array 2314, when it is reflected from the object 2322.

The detection apparatus 2310 is configured for operation in one of two modes: a continuous wave (CW) (unmodulated) mode, and a phase coded (PC) mode in which the transmitted wave 5 is phase modulated with a spread-spectrum pseudo-random code (also known as pseudorandom noise) such as a Pseudorandom Binary Sequence (PRBS).

In the example shown in Figure 23 the object 2322 is essentially stationary, but includes both stationary components 2326 and fluctuating components 2328, as indicated by the oscillatory arrows A. It will be appreciated that the object could alternatively be moving on a macroscopic 10 level as well with the fluctuating components 2328 representing small variations relative to the overall motion of the object.

The object 2322 is obscured behind an obstacle 2330, such as a wall or the like. The obstacle 2330 is opaque to higher frequency electromagnetic radiation such as visible light, infra-red, etc, but is at least partially transparent to radiation at lower radar frequencies. Typically, for example, 15 the obstacle is at least partially transparent to very low frequencies of around 200MHz, preferably to frequencies in the range 1 GHz to 4GHz, and still more preferably to frequencies below 8GHz. For example, the object 2322 may represent a human being in a building, the obstacle comprising a concrete (possibly reinforced) or brick wall.

The apparatus is configured for converting extracted micro-Doppler information directly into an

20 audible output which varies in dependence on the nature of the variation detected thereby characterising the variation in audible form. This is a particularly beneficial feature of the apparatus because it provides an effective increase in the sensitivity of the system. The provision of the audio output means that micro-Doppler effects which cannot be distinguished from noise and/or other effects are not simply filtered out or ignored, as might occur for a crude visual output

25 in which but the audible variations are discarded, but are instead outputted, with the noise, directly to an operator.

Exemplary implementation

In Figure 24 a simplified functional block schematic of the detection apparatus 2310 is shown.

The transmitter unit 2312 of the detection apparatus 2310 comprises a CW signal generator 30 2410, a power splitter 2412, and a CW or phase coded branch 2418. The phase coded branch comprises a code generator 2416, and a modulator 2414.

The CW signal generator 2410 is configured for generation of a narrowband signal having a desired frequency and amplitude. The selection of frequency is a compromise between providing the transmitted signal with an ability to penetrate solid materials, whilst ensuring an antenna size 35 which is small enough to allow the detection apparatus to be compact and portable. Typically, for example, frequencies below 8GHz (e.g. 5.8GHz) and preferably in the range 1GHz to 4GHz (wavelengths between ~300mm and ~75mm) are suitable (e.g. typically 2.4GHz) although significantly lower frequencies may be used, for example, 868MHz or 200MHz (wavelengths of ~0.35m and ~1.5m respectively). It will be appreciated, however, that in other embodiments frequencies above 8GHz may be used. Particularly advantageous examples of this include 10.125GHz and 24.25GHz.

At the lower frequencies (e.g. < 8GHz) the signals are able to penetrate obstacles such as wall constructed from steel reinforced concrete, bricks / blocks / tiles, combinations of such materials, or the like. Nevertheless, the higher frequency signals ~10GHz or ~24GHz are still capable of penetrating plasterboard / wood walls.

It will be further appreciated that whilst in the preferred embodiment a single carrier frequency is used (to keep cost to a minimum) the apparatus may be configured as a multi-carrier system (for example using Orthogonal Frequency-Division Multiplexing (OFDM)) where cost is not a primary consideration.

Directionality of the apparatus may be tailored by adjusting the antenna beam patterns of a particular implementation. Thus the apparatus may be configured to give a broad indication of left / right and/or an indication of activity in a particular range swath. For example, the apparatus may be configured for narrowing the position of a detected object to a particular room (e.g. 3m x 3m) rather than a more precise location. This is particularly advantageous in applications where locating areas of activity is of primary interest rather than the precise position of a detected object.

In operation in the CW (unmodulated) mode the CW signal generated by the signal generator 2410 is transmitted via the CW branch 2410, and a transmission antenna 2470 of the antenna array 2314, toward the object 2322.

Use of continuous wave is particularly advantageous because it reduces the complexity of the circuitry in both the transmission and reception paths thereby reducing associated non-linearities and circuit noise. CW also allows targets to be accurately resolved in velocity without ambiguity and without the complex circuitry associated with pulsed systems. The enhanced sensitivity to Doppler variations enables micro-Doppler effects to be extracted at the receiver side without them being swamped by other effects, for example, (static) clutter or the like.

However, a CW signal, by itself, cannot be used to determine the range of a target without ambiguity. Whilst phase differences caused by target range can be extracted to give a range indication this only allows resolution of range within a wavelength of the received signal. Hence, range measurements using the CW mode are inherently ambiguous. Furthermore, the return signals reflected from objects at different locations, but moving at similar velocities (or stationary) can interfere with one another making variations associated with moving parts of each object difficult to resolve from one another.

In operation in the phase coded mode the CW signal generated by the signal generator 2410 is phase modulated before transmission. The code generator 2416 is configured to provide a pseudo-random spread spectrum code (transmit code 2415) which is used by the modulator 2414 to phase code the CW signal. The pseudo-random code has a long cycle, equivalent to several wavelengths of the CW signal. The length of the code determines the integration time or the signal update frequency and the level of suppression of unwanted targets at other ranges. Synchronisation of a reflected signal with a replica of the coded signal may then be used, in the receiver unit, to accurately determine the effective phase difference between the received signal and the transmitted signal, thereby allowing time of flight and thus range to be calculated. Range selection may be done by correlating the received signal with a delayed version (receive code 5 2417) of the transmit spreading code 2415. Hence, objects may be accurately resolved in range.

The use of phase coding allows a range swath of interest to be pre-selected by processing the reflected portion of the transmitted signal received at the receiver between predetermined delays thereby delineating the swath of interest. The range swath may be pre-selected manually by an operator of the system (for example using adjustment means 2484) or alternatively may be 0 selected automatically by scanning through different ranges to home in on a range including an object of interest. It will be appreciated that the range swath may be fixed (for supporting typical operations) or may be swept between limits determined whilst carrying out operations.

Manual or automatic pre-selection of a specific range of interest allows the signal returned from objects within that range swath to be coherently integrated over time. Thus, micro-Doppler effects 5 representing variations within the return signal will tend to be reinforced over time whilst spurious, inconsistent effects will tend to be attenuated. This is particularly beneficial in cases where the detected variations vary at a low characteristic frequency. For example, if the apparatus detects a stationary human object, and the variations of interest comprise chest movements associated with breathing, the variations have a magnitude in the order of mm and are likely to occur at a0 frequency of the order of 20 per minute. Similarly, heart beats are likely to occur in the range of 1 Hz to 2Hz.

The receiver unit 2316 comprises a local oscillator branch, an I/Q generation unit 2446, a code modulation unit 2447, mixer units 2444 and 2448, IF amplifiers 2442 and 2450, an in-phase channel 2456, a quadrature channel 2458, and a processing unit 2460. 5 The local oscillator 2410 generates a LO signal for down conversion of the incoming reflected radar signal to an intermediate frequency IF or zero IF, baseband.

In the continuous wave mode the coherent output from the LO is phase shifted in the quadrature hybrid unit 2446 to produce I and Q signals for the receiver mixers. The output of the mixer units 2444 and 2448 are then amplified before being further processed coherently in the in-phase and0 quadrature channels 2456, 2458.

In the phase coded mode of operation a time delayed replica of the pseudo-random code used to phase code the transmitted signal is produced by the code generator 2416. The replica modulates the CW LO signal from 2410 to produce a phase coded LO for mixing down the received signal. The replica may be phase shifted in dependence on the pre-selected range5 swath, if appropriate. Figure 26 shows a simplified block circuit schematic of a suitable range selection circuitry 2600 for use in the code generator 2416, comprising a clock 2610 and 10-bit pseudo random binary sequencer 2620 and selectable Vz clock delay circuit 2630.

The range sensitivity is determined by the Pseudorandom Binary Sequence (PRBS) code tap size. Figure 28, shows the basic range selection would be in 5m steps with a 32MHz clock. Use of the selectable Vz clock delay circuit 2630 enables the range sensitivity to be effectively doubled, with the range able to be moved in steps of 2.5m, as shown in Figure 29.

The encoded output is then phase shifted in the quadrature hybrid unit 2446 to produce I and Q signals for the receiver mixers 2444, 2448 for mixing with the received signal to produce decoded outputs at the IF.

The decoded signal is amplified in the IF amplifier and further processed coherently in the in- phase and quadrature channels 2456, 2458 to allow extraction of micro-Doppler and similar type effects indicative of small scale variations.

It will be appreciated that larger Doppler scale variations may also be extracted in the I and Q channels.

Thus the receiver unit 2316 is configured for fully coherent processing of the received signal in both in-phase (I) and quadrature (Q) channels. Coherent processing in both the I and the Q channels increases the sensitivity of the system to micro-Doppler type effects thereby making it possible for the associated small scale variations in motion to be to sensed and extracted using radar frequencies significantly below those which might normally be expected. For example, if a stationary object having fluctuating components happens to be located at a peak or trough of a waveform, the variations cause micro-Doppler effects which are difficult to extract from an in- phase component alone because the associated rate of change of movement is at a minima and therefore would only result in a very small signal output. The outputs of the two channels 2456, 2458 in both the continuous wave and phase coded modes is processed appropriately by the processing unit 2460 to improve signal to noise ratio to the extent possible and to extract the micro-Doppler effects. The processing unit is configured for coherent integration of the effects over time, for example, over multiple cycles of the pseudorandom coded transmitted signal to further reinforce effects of interest with respect to spurious, inconsistent, noise induced artefacts.

Integration may be achieved using any suitable means. For example, integration may be achieved using active filters the contents of which vary over time in dependence on the nature of the reflected signal received in subsequent time periods. A filter for extracting a particular characteristic may, for example, be split into a plurality of branches, each branch being representative of a possible value of that characteristic of the object dependent on its behaviour. For each subsequent time period over which integration occurs the contents of the branch closest to a value extracted from the received signal is reinforced, whilst the contents of the other branches are attenuated. Thus, over several cycles the branch most accurately representing the behaviour of the object is consistently reinforced even if the extracted value for a particular cycle is incorrect because of the effects of spurious noise or the like.

Each branch may, for example, represent different oscillatory behaviour of the variation being detected and therefore different micro-Doppler effects. It will be appreciated, however, that any other suitable technique for integration/micro-Doppler extraction could be used. The antenna array 2314 comprises at least one transmitter antenna 2470 for transmitting the CW/phase coded signal and a plurality of receiving antennas 2472. The receiving antennas each have dimensions typically of the order of half the wavelength of the transmitted signal and are spaced apart along or transverse to the direction of travel and across the principle look direction, in known relative positions.

The receiver unit 2316 comprises a channel 2316a, 2316b, for each receiver antenna 2472, each channel being configured for coherent processing of the associated receiver signal in in-phase and quadrature channels as generally described above.

The processing unit 2460 is configured to extract additional relevant information about the object as required, for example range information from the phase shift of an incoming phase coded signal within a particular receiver channel 2316a, 2316b. The processing unit 2460 is also configured to analyse the data from the receiver channels 2316a, 2316b, in combination, to extract additional information and/or to further refine the data extracted from each channel 2316a, 2316b individually. The additional/refined information may, for example, include more precise positional information calculated from differential phase delays in the different channels 2316a, 2316b. With an appropriate number of receive antennas positioned appropriately accurate 2D or 3D information may be achieved. It will be appreciated that that the transmitted waveform may take any suitable form, for example one which allows location information to be extracted more precisely, whilst still providing for extraction of micro-Doppler effects. It will be appreciated that the processing unit 2460 may further be configured to extract other information associated with macroscopic object movement including velocity, trajectory, or the like.

The output unit 2318 is configured to convert information extracted from the received signal into a form suitable for review and analysis by an operator of the apparatus. The output unit includes visual and audio units 2480, 2482 for providing visual and audio outputs respectively. The visual unit produces a display dependent on the extracted information and may include, for example positional information, a 2D representation, velocity and/or trajectory information, and any other information relevant to the object and/or any fluctuating component of it. The audio unit 2482 is configured for converting extracted micro-Doppler information into an audible output which varies in dependence on the nature of the variation detected. This is a particularly beneficial feature of the apparatus because it provides an effective increase in the sensitivity of the system. The provision of the audio output means that micro-Doppler effects which cannot be distinguished from noise and/or other effects are not simply filtered out or ignored, as might occur for a crude visual output in which but the audible variations are discarded, but are instead outputted, with the noise, directly to an operator.

Hence, a major advantage of the audio output over more complex signal processing methods is the ability to immediately eliminate clutter that the operator is aware of through his/her other senses by correlation in time; for example, his/her own breathing or movement, gusts of wind, passing traffic, etc. The response time is instantaneous, and in addition the operator does not have to watch a screen all the time but can concentrate on other equipment and be immediately alerted to any change within the building or the like being observed; in particular any sort of motion, from a twitch to a person running. It will be appreciated that the presence of more complex signal processing in the apparatus provides allows optimised use of the apparatus according to requirements. In some cases, for example, information and noise discarded when the signals are converted to a modulated frequency are not completely lost but are, in fact, retained in the apparatus and my be extracted using the more complex signal processing. In some circumstances, human hearing is better able to distinguish variations of interest from background noise than even relatively complex filtering software. For example, small variations which produce regular/recognisable audio patterns can be easily distinguished by a human operator.

Thus, in essence, provision of the audio output allows an operator to become a further processor of the information extracted by the system.

Where the human ear is less sensitive to the variations of interest, for example small variations characterised by a roughly constant repetition rate over a long period (e.g. 30s or more) such as breathing and/or heartbeat signals, the filtering software/circuitry in the processing unit may be configured to filter the signals for enhanced extraction of the variations of interest. For example, the processing unit may implement algorithms which process the raw signals and add extra information to the audio signals output to a user. Hence the ability of the user to detect the signals of interest is further enhanced by, for example, periodic beeps when breathing is detected, or additional chirps to indicate direction of movement.

The apparatus is further be provided with feedback means 2484 for allowing the operator manually to adjust the way in which the processing unit 2460 processes the data and/or the way in which the output from the receiver unit 2316 is converted to the audio frequency. For example, the operator may be provided with means for adding/adjusting filters to filter out or to allow specific frequencies. The operator may be further provided with means for adjusting the range swath processed by the system, for example to home in on a particular object of interest or even to home in on a particular component of the object. Furthermore, where multiple receivers are used the operator may be provided with means for homing in on a two or three-dimensional position of the object of interest.

In order to provide the audio output, the radar output from the processing unit is mixed with an appropriate frequency audio signal in a mixer 2486 to produce the desired audio frequency electrical signal. A transducer/speaker 2488 is provided for transforming the electrical audio signal into audible sound. It will be appreciated that alternatively or additionally the audio output unit 2482 may be provided with a connector (such as an audio jack) for allowing sound transducer means such as headphones, a speaker, or the like to be connected to the audio unit. If the receiver is designed with sufficient sensitivity, the audio output unit 2482 of the output unit may be configured to produce an audio signal which allows sound induced vibrations to be converted back into recognisable sound. For example, the chest movement associated with speech and/or the vibrations induced in a pane of glass or the like by audio frequencies couid potentially be converted to reproduce the sound which created them at the output regardless of the presence of obstacles between the source of the vibrations and the detection apparatus.

Even where the variations of interest do not occur directly as a result of sound (breathing and heart pumping) the audio output may be configured to produce a sound which varies according to the characteristics of the variations, thereby allowing an experienced operator to recognise the source of the variations.

It will be appreciated that once the signal is in the audio domain a number of audio processing techniques may be applied to filter to enhance the presentation of the information to the user, for example the signals from different receiver channels could be processed to provide a stereo output or the like (e.g. surround sound) to give the operator a feel for the direction from which the sound is coming from.

Antenna Array

With reference to Figure 25, there is shown a diagrammatic representation of an antenna array 2500 suitable for use in an embodiment of the invention (including earlier embodiments).

The antenna array 2500 is constructed on a substrate 2502. The substrate may be a block of plastic or glass fibre composite material having a flat supporting surface. In order that embodiments of the invention are available for use where space is restricted, the antenna array is compact, having a peripheral size depending on the arrangement of antenna. For example, the array may comprise an offset transmitter antenna and a trapezoidal receiver array, with the transmitter element comprising a four by two sub-array and each receiver element comprising a two by two sub-array (approximately 70cm x 90cm). Alternatively the array may be arranged .with a central transmitter and four peripheral receivers (approximately 20cm x 30cm). Antenna elements are formed on the supporting surface of the substrate as conductors printed onto the surface. The antenna elements may be dipoles (for example, bow-tie dipoles), TEM horns, microstrip patches, stacked patches, or any other compact element or conductive structure suitable for operating at the required signal frequency.

It will be appreciated that the elements/sub-arrays may not be mounted on a common substrate to minimise weight. In such an arrangement however, the elements/sub-arrays are still mounted in a common plane.

In the embodiment of Figure 25, the array 2500 has four antenna elements in total (only two of which are illustrated in Figure 23 and Figure 24). Three of these elements are first, second, and third receiving elements 2504, 2506, 2508 although other numbers of receiving elements, such as two, three, five or more, may be provided. The fourth element is a transmitting element 2512. The receiving elements 2504, 2506, 2508 are disposed at the vertices of a triangular shaped locus although where four such elements are present (e.g. as described for earlier embodiments) a trapezium-shaped (which may, in a special case be rectangular) locus may be used. With more elements these could be disposed at the vertices say of a trapezoid or an irregular planar locus. In the case of a three-dimensional substrate they may be at the vertices of a cuboid or other solid form. The transmitting element 2512 is disposed at the centre of the same locus. For many applications, the size of the antenna array is preferably kept to a minimum. For example, the spacing between the elements may be in the order of no more than a few half- wavelengths. For example at an operating frequency of 6GHz, spacings may be a few centimetres, say between 1 and 10 cm, preferably between 2 and 8 cm. A hypothetical axis can be considered to extend normal from the supporting surface through the centre of the transmitting element 2512.

As a specific example, if the apparatus is designed for operation with signals of frequency in the region of 6.5 GHz, the antenna elements may be dipoles of approximately 18mm in length, and may be fed with a balanced line feed.

In an alternative form of construction, the antenna elements may be located within a dielectric radome. Associated signal processing circuitry may also be located within the radome in order to provide the apparatus as a self-contained package.

It will be appreciated, however, that the array may comprise any suitable configuration, and where accurate positional information is not required may comprise a single receiver antenna.

Applications There are several useful applications of the detection apparatus. In one such application, the apparatus or a variation on it is used as a through-wall microphone capable of detecting sound induced vibrations indicative of speech or the like.

In another application signs the apparatus or a variation of it is used to detect life-signs such as blood flow, heart pumping/beat, breathing or the like. In such an application the audio output is very beneficial, providing a user with an immediate audible indication of life-signs (including both small (micro-Doppler) and larger gross (Doppler) scale movement) regardless of whether the processing unit of the receiver is sufficiently sensitive to resolve the micro-Doppler effects caused by the variations from other artefacts in the received signal. The ability of the signal to penetrate obstacles is also particularly beneficial in this application because it allows life-signs to be detected in situations where the source of the variations cannot be seen, for example where the source of the variations is the breathing of a human trapped beneath rubble in an earthquake or the like.

In yet another application the apparatus or a variation of it may be used as part of a target classification system to characterise objects according to a 'vibration signature' associated with fluctuating parts of that object.

It will be appreciated that whilst the apparatus is shown and described in terms of operation at a location remote from the detected object and any obstacle obscuring it, the apparatus may alternatively or additionally be configured for placement against the obstacle (such as a wall or the like) to allow detection and analysis of signals reflected from an object obscured by it.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. In particular the features of the systems, apparatus, and/or methods disclosed in one embodiment / implementation / example may be used either independently or in combination with features of the systems, apparatus, and/or methods disclosed in another embodiment / implementation / example.

Claims

1. Radar apparatus for detecting an object in through wall and related applications, the radar apparatus comprising:

means for transmitting radar signals; means for receiving reflected portions of said transmitted signals from said object; wherein said radar apparatus is configured for operation in any of at least a first and a second selectable mode; wherein said transmitting means is configured for transmitting radar signals in accordance with a selected one of said modes of operation, and said receiving means is configured for receiving said reflected portions of said signals transmitted in accordance with said selected mode of operation; and wherein said radar apparatus is configured for transmission of signals, through an obstacle, to said object when operating in at least one of said modes.

2. Apparatus as claimed in claim 1 wherein said radar apparatus is configured for transmission of signals, through an obstacle, to said object, when operating in each of said modes.

3. Apparatus as claimed in claim 1 or 2 wherein said obstacle comprises building material (e.g. wood, stone, plasterboard, concrete, bricks, blocks or the like).

4. Apparatus as claimed in any preceding claim said obstacle comprises building rubble.

5. Apparatus as claimed in any preceding claim said obstacle comprises at least one of a fence, wall, and/or other manufactured partition.

6. Apparatus as claimed in any preceding claim wherein the operating modes are characterised by the form of the transmitted and received radar signals.

7. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit (and/or receive) high bandwidth signals when the radar is operating in at least one (e.g. the first) of said modes.

8. Apparatus as claimed in claim 7 wherein the transmitter (and/or receiver) means is adapted to transmit (and/or receive) ultra-wideband (UWB) signals when in at least at least one (e.g. the first) of said modes.

9. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit (and/or receive) short impulse signals.

10. Apparatus as claimed in claim 9 wherein between 1 and 20 million pulses are transmitted (and/or received) per second.

11. Apparatus as claimed in claim 10 wherein between 2 and 10 million pulses are transmitted (and/or received) per second.

5 12. Apparatus as claimed in claim 11 wherein between 3 and 8 million pulses are transmitted (and/or received) per second.

13. Apparatus as claimed in claim 12 wherein approximately 5 million pulses are transmitted (and/or received) per second.

14. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) is 10 adapted to operate at approximately between 200MHz and 4GHz when in at least one

(e.g. the first) operating mode.

15. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) is adapted to operate at approximately 2 or 3 GHz when in at least one (e.g. the first) operating mode.

15 16. Apparatus as claimed in any preceding claim wherein the radar comprises circuitry adapted to operate in either of the at least two operating modes.

17. Apparatus as claimed in claim 16 wherein the circuitry comprises at least one internal oscillator connectable to a transmitting antenna.

18. Apparatus as claimed in any preceding claim wherein the radar further comprises means 20 for comparing reflected signals received by the receiver means with the transmitted signals.

19. Apparatus as claimed in claim 18 wherein the comparing means is adapted to detect positional information more accurately when the radar is in at least at least one (e.g. the first) of said operating modes relative to at least one other operating mode (e.g. the

25 second).

20. Apparatus as claimed in claim 18 or 19 wherein the comparing means is adapted to compare both the reflected signal and a phase shifted version of the reflected signal.

21. Apparatus as claimed in claim 18, 19 or 20 wherein the comparing means is adapted to compare the reflected signal and a 90 degree phase shifted version of the reflected

30 signal thereby to provide enhanced detection sensitivity.

22. Apparatus as claimed in any of claims 18 to 21 wherein the comparing means is adapted to detect movement information more accurately when the radar is in at least one (e.g. the second) of said operating modes relative to at least one other operating mode (e.g. the first).

23. Apparatus as claimed in any of claims 18 to 22 wherein the comparing means is adapted to provide enhanced range discrimination information when the radar is in at least one operating mode (e.g. a third) relative to at least one other (e.g. the first and/or second) mode.

5 24. Apparatus as claimed in any of claims 18 to 23 wherein the comparing means is adapted to use an IQ (in-phase / quadrature phase) sampling method when processing the reflected signal.

25. Apparatus as claimed in claim 24 wherein the IQ sampling method is adapted to operate both when the radar is in one mode (e.g. the first) and when the radar is in at least one

10 other mode (e.g. the second).

26. Apparatus as claimed in any preceding claim wherein the receiving means comprises a plurality of receiving antennas.

27. Apparatus as claimed in claim 26 wherein the receiving antennas are mounted in an array.

15 28. Apparatus as claimed in claim 26 or 27 wherein the receiving antennas are mounted are mounted in close proximity to one another.

29. Apparatus as claimed in claim 27 wherein the spacing between the arrays is approximately of the order of 10 (say 1 to 20) wavelengths of the centre frequency of operation.

20 30. Apparatus as claimed in claim 27 wherein the arrays are spaced such that the distance between adjacent antennas is of the order of 3 wavelengths of the centre frequency of operation.

31. Apparatus as claimed in any preceding claim wherein the radar further comprises means for measuring the angle of incidence of received reflected signals.

25 32. Apparatus as claimed in claim 31 wherein the measuring means comprises means for measuring the elevation and azimuth angles.

33. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit lower bandwidth signals when the radar is operating in at least one (e.g. the second) mode.

30 34. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit narrowband signals when the radar is operating in at least one (e.g. the second) mode.

35. Apparatus as claimed in any preceding claim wherein the receiver means is adapted to receive narrowband signals when the radar is operating in at least one (e.g. the second) operating mode.

36. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit (and/or receive) a relatively continuous narrowband signal (i.e. with higher than a 50 or 75% duty cycle, preferably a 100% duty cycle) when the

5 radar is operating in at least one (e.g. the second) operating mode.

37. Apparatus as claimed in any preceding claim including circuitry comprising at least two oscillators.

38. Apparatus as claimed in claim 37 wherein the circuitry comprises a stable oscillator for use in generating narrowband signals.

10 39. Apparatus as claimed in claim 38 wherein the stable oscillator is an external oscillator.

40. Apparatus as claimed in claim 37, 38 or 44 wherein the circuitry is adapted to switch between the two oscillators in dependence on the mode of operation of the radar.

41. Apparatus as claimed in any preceding claim wherein the radar is operable in at least a third selectable operating mode.

15 42. Apparatus as claimed in claim 41 wherein the third operating mode is an intermediate operating mode.

43. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit (and/or receive) gated narrowband signals when the radar is in at least one (e.g. the or a third) operating mode.

20 44. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted to transmit (and/or receive) coded narrowband signals when the radar is in at least one (e.g. the or a third) operating mode.

45. Apparatus as claimed in any preceding claim wherein the radar further comprises means for varying a range sweep when the radar operates in at least one (e.g. the or a the third)

25 mode.

46. Apparatus as claimed in claim 45 wherein the range varying means is manually selectable.

47. Apparatus as claimed in claim 46 wherein the range varying means is programmable.

48. Apparatus as claimed in any preceding claim wherein the radar further comprises 30 circuitry adapted to modulate the narrowband signal.

49. Apparatus as claimed in claim 48 wherein the circuitry comprises means for modulating the narrowband signal with a code.

50. Apparatus as claimed in claim 49 wherein the code is in the form of a 32Mbits/sec 1024 bit code.

51. Apparatus as claimed in claim 48, 49 or 50 wherein the modulating means comprises a configurable programmable logic device (PLD).

5 52. Apparatus as claimed in any preceding claim configured for manual selection of operating mode.

53. Apparatus as claimed in any preceding claim configured for automatic selection of operating mode in dependence on whether or not an object is detected in a particular mode of operation.

10 54. Apparatus as claimed in any preceding claim wherein the radar comprises means for processing received signals.

55. Apparatus as claimed in claim 54 wherein the processing means comprises means for post-processing received signals.

56. Apparatus as claimed in claim 54 or 55 wherein the processing means comprises means 15 for analysing the content of reflected narrowband and/or gated or coded narrowband signals.

57. Apparatus as claimed in any of claims 54 to 56 wherein the processing means comprises means for analysing the frequency content of the reflected signals.

58. Apparatus as claimed in any of claims 54 to 57 wherein the processing means comprises 20 means for performing a Fourier transform on the reflected signals.

59. Apparatus as claimed in claim 58 wherein the processing means comprises means for performing a Fast Fourier Transform (FFT) on the reflected signals.

60. Apparatus as claimed in any of claims 54 to 59 wherein the processing means comprises means for performing micro-Doppler analysis on the reflected signals.

25 61. Apparatus as claimed in any preceding claim wherein the processing means is adapted to perform further processing operations on received signals.

62. Apparatus as claimed in claim 61 wherein the further processing operations comprise at least one of wavelet or Bayesian analysis or lag subtraction.

63. Apparatus as claimed in any of claims 54 or 62 wherein the processing means is, at least 30 in part, located externally.

64. Apparatus as claimed in any preceding claim wherein the radar apparatus is portable.

65. Apparatus as claimed in any preceding claim wherein the radar apparatus and all its circuitry are mounted within a single housing capable of transport and operation by a single user.

66. Apparatus as claimed in claim 65 wherein the housing is ruggedised.

5 67. Apparatus as claimed in any preceding claim wherein the radar is adapted to be positioned against an outer wall of a structure to be scanned.

68. Apparatus as claimed in any preceding claim wherein the radar is mountable to a tripod proximate to an outer wall of a structure to be scanned.

69. Apparatus as claimed in any preceding claim wherein the radar is adapted to be 10 positioned approximately between 1 and 20 meters away from an outer wall.

70. Apparatus as claimed in any preceding claim wherein the radar is adapted to be mounted to a vehicle, for example, a land based vehicle and/or an airborne vehicle.

71. Apparatus as claimed in any preceding claim wherein the radar further comprises means for displaying objects detected by the radar.

15 72. Apparatus as claimed in claim 71 wherein the display means is adapted to visually indicate the relative confidence of the detection of an object.

73. Apparatus as claimed in claim 72 wherein the colour of visual indicators on the display may indicate the detection confidence.

74. Apparatus as claimed in claim 71 , 72 or 73 wherein the display is adapted to display the 0 detected object in two and/or three dimensions.

75. Apparatus as claimed in any of claims 71 to 74 wherein the display means is adapted to display the object on a grid.

76. Apparatus as claimed in any of claims 71 to 75 wherein the display means is adapted to display the results of any processing and/or post-processing operations performed on 5 received signals.

77. Apparatus as claimed in any of claims 71 to 76 wherein the display means is adapted to display at least one of the following: the raw signal data; an FFT spectrogram; an "activity" plot; a wavelet analysis plot; a lag subtraction plot; or a "direction" plot.

78. Apparatus as claimed in any preceding claim wherein the radar comprises means for 0 connecting the radar to an external processor (for example, a PC).

79. Apparatus as claimed in any preceding claim wherein the radar comprises means for connecting the radar to a laptop.

80. Apparatus as claimed in any preceding claim wherein the radar apparatus comprises means for connecting the radar to at least a further similar radar apparatus.

81. Apparatus as claimed in any preceding claim wherein the radar apparatus further comprises means for connecting the radar to a remote central processor.

5 82. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted operate mono-statically when the radar is operating in at least one (e.g. the first) of said modes.

83. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted operate bi-statically when the radar is operating in at least one (e.g.

10 the second) of said modes.

84. Apparatus as claimed in any preceding claim wherein the transmitter (and/or receiver) means is adapted operate multi-statically, operating in a mono-static mode or a bi-static mode in dependence on propagation conditions.

85. Apparatus as claimed in any preceding claim configured for detecting movements (e.g. relative movements) of at least a part of an object, the apparatus comprising: means for processing said received signal to detect said movements; and means for generating an audio signal, said audio signal changing dependent on said movements.

86. A radar system for detecting an object in through wall and related applications, the 15 system comprising:

at least two radars comprising apparatus according to any of claims 1 to 85; a central processor adapted to process the outputs of multiple radars; and means for connecting each radar to the central processor.

87. A method of detecting the presence of persons within a structure, behind a wall and/or 20 beneath a collapsed structure using radar apparatus as claimed in any preceding apparatus claim.

88. A method as claimed in claim 87 comprising providing information relating to the layout and content of a structure (for example a building) including the location of static and moving items within the structure.

25 89. A method as claimed in claim 87 or 88 comprising providing information regarding the presence and location of persons within a structure, behind a wall and/or beneath a collapsed structure.

90. A method as claimed in any preceding method claim adapted to be employed in security operations, for example anti-terrorist or hijack situations and in search and rescue operations.

91. A method as claimed in any preceding method claim adapted to provide enhanced object position detection when the radar is in at least one (e.g. the first) mode of operation.

92. A method as claimed in any preceding method claim adapted to provide enhanced 5 tracking capability when the radar apparatus is in at least one (e.g. the first mode) of operation.

93. A method as claimed in any preceding method claim adapted to provide enhanced detection of movement when the radar apparatus is in at least one (e.g. the second) mode of operation.

10 94. A method as claimed in any preceding method claim adapted to provide range discrimination when the radar apparatus operates in at least one (e.g. the or a third mode).

95. A method as claimed in any preceding method claim adapted to begin scanning a structure in the first operating mode.

15 96. A method as claimed in claim 95 adapted to automatically switch to a different mode (e.g. a narrowband mode or a gated narrowband mode) if nothing is picked up during the scanning.

97. A radar system for detecting an object in through wall and related applications, the system comprising:

20 at least two radars each configured for transmission of signals, through an obstacle, to said object; a central processor adapted to process the outputs of each radar; and means for connecting each radar to the central processor.

98. A radar system as claimed in claim 86 or 97 wherein the connecting means is adapted to 25 connect each radar directly to one other.

99. A radar system as claimed in claim 86, 97 or 98 wherein the central processor comprises means for processing the outputs of each radar in the light of the relative position of each radar with respect to an area being scanned.

100. A radar system as claimed in claim 99 wherein the processing means is adapted to 30 process the outputs of each radar in the light of the approximately right angled positioning of the radars with respect to one another.

101. A radar system as claimed in claim 99 or 100 wherein the processing means is adapted to process the outputs of each radar in the light of the orthogonal positioning of the radars with respect to one another.

102. A radar system as claimed in claim 99, 100, or 101 wherein the processing means is adapted to compare the processed outputs of each radar.

5 103. A radar system as claimed in any of claims 99 to 102 wherein the processing means is adapted to process the reflected signals received by the or each radar.

104. A radar system as claimed in any of claims 86 or 97 to 103 wherein the system comprises at least four radars, adapted to be positioned around an area and/or structure to be scanned, with a first pair being positioned in an orthogonal orientation to a second

10 pair.

105. A radar system as claimed in any of claims 86 or 97 to 104 wherein the system comprises a plurality of radar pairs, each radar in the pair being adapted to be positioned in an orthogonal orientation to each other.

106. A radar system as claimed in any of claims 86 or 97 to 105 wherein each radar are 15 adapted to operate in at least one of the following modes: a bi-static mode, a mono-static mode and a multi-static mode.

107. A radar system as claimed in any of claims 86 or 97 to 106 wherein said radars are operable in either a mono-static mode or a bi-static mode in dependence on propagation conditions.

20 108. A radar system as claimed in any of claims 86 or 97 to 107 wherein a pair of said radars are operable bi-statically in dependence on attenuation in a mono-static path to at least one of said radar pair.

109. A radar system as claimed in any of claims 86 or 97 to 108 wherein the radars comprise means for determining position and/or velocity information using coherent integration of

25 successive radar scans thereby to highlight targets moving at specific range rates.

110. A radar system as claimed in any of claims 86 or 97 to 109 wherein the radars are operable for detection of movements having magnitude less than a wavelength of the transmitted signal.

111. A method of scanning a structure using a plurality of radars, each configured for transmission of signals through an obstacle, the method comprising positioning the radars around the structure in an orthogonal orientation to one another, and combining the outputs of the radars.

30 112. A method of scanning a structure using a plurality of radars, each comprising radar apparatus according to any of claims 1 to 85, the method comprising positioning the radars around the structure in an orthogonal orientation to one another, and combining the outputs of the radars.

113. A method of scanning a structure using a radar system as claimed in any of claims 86, or 97 to 110, the method comprising positioning the radars of the radar system around the structure in an orthogonal orientation to one another, and combining the outputs of the radars in said system.

114. Radar apparatus for detecting movements (e.g. relative movements) of at least a part of an object, wherein said movements have magnitude less than a wavelength of signals transmitted by said radar, the apparatus comprising: means for transmitting said radar signals; means for receiving reflected portions of said transmitted signals from said object;

means for processing said received signal to detect said movements; and means for generating an audio signal, said audio signal changing dependent on said movements.

115. Radar apparatus for detecting movements (e.g. relative movements) of at least a part of an object, wherein said radar apparatus is configured for transmission of signals, through an obstacle, to said object, the radar apparatus comprising: means for transmitting said radar signals;

means for receiving reflected portions of said transmitted signals from said object; means for processing said received signal to detect said movements; and means for generating an audio signal, said audio signal changing dependent on said movements.

116. Apparatus as claimed in claim 85 or 114 wherein said radar apparatus is configured for transmission of signals, through an obstacle, to said object.

117. Apparatus as claimed in any of claims 1 to 85, 115 or 116 operable for detection of movements having magnitude less than a wavelength of the transmitted signal.

118. Apparatus as claimed in any of claims 1 to 85 or 115 to 117 operable for detection of movements having magnitude less than half a wavelength of signals transmitted by said radar.

119. Apparatus as claimed in claim 118 operable for detection of movements having magnitude less than a quarter of a wavelength of signals transmitted by said radar.

120. Apparatus as claimed in any of claims 1 to 85 or 115 to 119 wherein said transmitting means is configured to transmit said signal at a frequency below infrared.

121. Apparatus as claimed in claim 120 wherein said transmitting means is configured to transmit said signal at a radio frequency.

122. Apparatus as claimed in claim 121 wherein said transmitting means is configured to transmit said signal at a frequency below 8GHz.

123. Apparatus as claimed in claim 122 wherein said transmitting means is configured to transmit said signal at a frequency between 1 and 4GHz.

124. Apparatus as claimed in claim 121 wherein said transmitting means is configured to transmit said signal at a frequency between 200MHz and 1 GHz

125. Apparatus as claimed in claim 121 wherein said transmitting means is configured to transmit said signal at a frequency of between 8GHz and 25GHz.

126. Apparatus as claimed in claim 125 wherein said transmitting means is configured to transmit said signal at a frequency of substantially 10.125GHz.

127. Apparatus as claimed in claim 125 wherein said transmitting means is configured to transmit said signal at a frequency of substantially 24GHz.

128. Apparatus as claimed in any preceding apparatus claim operable for detection of movements comprising fluctuations in a component of the object.

129. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for extracting micro-Doppler effects from said received signal to detect said movements.

130. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for processing said received signal coherently with respect to the transmitted signal.

131. Apparatus as claimed in any preceding apparatus claim comprising an in-phase and a quadrature channel for IQ processing said received signal.

132. Apparatus as claimed in any preceding apparatus claim wherein said apparatus is operable in a mode in which said transmitted signal comprises a continuous wave.

133. Apparatus as claimed in any preceding apparatus claim wherein said apparatus is operable to transmit multiple carriers, for example at different frequencies

134. Apparatus as claimed in any preceding apparatus claim wherein said apparatus is operable in a mode in which said transmitted signal is coded.

135. Apparatus as claimed in claim 134 wherein said apparatus is operable in a mode in which said transmitted signal is phase coded.

136. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for determining positional information about said object from said received signal.

137. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for determining a range of said object from said received signal.

138. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for setting a range swath.

139. Apparatus as claimed in claim 138 wherein said apparatus is operable to process received signals for objects detected within said range swath only.

140. Apparatus as claimed in claim 138 or 139 wherein said range swath setting means allows automatic setting of said range swath.

141. Apparatus as claimed in any of claims 138 to 140 wherein said range swath setting means allows manual setting of said range swath.

142. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for processing said received signal to determine a 2D position of said object from said detection apparatus.

143. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for processing said received signal to determine a 3D position of said object from said detection apparatus.

144. Apparatus as claimed in any preceding apparatus claim operable to generate an audio signal having a frequency which varies in dependence on detected movement thereby characterising said movement.

145. Apparatus as claimed in any preceding apparatus claim operable to detect movements having a frequency (e.g. vibrations, breathing, heartbeat etc.) wherein at least a component of said audio signal is at said frequency.

146. Apparatus as claimed in any preceding apparatus claim operable to detect movements comprising vibrations caused by sound, and to produce an audio signal characterising said sound.

147. Apparatus as claimed in claim 146 wherein said audio signal is capable of output via a transducer to reproduce said sound.

148. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for converting audio signals generated by the apparatus into sound.

149. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for connecting an audio output device for converting audio signals generated by the apparatus into sound.

150. Apparatus as claimed in any preceding apparatus claim operable to detect movements comprising life-sign indicators and to generate an audio signal characterising said life- sign indicators.

151. Apparatus as claimed in claim 150 wherein said life-signs indicators comprise heart beat indicators.

152. Apparatus as claimed in claim 150 or 151 wherein said life-signs indicators comprise movements indicative of breathing.

153. Apparatus as claimed in any preceding apparatus claim, said apparatus comprising means for processing said received signal to provide a characteristic signature of said movements.

154. Apparatus as claimed in any preceding apparatus claim operable to generate a plurality of audio signals configured for providing a stereo output.

155. Apparatus as claimed in claim 153 wherein said audio signals are configured for providing said stereo output in dependence on corresponding signals received in a plurality of receive channels.

156. Apparatus as claimed in any preceding apparatus claim comprising means for generating an audio signal, wherein the generating means comprises part of output apparatus; said output apparatus comprising: means for converting an output signal from said radar apparatus into an audio frequency signal characterising detected movements.

157. Apparatus as claimed in claim 156 wherein said conversion means comprises a mixer for mixing said radar output with audio output to produce said audio signal.

158. Apparatus as claimed in claim 156 or 157 wherein said conversion means further comprises a transducer for converting said generated audio signal into sound.

159. Apparatus as claimed in any of claims 156 to 158 wherein said conversion means further comprises means for connecting a transducer for converting said generated audio signal into sound.

160. Apparatus as claimed in any preceding apparatus claim wherein said apparatus is configured for detecting life-signs through obstacles by processing said received signal to detect movements (e.g. breathing, heartbeat, sound induced vibrations etc.) indicative of said life-signs.

161. Apparatus as claimed in any preceding apparatus claim wherein said apparatus is configured:

for remotely detecting oscillations and/or vibrations caused by sound; for processing said received signal to extract audio frequency vibrations of at least a part of said object; and for generating an audio signal, said audio signal changing dependent on said oscillations and/or vibrations.

162. Apparatus as claimed in any preceding apparatus claim configured for operation at a location remote from an obstacle (e.g. a wall) obscuring the object.

163. Apparatus as claimed in any preceding apparatus claim configured for operation against an obstacle (e.g. a wall) obscuring the object.

164. Apparatus for detecting life-signs through obstacles; means for transmitting a signal; means for receiving a signal reflected from an object, said received signal comprising at least part of said transmitted signal; and means for processing said received signal to detect movements (e.g. breathing, heartbeat, sound induced vibrations etc.) indicative of life-signs; wherein said apparatus is configured for transmission of said transmitted signals, through an obstacle obscuring a source of said life-signs.

165. Apparatus for remotely detecting oscillations and/or vibrations caused by sound, the apparatus comprising: means for transmitting a signal; means for receiving a signal reflected from an object, said received signal comprising at least part of said transmitted signal; means for processing said received signal to extract audio frequency vibrations of at least a part of said object; and

means for generating an audio signal, said audio signal changing dependent on said oscillations and/or vibrations.

166. Apparatus for detecting movements (e.g. relative movements) of at least part of an object, the apparatus comprising: means for transmitting a signal;

means for receiving a reflected portion of said transmitted signal from said object;

means for processing said received signal to detect said movements; and means for providing an output characterising said movements directly to a user;

5 wherein said output changes in dependence on the movements; and wherein said apparatus is configured for transmission of said transmitted signals, through an obstacle, to said object.

167. A radar system comprising at least one radar apparatus according to any preceding apparatus claim and means for connecting the radar to an external processing device.

168. A method of detecting life-signs through obstacles using apparatus as claimed in any preceding apparatus claim, the method comprising: processing said received signal to detect movements (e.g. breathing, heartbeat, sound induced vibrations etc.) indicative of life-signs.

10 169. A method of remotely detecting oscillations and/or vibrations caused by sound using apparatus as claimed in any preceding apparatus claim the method comprising processing said received signal to extract audio frequency vibrations of at least a part of said object; and generating an audio signal, said audio signal changing dependent on said oscillations and/or vibrations.