WO2001008259A1

WO2001008259A1 - Reconfigurable active phased array

Info

Publication number: WO2001008259A1
Application number: PCT/US2000/019828
Authority: WO
Inventors: George S. Hardie
Original assignee: Fujant, Inc.
Priority date: 1999-07-22
Filing date: 2000-07-21
Publication date: 2001-02-01

Abstract

A reconfigurable active phased array distributes RF signals to an array of active antenna elements, each of which incorporates medium-power amplifiers and phase shifters. A switching network is configurable to distribute any of the RF signals to any of the active antenna elements. Phase shifters are provided for each active antenna element and are configurable to adjust the radiation pattern for the antenna array. Sensors detect signal power levels throughout the system to automatically reconfigure the signal distribution and phase shifts in response to component failures, changes in inbound traffic and other criteria.

Description

RECONFIGURABLE ACTIVE PHASED ARRAY

The present invention relates to communications systems and, more specifically, to a reconfigurable system for distributing signals using an array of active antennas.

BACKGROUND OF THE INVENTION

Wireless communications systems provide voice, data and other information services via portable devices such as cellular telephones and personal communications services ("PCS") equipment. Communications with the portable devices is accomplished using radio frequency waves. In a typical system, radio frequency ("RF") transmitters and receivers in the portable devices communicate with RF receivers and transmitters in stationary base-stations. The stationary base-stations, in turn, establish a connection (typically via a public switched telephone network "PSTN") to an endpoint that provides the desired information service. This endpoint may be another telephone, a computer or some other information resource. Wireless communications systems such as cellular telephone systems use a distributed base-station network to provide service over a wide geographical area. Each base-station transmits RF waves to and receives RF waves from the devices operating within the immediate geographical area. The size and shape of this area, known as a cell, is defined, in part, by the radiation pattern of the base-station antenna. Typically, the radiation pattern of each base-station overlaps the radiation patterns of adjacent base-stations to some extent to ensure that there are no "gaps" between the cells. Thus, in the aggregate, the distributed grid of base-stations may provide seamless cellular service over a wide geographical area. See, for example, U.S. Patent No. 5,596,329 to Searle et al.

To generate the RF waves, the signals associated with each inbound call from the PSTN are used by the base station to modulate an RF signal, or carrier. One RF carrier may be modulated by more than one call, and a variety of modulation schemes have been developed to allow multiple calls to be modulated on a single carrier. To handle a sufficient volume of inbound calls, more than one carrier may be required. These carriers are separated in frequency. For example, the information for several calls may be modulated on a RF carrier with a center frequency of 1.9571 GHz, while the information for another set of calls may be modulated on a second RF carrier with a center frequency of 1.9577 GHz.

An RF transmitter in a base-station must be capable of broadcasting a relatively powerful RF signal to effectively communicate with multiple portable devices located within the service area of the transmitter. Some conventional transmitters use a single high-power amplifier for amplifying all of the signals broadcast by the transmitter. The transmitter combines the RF signals before the amplification stage and amplifies the combined signals. These amplified signals are routed to an antenna to generate the RF waves. In certain circumstances, this type of transmitter may provide high-power at a relatively low cost. To achieve various RF wave broadcast obj ectives, techniques are known for manipulating the signals in RF broadcast systems. For example, methods are known for varying the radiated RF wave pattern of a given signal. Certain aircraft systems use arrays of antenna elements with phase shifters that can adjust the phase of the signals for each element of the array. These systems adjust the radiation pattern as the aircraft rolls by adjusting the phase shifts. See U.S.

Patent No. 4,882,587 to Vodopia. Methods are also known for switching multiple input signals to multiple antennas to distribute the input signals based on various system performance objectives. See, for example, U.S. Patent No. 5,550,550 to Das, U.S. Patent No. 5,289,193 to Lenormand et al. and U.S. Patent No. 5,204,686 to Petrelis et al. There is a need to improve conventional wireless communications systems such as those discussed above to provide more efficient and reliable communication. For example, some conventional systems are inefficient because they must reduce power to transmit multiple channels. Also, transmitters that use a single high-power amplifier may incur relatively high power losses in the cable that connects the high-power amplifier to the antenna. Although low- loss cable may be used to offset these power losses, low-loss cable is relatively expensive.

Moreover, systems that use high-power amplifiers may be less reliable. The high-power operating conditions to which these amplifiers are subjected typically cause significant stresses on the amplifier components. This increases the likelihood of an amplifier failure. Typically, once an amplifier fails, all of the channels associated with that amplifier will be disrupted. There also is a need for an efficient method of adjusting antenna radiation patterns for cellular and PCS base-stations, particularly in view of the dynamic nature of the traffic that is distributed through the base-stations. In summary, a need exists for a more efficient and more reliable transmission system for wireless communications systems.

SUMMARY OF THE INVENTION

An RF transmission system constructed according to one embodiment of the invention broadcasts modulated RF signals using a configurable array of active antenna elements. Each active antenna element includes a medium-power amplifier, a phase shifter and a radiating element. The system includes a switching network and phase shifters to distribute input RF signals to the active antenna elements and to define the shape of the RF radiation patterns generated by the antenna array. Provisions are made for dynamically reconfiguring the system to improve the efficiency of the transmitter, to compensate for system failures and to modify the RF radiation patterns.

The switching network selectively distributes input RF signals to the active antenna elements in the array. In one embodiment, the system may be configured to broadcast any of the input RF signals using any of the active antenna elements. Significantly, the configuration of the switching network may be modified as needed to change the distribution of the RF signals.

The phase shifters in each of the active antenna elements may be used to adjust the radiation pattern for the antenna array. In one embodiment, the phase of the RF signal associated with each active antenna element may be independently controlled. Thus, the radiation pattern for the site may be precisely tailored to the site requirements. Moreover, by coordinating the configuration of the switching network and the phase shifter settings, the invention provides an effective technique for dynamically compensating for changes that occur within the transmission system related to, for example, dynamic signal traffic, component failures and site reconfigurations .

In one embodiment, the system automatically alters the configuration of the system in response to changes that occur within the system. For example, the system may detect RF signal power levels at several stages in the transmitter and automatically reconfigure the signal distribution and phase shifts accordingly. In one case, sensors connected to the RF signal input lines detect whether the inbound RF signals are active or inactive. In response, the system may reconfigure the distribution of the corresponding RF signals to the active antenna elements so that each of the RF signals is transmitted at a comparable output power level. In addition, sensors in the system may detect failures in the system components. In this case, the system may reconfigure the distribution of the RF signals so that the signals previously routed to the failed components are routed to other components. In either case, the system also may adjust the phase shifts as discussed above. In one embodiment, the invention uses a priori switch and phase- shifter settings to adapt to the channel traffic and to compensate for the component failures. The invention thus provides a useful and reliable final amplifier and antenna for transmitters in wireless communications systems such as PCS and cellular telephone systems. The reconfigurable switching network partitions the active antenna array to adapt to channel traffic. The reconfigurable phase shifters provide beam shaping to automatically tailor the beam shape of the antenna array to site specific requirements as the partitioning of the array changes. Accordingly, an active antenna system for distributing radio frequency signals may include a switching network for distributing a plurality of radio frequency signals to a plurality of active antenna elements that produce radio frequency waves from the radio frequency signals, and an array configuration controller that is responsive to an indication to change the distribution of the radio frequency signals to the active antennas, where the array configuration controller cooperates with the switching network to reconfigure the distribution of the radio frequency signals.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become apparent from the following description and claims, when taken with the accompanying drawings, wherein similar reference characters refer to similar elements throughout and in which:

FIGURE 1 is a block diagram illustrating general operations of one embodiment of a reconfigurable active phased array constructed according to the invention;

FIGURE 2 is a block diagram illustrating one embodiment of a reconfigurable active phased array constructed according to the invention;

FIGURES 3A and 3B are graphical representations of exemplary radiation patterns produced by the system of FIGURE 2;

FIGURE 4 is a block diagram illustrating another embodiment of a reconfigurable active phased array constructed according to the invention that incorporates a digital feed network;

FIGURE 5 is a flowchart illustrating operations that may be performed by the system of FIGURE 4;

FIGURE 6 is a block diagram illustrating one embodiment of an RF power module constructed according to the invention; FIGURE 7 is a block diagram illustrating one embodiment of a digital signal processor implementation according to the invention;

FIGURE 8 is a block diagram illustrating one embodiment of switch and phase configuration components constructed according to the invention;

FIGURE 9 is a flowchart illustrating operations that may be performed by the system of FIGURE 8; and

FIGURE 10 is a block diagram illustrating one embodiment of a communications system incorporating a reconfigurable active phased array according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS FIGURE 1 illustrates basic operational components of one embodiment of the invention.

An RF transmission system S broadcasts incoming RF signals 20 (as represented by the RF signals lines 20 depicted in the upper left portion of FIGURE 1) using an array of active antenna modules 22 (right). The system S includes a switching network 24 and phase shifters 26 to control the distribution of the RF signals 20 to the array and to define the radiation patterns for the system S. Both the switching network 24 and the phase shifters 26 can be reconfigured, as needed, to change the signal distribution and the antenna radiation patterns.

The switching network 24 distributes the input RF signals 20 to several subarrays 28 (e.g., subarray 1, subarray 2, ... subarray N), each of which includes one or more active antenna modules 22. To reduce the complexity of FIGURE 1 , the details of the subarrays 28 are depicted only for subarray 1. The system S routes each of the RF signals 20 to an antenna subarray 28 independently of the other RF signals 20. For example, in one embodiment each subarray 28 is connected to receive only one of the RF signals 20. However, a given RF signal 20 may be routed to one, all or none of the subarrays 28. Typically, the switching network 24 is configured so that an equal number of subarrays 28 are assigned to each of the RF signals 20, when possible. Each active antenna element 22 includes a phase shifter 26, an amplifier 30 and a radiating element 32. The amplifiers 30 may be medium-power amplifiers, rather than the high- power amplifiers that are used in many conventional systems. To provide a high-power output for a given RF signal 20, the system S routes the RF signal 20 to multiple amplifiers 30. For example, an RF signal 20 may be routed to one or more of the subarrays 28, where each of the subarrays 28 includes several medium-power amplifiers 30.

A unique phase may be defined for each radiating element 32 by dynamically controlling the phase shift induced by each of the phase shifters 26. Thus, the phase shift for each radiating element 32 may be set independently of the phase shift setting for any of the other radiating elements 32; even for those radiating elements 32 that are transmitting the same RF signal 20 (e.g., radiating elements 32 within the same subarray 28).

An array configuration controller 34 manages the settings of the switching network 24 and the phase shifters 26. In one embodiment, the settings are specified by a priori settings stored in a data memory (not shown). The system S also includes detectors (e.g., traffic activity detectors 36 and component failure detectors 38 and 39) that sense changes in the operating conditions of the system S. In response to these changes, a switch configuration controller 40 and a phase shift controller 42 (lower left) may change the switching network settings and the phase shifter settings, respectively. The switching network and phase shifter settings also may be altered in response to signals from external systems (not shown).

With the above overview in mind, FIGURE 2 illustrates one embodiment of a system S constructed according to the invention. The system S receives several modulated RF signals from a signal source (not shown) via RF signal lines 20. For convenience, reference characters within a group (e.g., 20A, 20B, etc.) may be collectively referred to herein as the base number (e.g., 20). Through a network of power dividers 44 and switches 46, the system S distributes the RF signals to several subarrays of active antennas 28. In FIGURE 2, the switching network 24 discussed in FIGURE 1 is implemented as a bank of five power dividers 44 and a bank of five 1x5 switches 46 (upper left). To reduce the complexity of FIGURE 2, only two of the power dividers 44 and the switches 46 are shown. In general, components not depicted are indicated by ellipses. The array configuration controller 34 of FIGURE 1 is implemented as a digital logic circuit: switch and phase shifter logic 48 (lower left). To further reduce the complexity of FIGURE 2, many of the peripheral components of atypical system, including driver amplifiers, cable runs up to the antenna, the antenna power supply and the antenna cooling means, are not shown. The system of FIGURE 2 handles up to five concurrent input RF signals on the five RF signals lines 20. In general, the input RF signals (referred to hereafter for convenience simply as RF signals 20, 20A, etc.) are associated with independently modulated RF carrier signals. The input RF signals 20 may or may not be active simultaneously due to call traffic in the system or due to other circumstances. Activity detectors 36 monitor the RF signals lines 20 to determine which RF signals 20 are active. In the embodiment of FIGURE 2, the activity detectors 36 are signal power sensors. The sensors are commercially available discrete and integrated circuits that incorporate a diode and resistor-capacitor network feeding an operational amplifier. In another embodiment, signal level sensors may be used to detect the activity on an RF signal line 20. The signals generated by the sensors 36 are sent to the logic circuit 48 via an activity detector bus 56. In a typical embodiment, separate connections are provided between each sensor 36A, 36B, etc., and the logic circuit 48. Each of the RF signals 20 is supplied to a unique one of the power dividers 44. Each power divider, in turn, outputs its RF signal to each of the five 1x5 switches 46. For example, power divider 44A supplies RF signal 20A to switches 46A and 46B over lines 50A and 50C, respectively. Power divider 44B supplies RF signal 20B to switches 46 A and 46B over lines 5 OB and 50D, respectively. To reduce the complexity of FIGURE 2, only a few representative connections from the power dividers 44 to the switches 46A are shown. The power dividers illustrated in FIGURE 2 are commercially available from a variety of vendors including, for example, Microwave Associates.

Each switch 46 can be configured to route an RF signal from one of its input lines 50 to its output line 52. The logic 48 controls the configuration of the switches 46 by sending signals sent over a control bus 54. The 1x5 switches 46 illustrated in FIGURE 2 are commercially available from a variety of vendors including, for example, Microwave Associates.

The output of each switch 46 is sensed by a failure detector 38. Typically, the failure detectors 38 are signal power sensors as discussed above. The signals generated by the sensors 38 are sent to the logic circuit 48 via a failure detector bus 58. Again, individual connections typically are provided between each sensor 38 A, 38B, etc., and the logic circuit 48.

Each switch 46 drives one of the antenna subarrays '28 via the lines 52 and 53. Each of the subarrays 28 includes a subarray power divider 60, several medium-power amplifiers 30 and several radiating elements 32.

The subarray power divider 60 distributes the RF signal for the subarray 28 to each medium-power amplifier 30 in the subarray 28. The subarray power divider 60 may be similar to the power divider 44 discussed above.

The medium-power amplifiers 30 in FIGURE 2 illustrate one embodiment where the phase shifters 26 are incorporated within the medium-power amplifiers 30; for example, between gain stages of a given medium-power amplifier 30. When only a single carrier is fed to each subarray, the amplifiers 30 may be single-carrier amplifiers.

Failure detectors 39 sense the output of each amplifier 30. The failure detectors 39 may be signal power sensors similar to those discussed above in conjunction with FIGURE 1. The signals generated by the sensors 39A, 39B, etc., are sent to the logic circuit 48 via a failure detector bus 62. The radiating elements 32 typically consist of printed circuit notches. These printed circuits may be made using conventional micro-strip or strip-line techniques. In one embodiment, the subarrays (e.g., five subarrays) depicted in FIGURE 2 are stacked vertically in the antenna tower. Each subarray is sized according to the desired azimuth and elevation radiation pattern for the site.

Suitable components for the subarray 28 may be obtained from conventional RF component vendors. It is important that the components provide the desired signal characteristics for the signals of interests. Namely, PCS and other wireless bands at frequencies above 800 MHz. For example, the amplifiers 30 may be constructed from monolithic microwave integrated circuits ("MMICs"), bipolar transistor circuits or metal-oxide semiconductor field-effect transistor circuits. Appropriate MMICs may be sold, for example, by Raytheon and Honeywell. The phase shifters 26 typically consist of MMICs and may be sold by the vendors mentioned above. The switch and phase shifter logic 48 configures the switches 46 to distribute the RF inputs among the five subarrays 28. As an example, when only one RF input 20 is to be transmitted, that RF input 20 may be fed to all of the subarrays 28. When two RF inputs 20 are to be transmitted, one RF input 20 may be fed to one half of the subarrays 28 and the other RF input 20 fed to the other half of the subarrays 28. If more RF inputs 20 are to be transmitted, the array is again partitioned.

The switch and phase shifter logic 48 also may send phase shift setting information to the phase shifters (via phase shift bus 64) to control the RF radiation pattern. In the examples in the previous paragraph, the logic 48 would configure the phase shifters 26 in each case to shape the radiation patterns for the desired coverage sector. Various techniques may be used for setting the radiation patterns for an antenna array according to the RF signal distribution and phase settings. FIGURES 3A and 3B illustrate two extreme cases of switch activity. In these examples, the system has five RF inputs, five active antenna subarrays, each of which has four medium power amplifiers and antenna elements. In addition, the elevation and azimuth coverage sectors are specified as ± 10° and 120°, respectively, and the antenna element spacing is 3.62 inches.

In the first case, only one of the RF signals, RF signal 20B, is active. Thus, only activity detector 36B, connected to the active line 20B, will sense an active RF signal. In response to this condition, the switch and phase shifter logic 48 configures all of the switches 46 so they will route the active RF signal 20B to their respective outputs. The logic 48 also sets the first seven phase shifters 26 at each end of the array to 225°, 180°, 90°, 90°, 90°, 45° and 45°. FIGURE 3A depicts an illustrative radiation pattern for this case where the RF signal has a carrier frequency of 1.9575 GHz.

As FIGURE 3A shows, this pattern conforms to the desired elevation coverage. The vertical axis of the plot illustrates the computed EIRP at zero degrees azimuth, assuming each medium-power amplifier generates six watts of power. The desired azimuth coverage is that of the embedded element and is not dependent upon the phase shifter setting.

In the second case, all five RF signals 20 are equally active at separate carrier center frequencies of 1.9571, 1.9573, 1.9575, 1.9577 and 1.9579 GHz, respectively. Thus, the switch and phase shifter logic 48 detects equal activity on each of the RF signal lines 20. Accordingly, the logic 48 configures the switches 46 to distribute each RF signal 20 to a unique subarray 28. The logic 48 also sets all the phase shifters 26 to zero degrees. FIGURE 3B depicts an illustrative elevation pattern and EIRP at zero degrees azimuth for the RF carrier at 1.9575 GHz in this case. Again, the system S provides the desired elevation coverage. The EIRP has dropped by seven dB as a result of diverting power to the other RF carriers. This compares favorably to similar conventional schemes where the EIRP per RF carrier may drop by as much as fourteen dB under these conditions.

By monitoring the power at the outputs of the switches 46 and the medium-power amplifiers 30, the system S may partially compensate for failures in individual power supplies and switches. Specifically, the logic 48 may cause the switches 46 to reroute the RF signals 20 to other subarrays 28 and may adjust the phase shifters 26, as appropriate. These adjustments may be made based on a priori settings stored in the logic 48 or in a data memory or by other means. To reconfigure the antenna array, the logic circuit 48 performs several sensing and control operations. For example, to adapt to the activity of the incoming RF signals 20, the logic 48 may sense the signals on the activity bus 56 to determine how many RF signals 20 are active. A priori switch settings 66 may specify which subarrays 28 are to receive an RF signal for the cases of one, two or three, etc., active RF signals 20. The logic 48 would then send signals over the bus 54 to configure the switches 46 as specified.

Similarly, a priori phase settings 68 may specify the phase shifts to be used according to the number of RF signals 20 that are active and according to which subarrays 28 are being used to transmit the RF signals 20. For example, the settings 68 may have a map that specifies the phase for each phase shifter 26 for each possible combination of active RF signals 20 and operating subarrays 28. Thus, there may be one list of settings used when there is one active RF signal 20 and five operating subarrays 28, there may be another list used when there are two active RF signals 20 and four operating subarrays 28, and so forth. As above, the logic 48 sends signals over the bus 64 to configure the phase shifters 26, as necessary.

Similar procedures may be used to compensate for component failures. The logic 48 may sense the signals on the buses 58 and 62 to determine which components have failed. The a priori settings may specify how the switches 46 and phase shifters 26 are to be configured in response to different permutations of components failures.

The format of the control signals provided over the buses 54 and 64 depends on the characteristics of the switches 46 and the phase shifters 26. For example, analog switches and phase shifters may be integrated with digital control logic. In this case, the logic 48 would send digital signals to specify the switch and phase settings.

The speed with which the detectors 36, 38 and 39, the logic 48, the switches 46 and the phase shifters 26 operate to change the switch and phase shifter settings depends on the requirements of the specific implementation of the system. In most cases, relatively modest switching and setting speeds will keep up with changes in input RF signal loads without causing noticeable call drop-outs.

It would be apparent to one skilled in the art, given the teachings herein, that a variety of structures may be used to control the switch and phase settings. For example, various digital and/or analog circuits may be used. In addition, the a priori settings may define algorithms rather than simple maps.

The network preceding the amplifier 30 (e.g., the power dividers 44 and 60, the switches 46 and the phase shifters 26) may be implemented, in part, with analog or digital circuitry. FIGURE 2 discussed above illustrates one embodiment of an analog implementation. FIGURE 4 illustrates one embodiment of a digital implementation that provides digital signals to several active antenna subarrays 70 (subarray 1 through subarray N).

The flowchart of FIGURE 5 describes typical operations performed by the system of FIGURE 4. Initially, the system S (FIGURE 4) is configured according to default phase and switch settings stored in data memory 71 (see FIGURE 6). The default switch settings are retrieved (block 202) and used to configure the digitally implemented switching network (block 204). The default phase settings are retrieved (block 206) and used to configure the digitally implemented phase shifters (block 208). Implementations of the digital switching network and phase shifters are discussed below. Beginning at block 210, the system S processes each of the active RF signals that are received via RF input lines 73. Initially, the RF signals are converted to digital signals. For example, down-converters 72 (e.g., channel mixers) may frequency shift each of the RF signals to baseband signals to remove the RF carrier component of the signal (block 212). As described below in conjunction with FIGURE 7, the down-converters 72 may instead frequency shift the RF signals to an intermediate frequency range that is desired for the analog-to-digital conversion process (block 212).

A local oscillator distribution network provides the reference frequency for the down- converters 72 and up-converters in the subarrays 70 (discussed below). The local oscillator distribution network includes a local oscillator 82 and several power dividers 84 A and 84B. The down-converted signals are fed to filters 79. The filters 79 remove spurious signals that may result from the down-conversion (e.g., mixing) operation.

At block 214, analog-to-digital converters 74 convert the filtered, down-converted signals for each RF signal to digital RF signals. The digital RF signals comprise digital data that represents the analog RF information. In some implementations, baseband or digital call signals may be directly available from other components in the transmission system. In this case, the down-converters 72 or the analog-to-digital converters 74 and related components may be omitted.

The digital RF signals associated with each input RF signal are sent via data bus 77 to a digital signal processor 76 (or several digital signal processors operating in parallel). As represented by block 216 in FIGURE 5, the digital signal processor 76 processes the digital RF signals to control the phase shift of the RF signals. In addition, the digital signal processor 76 may perform a switching function to distribute the digital RF signals to the appropriate subarrays 70 (block 218). Additional details regarding the operation of one embodiment of a digital signal processor are described below in conjunction with FIGURE 7.

The RF power modules 78 in the subarrays 70 up-convert, amplify, and recombine the digital signals to provide the desired array illumination. FIGURE 6 illustrates one embodiment of an RF power module 78. In FIGURE 6, the digital signal processor 76 provides quadrature (I and Q) baseband signals and phase signals for each channel. To reduce the complexity of

FIGURE 6, only one channel is shown. Digital-to-analog converters 93 convert the digital I and Q signals to analog signals (block 220, FIGURE 5). At block 222, an RF up-converter 94 frequency shifts the baseband analog signals using, as a reference, the local oscillator signal that was used in the down-conversion process. The signals are thus restored to their original carrier frequency. At block 224, the up-converted signal is routed to an amplifier and filter 95. After the signals are amplified and undesired signals removed by filtering, the RF signals passes to a 3-dB hybrid 105, which is coupled to a termination 96 and a directional coupler 98. At block 226, the up-converted signal is sent to a radiating element 32 (FIGURE 4) via RF OUT.

Calibration and other feedback may be provided in the RF power module 78, for example from directional coupler 98 via the RF SAMPLE TO CALIBRATE/BIT SWITCH line 97. A sample of the RF output may be provided to a calibration/BIT switch 75 (FIGURE 4). The sample may then be used to provide corrections to the digital baseband signal to improve signal fidelity. Various techniques are known in the art for this purpose. The sample also may provide component failure information that is sent back to the digital signal processor 76 or some other switch and phase control component.

FIGURE 7 illustrates several digital signal processor components/operations for one embodiment of the invention. In this embodiment, the down-converters 72 (FIGURE 4) frequency shift the RF signals to an intermediate frequency range before the analog-to-digital conversion operation. The digital output of the analog-to-digital converter 74 is fed to the input of a digital down-converter 81. The digital down-converter 81 uses a complex frequency translation operation to translate the frequency of the signal by one quarter of the sample rate (i.e., Fs/4) of analog-to-digital converter 74. The digital down-converter 81 also filters the signal to remove the undesired harmonic component at Fs/2. In addition, the output samples are decimated by a factor of two to reduce the sample rate. In sum, the digital down-converter 81 converts sampled real signals into complex baseband signals and decimates the complex baseband signals. The output of the digital down-converter 81 consists of an in-phase (I) component and a quadrature- phase (Q) component. An input equalizer 85 equalizes amplitude and phase variations that may exist in the signal. In one embodiment, the input equalizer 85 is a finite impulse response (FIR) filter. The FIR filter filters the signal based on equalizer filter coefficients generated by an adaptive frequency equalization controller 90. The controller 90 may generate equalizer FIR coefficients (e.g., h, and h₂) from samples of the input and output RF signals (S_in(n) and S_out(n)) using techniques that are well-known in the signal processing art.

A rectangular-to-polar converter 86 converts the rectangular coordinate in-phase (I) and quadrature-phase (Q) input to a polar coordinate amplitude format. The phase component represents the angle modulation component of the input signal. The amplitude component represents the envelope component of the input signal.

The phase component is coupled to the input of a phase shifter 87. Here, the digital signal processor 76 processes the digital RF signals to control the phase shift of the RF signals. For example, as discussed herein, default settings and other data (e.g., stored in data memory 71 ) may be used to manipulate the signal. Also, in response to component failures and changes in incoming signal activity, the digital signal processor 76 may control the phase shift settings and reconfigure the antenna array. In one embodiment, the phase shifter adds or subtracts a delta phase shift to or from the phase data, respectively.

In one embodiment, an adaptive calibration controller 107 provides phase calibration signals (cal. phase) and amplitude calibration signals (cal. amp) for the calibration/BIT switch operations described in conjunction with FIGURE 4. These calibration signals may, for example, be added to the phase and amplitude components of the signal by the phase shifter 87 and the polar-to-rectangular converter 88, respectively. The output of the phase shifter 87 and the amplitude data are sent to a polar-to-rectangular converter 88. The polar-to-rectangular converter 88 converts the polar coordinate amplitude and phase input signals into rectangular in-phase (I) and quadrature-phase (Q) signals.

An equalizer 89 equalizes amplitude and phase variations that may exist in the signals. In one embodiment, the equalizer 89 includes FIR filters that operate based on equalizer coefficients (e.g., h₂) generated by adaptive frequency equalization controller 90.

A digital up-converter 91 interpolates the I and Q baseband signals and converts them to real signals. The resultant signals are routed to the subarrays 70 where they are converted to analog format by digital-to-analog converter 92 and processed in a similar manner as described above in conjunction with FIGURE 6.

As discussed above, the digital signal processor 76 may perform a switching function to distribute the digital RF signals to the subarrays 70. That is, the digital signal processor 76 may be used to route the digital RF signals associated with a given input RF signal (as modified with the appropriate phase settings) to the RF power modules 78 in a designated subarray 70. The switching function may be accomplished using digital signal processors that can process multiple input and output data streams and/or using several digital signal processors. For example, in the embodiment of FIGURE 4 the digital signal processor 76 has several input ports and output ports.

Each input port may be mapped to a given RF signal input line 73. Each output port may be mapped to a given active antenna subarray 70. To perform the switching function, the digital signal processor 76 routes data received via an input port to the appropriate output port so that the RF signal will be routed over data bus 80 to the desired active antenna subarray 70. When several digital signal processors are used, data multiplexers (not shown) may be used to route data from an RF signal source to a particular digital signal processor. Similarly, data multiplexers may be used to route data from a digital signal processor to a particular active antenna subarray 70.The digital signal processor 76 may be programmed to provide the activity detector operations discussed herein. For example, signal analysis algorithms (represented by activity detector 83 in FIGURE 7) may be employed to calculate signal activity based on the modulation rate of the signal.

The digital feed network implementation described in FIGURES 4 through 7 provides several advantages. For example, reconfiguration of the array may be accomplished digitally. This may provide a lower cost system and a more flexible method of reconfiguring the array in comparison to an analog network. In addition, the digital RF modules may be transformed to optimize RF module performance.

In general, commercial off-the-shelf down-converters, analog to digital converters, digital to analog converters and local oscillators may be used to implement the embodiment of FIGURES 4 through 7. The power dividers, antenna elements, amplifiers and other components may be similar to those discussed above in conjunction with FIGURE 2.

The operations described above may be implemented in a variety of ways. For example, the digital signal processing operations may be implemented in a commercially available digital signal processor. These may also be implemented using a conventional microprocessor (e.g., a PENTIUM^® processor sold by INTEL^®) and appropriate signal processing software. Many of these functions also may be implemented using off-the-shelf or custom integrated circuits. In a similar manner, the signal analysis, signal routing, phase shifting and calibration operations may be implemented using various combinations of hardware and software. Also, although the embodiment of FIGURE 7 performs many of the digital processing operations in the polar coordinate domain, the processing could be performed in the I and Q domain.

Referring now to FIGURE 8, one embodiment for implementing the array reconfiguration operations discussed above is treated in detail. A switch and phase control circuit 99 (center) updates switch settings 101 and phase settings 103 (right) using call analysis techniques and using settings and procedures that may be modified to adapt to new site requirements. FIGURE 9 describes operations that may be performed by the embodiment of FIGURE

8. Beginning at block 250, site requirements 100 such as configuration defaults and adjustment procedures are stored in a data memory 102. At block 252 and 254, the system receives default settings for the switch configuration and the phase shifters and stores them as default switch settings 104 and default phase settings 106.

At block 256 and 258, the system receives adjustment procedures to be implemented in response to component failures and changes in the incoming RF signal traffic. Logical expressions of these procedures are stored as traffic adjustment procedures 108 and failure adjustment procedures 110. These procedures are discussed in more detail below.

Blocks 260 through 264 illustrate an alternative implementation where the system automatically determines the switch and phase shifter settings without relying on a priori settings. For example, these settings may be calculated based on a desired radiation pattern for the site. At block 260, the system receives and stores radiation pattern specifications 112. Typical specifications may include azimuth and elevation parameters.

At block 262, a call analysis operation 114 in the system analyzes the incoming call traffic to, for example, determine how many incoming RF signals 20 are active. In one embodiment, the system tracks traffic based on the strength of the incoming RF signals. In another embodiment, the system tracks traffic based on the signal-to-noise ratio of the incoming signals. At block 264, the switch and phase control 99 uses the information from blocks 260 and

262 to calculate the switch and phase settings that will provide the desired array illumination. For example, table look-ups or algorithms may be used to calculate these settings.

At block 266, the switch and phase control 99 sets the initial values of the switch settings 101 and the phase settings 103. That is, the switch and phase control 99 sets up the configurations of the switch (e.g., switches 46 in FIGURE 2 or the switch configuration in the digital signal processor 76 in FIGURE 4) and configures the phase shifters (e.g., shifters 26 or 87).

At block 268, the system monitors and waits for changes that affect the switch and phase settings. If the change simply involves new defaults for the switch or phase settings, the process proceeds to block 266 where the switch and phase control 99 updates the settings, as necessary.

If the change involves new specifications (e.g., a new radiation pattern for one or more of the RF signals broadcast by the site), the process proceeds to block 260 and the switch and phase control 99 performs the above-described operations to update the switch and phase settings, as required. If at block 268 the call analysis operation 114 sensed a change in the call traffic, an indication of the change is provided to a traffic compensator 116 via a line 118. At block 270, the traffic compensator 116 uses the traffic information and the traffic adjustment procedures 108 to calculate new switch and phase settings. Typically, the traffic adjustment procedures 108 will involve a table look-up operation that maps the number of active RF signals with a predefined subarray allocation for each RF signal. However, other more sophisticated algorithms may be used. For example, to reduce interference for a channel associated with a specific RF signal, different broadcast signal strengths and radiation patterns may be specified for that channel. Thus, the traffic compensator 116 may use the radiation pattern information discussed above to generate the new settings.

If at block 268 one or more failure detectors 38 sensed a component failure, the failure detectors 38 provide an indication of the failed component to a failure compensator 120 via a line

122. At block 272, the failure compensator 120 uses the failure information and the failure adjustment procedures 110 to calculate new switch and phase settings. In a manner related to the operations discussed above for block 270, the failure adjustment procedures 110 may define simple table look-up operations or more sophisticated algorithms.

Many of the operations described above for FIGURES 8 and 9 may be implemented using various combinations of hardware and software. In a hardware implementation, the operations may be accomplished, for example, using off-the-shelf or custom integrated circuits. In addition, conventional random access memories may be used to store the dynamic information (e.g., the defaults). In a software implementation, the operations may be accomplished, for example, using programs executed by a microprocessor.

A typical application of the reconfigurable active phased array discussed above is as a final amplifier and antenna for wireless communication base stations including PCS and other wireless bands at frequencies above 800 MHz. FIGURE 10 illustrates a high-level view of a communications system C that provides includes cellular and PCS systems.

Inbound call traffic for a cell site 124 and a PCS site 126 (center) may consist of various communications media and may originate from a variety of transmission systems. For example, the call traffic may originate from telephones 132 (upper right), facsimile machines 134, computers 136 or a number of other communication devices (not shown). The call traffic may be routed through a network such as a PSTN 128 or an Internet 130.

Interfaces 132 in a cellular base station 138 and a PCS base station 140 send the call traffic to transmitters 134 and receive call traffic from receivers 136. The transmitters 134 and receivers 136 send and receive RF signals to and from the active antenna subarrays 28 as discussed above. The active antennas broadcast and receive RF waves 144 to and from cellular telephones 146, PCS equipment 148 and other equipment (not shown).

In a typical implementation, the active antenna array (comprised of the subarrays 28) is placed on the antenna support tower (not shown). The remaining components (e.g., the switching network 24 in FIGURE 2 or the digital signal processor 76 in FIGURE 4) are placed in the base station located near the tower. It will be apparent that the cables 142 to the active antenna subarrays 28 may carry lower power signals in comparison to cables in many conventional systems.

A system constructed according to the invention described above may provide a number of improvements over conventional systems. The system may not need expensive low-loss cable runs from the final amplifier to the antenna. The system may use multiple medium power amplifiers instead of high power amplifiers. As a result, the system may be subjected to less high-power related component stress. In addition, the redundancy provided by the use of multiple amplifiers improves the reliability of the overall system. Furthermore, the switching network allows full power use of all of the antenna subarrays when one or more RF carriers are being transmitted. In contrast, conventional final amplifiers typically must reduce power to transmit multiple carriers. The phase shifters allow dynamic shaping of the antenna radiation pattern. This reduces the losses when multiple RF carriers are used and allows the radiation pattern to be tailored to specific antenna site location requirements. Moreover, the invention may provide automatic reconfiguration of the allocation of the RF carriers to the subarrays to compensate for component failures. These features are particularly beneficial where the cell sites have different or dynamic pattern requirements. For example, there may be interference problems between cell sites that can be resolved by changing the radiation pattern. These problem exists because the same frequency or code modulation may be reused from one cell to the next. Thus, there may be interference between some calls handled by the adjacent sites because the radiation patterns for adjacent cell sites may overlap to some extent. The effects of this problem may be diminished by adjusting the pattern for one or more of the sites. The present invention effectively provides this capability.

While certain specific embodiments of the invention are disclosed as typical, the invention is not limited to these particular forms, but rather is applicable broadly to all such variations as fall within the scope of the appended claims. To those skilled in the art to which the invention pertains many modifications and adaptations will occur. For example, various methods of signal distribution may be used in practicing the invention. A variety of methods may be used for accomplishing phase shifting. A number of traffic analysis and failure detection methods may be used to determine when to reconfigure the array. Thus, the specific structures and methods discussed in detail above are merely illustrative of a few specific embodiments of the invention.

Claims

WHAT IS CLAIMED IS:

1. A method for reconfiguring the distribution of radio frequency signals to a plurality of active antennas, said method comprising the steps of: distributing a plurality of radio frequency signals to a plurality of subarrays; receiving an indication to change said distribution of said radio frequency signals to said subarrays; and reconfiguring said distribution of said radio frequency signals in response to said indication.

2. A method according to claim 1 further comprising the step of sensing at least one of said radio frequency signals to generate said indication.

3. A method according to claim 1 further comprising the step of sensing incoming channel traffic associated with at least one of said radio frequency signals to generate said indication.

4. A method according to claim 1 further comprising the step of sensing a component failure to generate said indication.

5. A method according to claim 4 wherein said sensing step further comprises the step of sensing output signals associated with said radio frequency signals.

6. A method according to claim 1 wherein said reconfiguring step further comprises the step of shifting a phase of at least one of said radio frequency signals.

7. A method according to claim 6 wherein said shifting step alters a radiation pattern associated with at least one of said subarrays.

8. A method according to claim 6 wherein one of said signals are distributed to a plurality of subarrays, said shifting step further comprising the step of individually setting said phase for each of said radiating elements.

9. A method according to claim 1 wherein said reconfiguring step further comprises the step of using at least one a priori setting.

10. A method according to claim 1 wherein said reconfiguring step further comprises the step of using at least one a priori setting to control distribution of at least one of said radio frequency signals to at least one of said subarrays.

11. A method according to claim 1 wherein said reconfiguring step further comprises the step of using at least one a priori setting to control a phase angle of at least one of said radio frequency signals.

12. An active antenna system for distributing radio frequency signals, said system comprising: a switching network for distributing a plurality of radio frequency signals to a plurality of subarrays; a plurality of subarrays for producing radio frequency waves from said radio frequency signals; and an array configuration controller, responsive to an indication to change said distribution of said radio frequency signals to said subarrays, for cooperating with said switching network to reconfigure said distribution of said radio frequency signals.

13. An active antenna system according to claim 12 further comprising at least one signal detector for sensing at least one of said radio frequency signals.

14. An active antenna system according to claim 12 further comprising at least one activity detector for sensing incoming channel traffic associated with at least one of said radio frequency signals.

15. An active antenna system according to claim 12 further comprising at least one power sensor for sensing a power level associated with at least one of said signals.

16. An active antenna system according to claim 12 wherein said active antenna elements include a single carrier power amplifier and a phase shifter.

17. An active antenna system according to claim 12 further comprising a data memory for storing at least one a priori signal distribution setting for said switching network.

18. An active antenna system according to claim 12 further comprising at least one phase shifter for altering a phase of at least one of said radio frequency signals.

19. An active antenna system according to claim 18 further including a phase shift controller, responsive to an indication to change said distribution of said radio frequency signals to said subarrays, for cooperating with said at least one phase shifter to alter said phase.

20. An active antenna system according to claim 12 further comprising a data memory for storing at least one a priori phase shift setting for said at least one phase shifter.

21. An active antenna system according to claim 12 wherein said switching network comprises: at least one power divider for distributing incoming signals associated with said radio frequency signals to at least one switch; and at least one switch, configurable to distribute each of said incoming signals to at least one of said subarrays .

22. An active antenna system according to claim 12 further comprising means for detecting a failure of a component in said system.

23. An active antenna system according to claim 12 wherein said active antennas comprise a plurality of subarrays wherein each of said subarrays comprises a plurality of active antenna elements and each of said subarrays is individually connected to said switching network.

24. An active antenna system according to claim 23 wherein each of said active antenna elements further comprises an individually controllable phase shifter.

25. A system for distributing radio frequency signals to a plurality of subarrays, said system comprising: a switching network for distributing a plurality of radio frequency signals to said plurality of subarrays; means for initiating a change in said distribution of said radio frequency signals to said subarrays; and an array configuration controller, responsive to said means, for cooperating with said switching network to reconfigure said distribution of said radio frequency signals.

26. A cellular communications system for transmitting a plurality of cellular calls, said system comprising: a switching network for distributing a plurality of radio frequency signals associated with said cellular calls to a plurality of active antenna elements; a plurality of active antenna elements for producing radio frequency waves from said radio frequency signals, said modules comprising at least one phase shifter, at least one single carrier amplifier and at least one radiating element; and an array configuration controller, responsive to an indication to change said distribution of said radio frequency signals to said active antenna elements, for cooperating with said switching network to reconfigure said distribution of said radio frequency signals.

27. A system for distributing radio frequency signals to a plurality of antennas, said system comprising: an analog to digital converter for generating digital signals according to said radio frequency signals; a digital signal processor for distributing said digital signals to a plurality of power modules; and a plurality of power modules for converting said digital signals to analog signals and providing said analog signals to said plurality of antennas.

28. A system according to claim 27, further comprising a local oscillator for supplying a reference signal to said power modules and a down-converter.

29. A method for distributing radio frequency signals to a plurality of antennas, said method comprising the steps of: converting said radio frequency signals to digital signals; distributing said digital signals to a plurality of power modules converting said digital signals to analog signals; and supplying said analog signals to said antennas.

30. A method according to claim 29, further comprising the steps of: receiving an indication to change said distribution of said digital signals to said power modules; and reconfiguring said distribution of said digital signals in response to said indication.

31. A method according to claim 30, further comprising the step of shifting a phase of said digital signal in response to said indication.