EP1814197A1

EP1814197A1 - An antenna arrangement having unevenly separated elements

Info

Publication number: EP1814197A1
Application number: EP06425031A
Authority: EP
Inventors: Carlo Buoli; Simone Pietro Garlaschelli; Stefano Dr. Verzura
Original assignee: Siemens SpA
Current assignee: Nokia Solutions and Networks SpA
Priority date: 2006-01-24
Filing date: 2006-01-24
Publication date: 2007-08-01
Anticipated expiration: 2026-01-24
Also published as: ES2334937T3; EP1814197B1; ATE447778T1; DE602006010168D1

Abstract

An antenna arrangement (10) includes transmitting elements (18) for a transmitted signal and a receiving elements (18) for received signal. The transmitting and receiving elements (18) are arranged in respective linear arrays. The arrays of transmitting elements and receiving elements are separated unevenly to produce, at each array of receiving elements, destructive interference of the signal transmitted from two neighboring arrays of transmitting elements.

Description

Field of the invention

The invention relates to antenna arrangements, and was developed with specific attention paid to its possible application to the type of arrangement known as Outdoor Device Unit (ODU).

Description of the related art

Antenna arrangement of current use (e.g. in terrestrial radio links, such as those supporting the "fixed" infrastructures of mobile radio networks) have to properly deal with a number of operational requirements.
These requirements include the pointing ability of the antenna, namely the possibility of properly directing the main lobe(s) of the radiation diagram of the antenna. Typically, pointing is performed manually by an expert technician. The antenna arrangement (e.g. ODU) must have a solid, rigid structure adapted to be oriented in order to achieve the desired pointing and retein such pointing.
Additionally, present-day antenna structures are comprised of several modules (antenna proper, pole mounting, and so on). For "low" frequencies (i.e. 2 GHz) distributed antennas are used, including a number of elements that operate in a space diversity configuration and are not arranged on the same substrate. These solutions are not economically convenient for higher frequency bands.
In general terms, assembling and installing an antenna must be simple and economical processes, and (especially in urban environments) the antenna should be as little obtrusive as possible, even from an aesthetical viewpoint.
At the same time, the performance level (e.g. antenna gain, crosstalk between transmitter and receiver sections) should not be adversely affected by any attempts at complying with the other requirements indicated in the foregoing.

Object and summary of the invention

The object of the invention is thus to provide a fully satisfactory response to those needs.
According to the present invention, that object is achieved by means of an antenna arrangement having the features set forth in the claims that follow. The claims are an integral part of the disclosure of the invention provided herein.
A preferred embodiment of the arrangement described herein allows an easier installation, by means of a "smart" antenna integrated in a ODU and adapted to manage automatic software-driven antenna pointing. Preferably, the related structure is compact as it includes radio circuitry and the antenna elements proper arranged on the same printed circuit board. The related assembly procedures can thus be made simpler by resorting, e.g., to a standard SMT process. The arrangement is of reduced size overall, this being particularly the case in point for operating frequencies higher than 15 GHz.
Essentially, the preferred embodiment of the antenna arrangement described herein entails i.a, the following advantages:

the assembly process of the antenna is made significantly easier, as it becomes very similar to a standard process for mounting integrated circuits (ICs) onto a printed circuit board (PCB) by resorting e.g. to Surface Mounting Devices (SMD) technology;
automatic software-driven antenna pointing is made possible: a software module drives the beam forming process of the antenna with the possibility of tracking a main signal and minimizing side lobes to minimize interferences;
manufacturing the antenna becomes economically convenient due to an optimized process and the need of a single board development; and
a duplexer filter proper can be dispensed with.

Brief description of the annexed drawings

The invention will now be described, by way of example only, with reference to the enclosed figures of drawing, wherein:

Figure 1 is front elevational view of an antenna arrangement as described herein;
Figure 2 is a cross sectional view along line II-II of Figure 1;
Figure 3 is an enlarged view of the portion of Figure 2 indicated by arrow III;
Figure 4 is representative of the architectural arrangement of transmitting and receiving elements in the antenna described herein;
Figure 5 is a functional block diagram representative of the antenna arrangement described herein;
Figures 6 and 7 are block diagrams of transmitting and receiving circuitry associated with the antenna arrangement described herein; and
Figure 8 details the deployment of transmitter/receiver slots in the antenna arrangement described herein.

Detailed description of preferred embodiments of the invention

An antenna arrangement 10 as described herein is essentially in the form of a self-contained unit, e.g. a flat panel having preferably a square/rectangular shape. Other shapes (e.g. round, diamond shaped with rounded corners and so on are possible but less preferred.
Typical dimensions for an antenna operating in the 18 GHz range are about 30 cm x 30 cm, while a typical weight of the assembly is about 2 kg, which makes it very practical to transport and/or hoist to mounting sites.
In structural terms, the antenna arrangement 10 includes a core layer 12 having associated a cover lid 14. The core layer 12 is essentially comprised of a standard printed circuit board (PCB) having mounted thereon various components 16 that implement - in a manner known per se - typical radio functions (e.g. DC converter, modem, digital processing, and IF/RF conversion).
The components 16 can thus be mounted on the PCB 12 (typically on the top surface thereof, which in fact corresponds to the rear side of the antenna 10) by resorting to any standard process known from printed circuit/integrated circuit technology. Standard Surface Mounting Technology (SMT) representes a presently preferred choice for such mounting technology. In figure 3, reference 16a designates conductive lines or strips extending at the top surface of the (possibly multilayered) PCB 12 to provide electrical connections to the circuits 16.
The cover 14 is mounted onto the top surface of the PCB and retained thereon by known means such as e.g. screws. The cover 14 is typically of a lightweight, electrically conductive material and is thus able to shield electromagnetic emission from the circuits 16, while also protecting the circuits 16 from electromagnetic interference from outside. Preferably the cover 14 includes niches and/or ribs, that, while reducing interference among microwave functions, also bestow the desired mechanical robustness on the antenna arrangement 10. Laterally (e.g. at the edge) of the cover 14, connectors 15 for IDU-ODU links (not shown) are provided.
On the bottom side of the PCB 12 (which in fact corresponds to the front side of the antenna 10) a matrix of slots 18 is provided. The enlarged view of Figure 3 shows a number of metallization layers 20, 22, and 24 provided on the bottom side of the PCB 12 and having associated electrically insulating layers 20a, 22a, and 24a. Specifically, the metallization layer 20 is a ground plane to separate the antenna elements 18 from the circuitry 16. The metallization layer 22 is comprised of signal carrying lines or strips shaped to act as feeders to/from the slots 18 that are provided in the layer 24.
As better illustrated in Figure 1, the slots 18 are arranged in a plurality of sub-matrixes or subsets. In the esemplary embodiment shown herein, four sub-matrixes of slots designated 18A, 18B, 18C, and 18D are shown roughly arranged in two rows and two columns. Thanks to the arrangement of the slots 18 in a plurality of sub-matrixes 18A to 18D, the antenna 10 can be implemented as a "smart" integrated antenna.
Each sub-matrix 18A, 18B, 18C, and 18D includes both transmitting and receiving slots. Specifically, each sub-matrix 18A, 18B, 18C, and 18D can be considered to be comprised of alternated columns (or, possibly, rows) of receiving and transmitting slots. In the exemplary embodiment shown, each sub-matrix 18A, 18B, 18C, and 18D is comprised of four columns of four slots each. The "odd" columns (i.e. the first and third columns) may thus be comprised of receiving slots while the "even" columns (i.e. the second and fourth columns) may be comprised of transmitting slots.
Those of skill in the art will promptly appreciate that such an alternate arrangement of receiving and transmitting slots may be applied to i) any number of columns, and ii) to the rows, in the place of the columns, in the sub-matrixes 18A, 18B, 18C, and 18D. Additionally, these sub-matrixes may present in any number other than four, including (insofar as the alternate arrangement of receiving and transmitting slots 18 in the antenna 10 is considered) the possible presence of a single matrix of slots 18.
Figure 1 is a schematic representation of the slot arrangement, wherein the receiving and transmitting slots 18 are shown with uniform spacings for the sake of simplicity. In fact, as better explained in the following in connection with Figure 8, such spacings are selected to be non-uniform in order to separate the transmitting and receiving sections of the antenna 10 while dispensing with the need of using a duplexer for that purpose.
The arrangement described herein thus provides an integrated microwave outdoor unit (ODU) consisting of a radio appliance with integrated antenna elements (i.e. the slots 18), implemented on a printed circuit board 12, having mounted thereon the radio function components (essentially the circuitry 16) and the pole mounting attacks (these are not expressly shown, but can easily be provided on the cover 14). The availability of a plurality of sub-matrixes 18A, 18B, 18C, and 18D of antenna elements 18 makes the antenna suitable for the application of a beam forming mechanism in view of automatic pointing of the antenna system.
In many applications, integrated antennas are used, particularly in the military field e.g. for radar tracking/ranging applications and for missile guiding or in the commercial field for low frequency radio applications. Differently from these prior art applications, the basic concept underlying the arrangement described herein is to employ a PCB antenna integrated in a radio link appliance operating at microwave frequencies. This while using a Frequency Division Domain (FDD) approach, which admits full-duplex operation while also ensuring good insulation performance between the receiver and transmitter sections with good system gain.
The microwave transmitters and receivers (included in the circuitry generally indicated as 16 in Figures 2 and 3) are distributed over the PCB 12 in sections corresponding to the sub-matrixes of slots 18. For instance, in the exemplary arrangement described herein, the microwave transmitters and receivers are distributed over the PCB 12 in four "quadrants". Each such section or quadrant (for instance, figure 4 illustrates the quadrant corresponding to the slot sub-matrix 18A) includes a transmitter 30A and a receiver 40A. These are connected to the slots 18 via the lines 22 (see also Figure 3) so that the transmitter 30A feeds the transmitting slots with the signal to be transmitted and the receiver 40A is in turn fed with the signal received from the receiving slots. Typically, both the signal transmitted and the signal received include "in-phase" and "quadrature" components, designated I and Q, respectively.
The transmitter 30A and the receiver 40A are connected to several slots 18 in order to reach the desired gain of the antenna while also allowing "beam forming" operation. This is carried out by known means and methods, thus making it unnecessary to provide a more detailed description herein.
Figure 5 is a functional block diagram of signal processing circuitry adapted to be incorporated in the circuitry 16 mounted on board the PCB 12. Specifically, the circuitry in question includes a modem 32 operating under the control of a microprocessor 34 (which manages alarms, performance monitoring and beam forming processes) and cooperating with a power supply unit 36 (which distributes secondary and tertiary bias voltages).
The block 38 is a de-phasing unit included in a digital device such as, e.g., a FGPA (Field Programmable Gate Array) to act on the signals transmitted and received via the antenna by dephasing them in order to correspondingly modify the antenna transmission/reception lobe(s) to effect proper antenna pointing. The principles and criteria that dictate operation of the block 38 and the circuit 380 are well known to those of skill in the art, thus making it unnecessary to provide a more detailed description herein.
On the transmission side, signals transmitted by the modem 32 are processed by Digital/ Analog converters 34A, 34B, 34C, and 34D to be then up-converted for transmission by the transmitters 30A, 30B, 30C, and 30D. On the reception side, signals received via the receivers 40A, 40B, 40C, and 40D, are down-converted and then processed via Analog/ Digital converters 36A, 36B, 36C, and 36D to be then fed to the modem 32.
The suffixes A, B, C, and D evidently denote the respective components for the various sub-matrixes of slots 14A, 14B, 14C, and 14D. Up-conversion in transmission and down-conversion in reception are performed by means of microwave units of a known type that were de facto considered as incorporated in the corresponding transmitters/receivers.
In the currently preferred embodiment of the arrangement described herein, the microwave functions are distributed over the PCB 12 as this facilitates reducing the manufacturing cost of the whole antenna arrangement.
This is particularly true for the transmitter (e.g. the transmitter 30A shown in Figure 4) as demonstrated by the block diagram of Figure 6: there the "I" and "Q" components of the baseband signal are directly up-converted by mixing in a mixer stage 50 with a local reference signal obtained by multiplying in a multiplier 52 a local reference signal OLRF. The resulting up-converted signal is power amplified in a RF amplifier 56, while a variable attenuator 54 manages the output power level.
An exemplary block diagram of the receiver (e.g. the receiver 40A shown in Figure 4) is shown in Figure 7. This includes a low noise amplifier (LNA) 60 connected to the slots 18, which amplifies the signal received and brings it to a mixer 62. The mixer 62 is "pumped" by a local reference signal obtained by multiplying in a multiplier a local reference signal OLRF,. In fact the "pump" signal of the mixer 62 can be the same signal generated by the multiplier 52 of the transmitter section that is a local multiplied oscillator signal, coming from a common microwave oscillator. The "I" and "Q" converted signals from the mixer 62 are then combined by means of a 90 hybrid element 64 and converted again to a base band (BB) signal by using a common PCB mixer 66 fed with a desired local shifter signal OL.
As indicated in the foregoing, each sub-matrix 18A, 18B, 18C, and 18D is comprised of alternated columns (or, possibly, rows) of receiving (RX) and transmitting (TX) slots 18 to optimize RX/TX separation.
As schematically shown in figure 8, the distances A and B between alternated receiver and transmitter elements 18 is adjusted so that the arrays (e.g columns) of receiving (RX) slots 18 - more precisely, the notional median lines thereof, orthogonal to the direction of extension of the slots 19 - are not arranged midway the arrays (e.g columns) of transmitting (TX) slots 18.
As shown in figure 8, the arrays of receiver and transmitter elements 18 are arranged in such a way that the notional median line of each array of receiving slots RX has two distances A and B to the median lines of the two neighboring transmitting slots TX. The two distances A and B are not equal - as it would be the case for equally spaced receiving and transmitting arrays - but rather have a difference (A - B) of about λ/2. The entity λ is representative of the (central) wavelength used for transmission and reception (corresponding to e.g. 24.43 GHz or 26.57 GHz).
Referring to "about" λ/2 is intended to take into account that, due to the geometry of the slots, the optimum value of A - B may in fact slightly differ from the exact mathematical value λ/2.
This uneven spacing or separation (i.e. A - B being different from 0) of the arrays of receiving and transmitting slots (RX and TX, respectively) provides proper isolation between transmitting and receiving slots. This without having to resort for that purpose to a duplexer as an additional component of the antenna arrangement and/or to cross polarization between signals transmitted and received.
In fact, by referring to figure 8, it will be appreciated that - if the antenna is used for simultaneously transmitting and receiving signals - the array of receiving elements designated RX will be exposed to respective components of the signal transmitted from the two neighboring arrays of transmitting elements designated TX.
However, the difference A - B being (at least approximately) half the wavelength λ, the two components from the two neighboring arrays of transmitting elements TX will interfere with maximum destructive interference (being in fact opposed in phase) in correspondence with the array of receiving elements RX. Interference between the signal transmitted and the signal received is thus minimized by providing a very good level of separation between the two thus making it unnecessary to include a duplexer in the antenna arrangement.
Those of skill in the art will promptly appreciate that the uneven spacing just described will also minimize interference of the signal received on the signal transmitted.
Some preliminary experiments performed by the Applicants indicate typical values of transmission (i.e. crosstalk) between adjacent transmitting and receiving slots in the range of -45 to -70 dB, fully confirm the possibility of avoiding duplexer filters for receiver and transmitter decoupling.
Consequently, without prejudice to the underlying principles of the invention, the details and the embodiments may vary, even appreciably, with reference to what has been described by way of example only, without departing from the scope of the invention as defined by the annexed claims.

Claims

An antenna arrangement (10) including transmitting elements (18) for a transmitted signal and receiving elements (18) for a received signal, wherein said transmitting (TX) and receiving (RX) antenna elements (18) are arranged in respective arrays, said arrays of transmitting and receiving antenna elements being separated unevenly to produce, at least one array of receiving elements (RX), , destructive interference of said transmitted signal as transmitted from two neighboring arrays of transmitting elements (TX).
The arrangement of claim 1, characterized in that said unevenly separated arrays of transmitting (TX) and receiving (RX) antenna elements include at least one array of receiving (RX) elements having two different distances (A, B) to two neighboring arrays of transmitting (TX) elements.
The arrangement of claim 2, characterized in that said two different distances (A, B) have a difference (A - B) of about half (λ/2) said wavelength (λ).
The arrangement any of the previous claims, characterized in that said transmitting and receiving antenna elements (18) are in the form of slots.
The arrangement of any of the previous claims, characterized in that said arrays of transmitting and receiving antenna elements (18) are linear arrays having notional median lines and said uneven separation is defined between respective median lines of said linear arrays of transmitting and receiving antenna elements (18).
The arrangement of any of the previous claims, characterized in that said transmitting and receiving antenna elements (18) are in the form of slots and said arrays of transmitting and receiving antenna elements (18) are linear arrays extending orthogonal to the direction of extension of said slots (18).
The arrangement of either of claims 5 or 6, characterized in that said linear arrays are the columns of at least one matrix (18A, 18B, 18C, 18D) of said transmitting and receiving elements (18).
The arrangement of any of the previous claims, characterized in that said antenna elements (18) are arranged in subgroups (18A, 18B, 18C, 18D) having associated respective sets of signal processing circuitry (30A, 34A, 36A, 40A; 30B, 34B, 36B, 40B; 30C, 34C, 36C, 40C; 30D, 34D, 36D, 40D) thereby permitting automatic pointing of the antenna (10) via signal processing (38).
The arrangement of any of the previous claims, characterized in that it includes a core layer (12) in the form of a printed circuit board carrying said antenna elements (18) as well as signal processing circuitry (16) associated therewith.
The arrangement of claim 9, characterized in that said antenna elements (18) and said associated circuitry (18) are located at opposite sides of said printed circuit board (12).
The arrangement of either of claims 9 or 10, characterized in that said associated circuitry (16) includes SMD components mounted on said printed circuit board (12) using surface mounting technology (SMT).
The arrangement of any of claims 9 to 11, characterized in that said antenna elements (18) are provided in the form of slots in a metallization (24) on said printed circuit board (12).
The arrangement of any of claims 9 to 12, characterized in that it includes a metallization layer forming a ground plane on said printed circuit board (12) to separate said antenna elements (18) from said associated circuitry (16).
The arrangement of any of claims 9 to 13, characterized in that it includes metallized lines or strips (22) provided on said printed circuit board (12) to convey signals with respect to said antenna elements (18).
the arrangement of any of claims 9 to 13, characterized in that it includes a de-phasing unit (38) managed by a microprocessor (34) to act on the signals transmitted and received via the antenna by dephasing them in order to correspondingly modify the antenna transmission/reception lobe(s) to effect proper antenna pointing
The arrangement of any of the previous claims, characterized in that it includes a core layer (12) carrying said antenna elements (18) as well as signal processing circuitry (16) associated therewith, said core layer (12) having associated a cover (14) acting as a shield for said associated circuitry (16).
The arrangement of any of the previous claims, in the form a self-contained unit.
The arrangement of any of the previous claims, in the form of a flat panel.
The arrangement of any of the previous claims, characterised in that said flat panel has square or rectangular shape overall.