Patent Publication Number: US-8971796-B2

Title: Repeaters for wireless communication systems

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of and claims the benefit of U.S. Ser. No. 13/745,540, filed Jan. 18, 2013, entitled “REPEATERS FOR WIRELESS COMMUNICATION SYSTEMS”; which application is a continuation application of and claims the benefit of U.S. Ser. No. 13/220,541, filed Aug. 29, 2011, entitled “REPEATERS FOR WIRELESS COMMUNICATION SYSTEMS”, now issued U.S. Pat. No. 8,358,970, issued Jan. 22, 2013; which patent is a continuation application of and claims the benefit of U.S. Ser. No. 12/538,508, filed Aug. 10, 2009, entitled “REPEATERS FOR WIRELESS COMMUNICATION SYSTEMS”, now Issued U.S. Pat. No. 8,010,042, issued Aug. 30, 2011; which patent is a continuation application of and claims the benefit of U.S. Ser. No. 10/181,109, filed Sep. 10, 2003, entitled “REPEATERS FOR WIRELESS COMMUNICATION SYSTEMS”, now issued U.S. Pat. No. 7,577,398, issued Aug. 18, 2009; which patent is the U.S. National Phase of PCT Application No. PCT/US01/01446, filed Jan. 16, 2001, entitled “REPEATERS FOR WIRELESS COMMUNICATION SYSTEMS”; which application is a PCT Application, which claims the benefit of the following applications: 
     U.S. Provisional Ser. No. 60/245,010, filed Nov. 1, 2000; 
     U.S. Ser. No. 09/694,225, filed Oct. 23, 2000, now issued U.S. Pat. No. 6,934,511, issued Aug. 23, 2005, which patent is a continuation-in-part application of and claims the benefit of the following applications: U.S. Ser. No. 09/483,234, filed Jan. 14, 2000, now issued U.S. Pat. No. 6,745,003, issued Jun. 1, 2004; U.S. Ser. No. 09/357,032, filed Jul. 20, 1999, now issued U.S. Pat. No. 6,731,904, issued May 4, 2004; U.S. Ser. No. 09/483,649, filed Jan. 14, 2000, now abandoned. 
     U.S. Ser. No. 09/687,862, filed Oct. 13, 2000, now abandoned, which application is a continuation-in-part application of and claims the benefit of U.S. Ser. No. 09/483,649, filed Jan. 14, 2000, now abandoned; 
     U.S. Ser. No. 09/513,543, filed Feb. 25, 2000, now issued U.S. Pat. No. 7,068,973, issued Jun. 27, 2006; 
     U.S. Ser. No. 09/506,245, filed Feb. 17, 2000, now issued U.S. Pat. No. 6,445,904, issued Sep. 3, 2002; 
     U.S. Ser. No. 09/483,649, filed Jan. 14, 2000, now abandoned; 
     U.S. Ser. No. 09/483,234, filed Jan. 14, 2000, now issued U.S. Pat. No. 6,745,003, issued Jun. 1, 2004, which patent is a continuation-in-part application of and claims the benefit of U.S. Ser. No. 09/357,032, filed Jul. 20, 1999, now issued U.S. Pat. No. 6,731,904, issued May 4, 2004; 
     the applications and patents being incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to repeaters for use in wireless communication systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a flat-panel repeater system having a housing having a pair of oppositely facing surfaces, at least one antenna element mounted to each of the surfaces for radiating energy in a direction opposite to that of an antenna element mounted to the other of the surfaces, and an electronic circuit mounted within the housing and operatively coupling signals between at least one antenna element on each of the oppositely facing surfaces of the module. 
     One preferred embodiment of the invention improves isolation between the antennas on opposite sides of the flat-panel repeater by use of adaptive cancellation which removes a significant portion (between 10 dB and 40 dB) of the feedback signal power, therefore increasing the total system isolation by the same amount (10 to 40 dB). This additional isolation can be used to achieve greater system gain, and therefore significantly extend the range of the system. The cancellation scheme uses digitally processed information to generate a signal, which, when added to the original input signal, cancels the feedback signal. This is especially useful in a side-side repeater. 
     In one particular embodiment of the invention having a base-station-facing antenna mounted on one of the opposing sides of the housing and a mobile-facing antenna mounted on the other of the opposing sides of the housing, the two antennas each comprise an array of antenna elements, and a beamforming arrangement creates a desired antenna pattern of the base-station-facing antenna relative to a base station and a desired antenna pattern of the mobile-facing antenna relative to subscriber equipment. 
     In a further aspect of the invention, the problem of equal gain combining with a mobile signal source is overcome by the use of polarization diversity in a repeater. The vertical and horizontal field components in a communications link are highly uncorrelated, and thus by using receive antennas that have the same phase center and orthogonal polarizations, the problem of location-induced phase variation is eliminated. Therefore, an equal gain combiner can be utilized that has a fixed phase adjustment dependent only on the fixed phase differences of the repeater equipment, and not upon the changing location of the mobile signal source. 
     The invention provides a repeater diversity system comprising a main null antenna having a given phase center and polarization for receiving a communications signal from a remote signal source, a donor antenna for transmitting a signal to a base station, a diversity null antenna having the same phase center as the main null antenna and a polarization orthogonal to the polarization of the main null antenna, a combining network coupled to the main null antenna and the diversity null antenna for combining the signals therefrom, and an uplink channel module coupled with the combining network for delivering diversity combined receive signals to the donor antenna. 
     Another aspect of the invention uses simple RF electronics, and Butler matrix technology, to provide a mechanism to electronically steer an antenna beam toward the direction of the base station. A planar antenna, which may have a multiplicity of antenna elements, is used to generate a plurality of RF beams, via the RF Butler matrix. Each beam is presented to an RF switch. The controlled switch toggles each beam, and the best beam is selected for RF input/output port(s). Additionally, the use of this antenna results in a narrow beam that reduces view to interfering signals and therefore increases the carrier-to-interference (C/I) ratio of the system. 
     The invention provides a radio frequency switched beam planar antenna system comprising a support structure, a plurality of antenna elements mounted to the support structure, a Butler matrix mounted to the support member, the Butler matrix having a plurality of inputs coupled respectively with the antenna elements and a plurality of outputs, and a radio frequency switching circuit mounted to the support structure and operatively coupled with the outputs of the Butler matrix and having a control port responsive to a control signal for causing the switching circuit to select one of the outputs of the Butler matrix at a time. 
     The present invention also provides a system for re-transmitting a GPS signal or other received satellite signals inside a structure. The system receives the satellite signal, amplifies the received signal to produce a second satellite signal, and re-transmits the second signal inside the structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. 
         FIG. 1  is a perspective view of a flat-panel repeater embodying the invention; 
         FIG. 2  is an exploded perspective view of the repeater of  FIG. 1 ; 
         FIG. 3  is a perspective view of another flat-panel repeater embodying the invention; 
         FIG. 4  is an exploded view of the repeater of  FIG. 3 ; 
         FIG. 5  is a schematic representation of a repeater module in accordance with one embodiment of the invention; 
         FIG. 6  is a schematic representation of another form of repeater module in accordance with another embodiment of the invention; 
         FIG. 7  is an enlarged end elevation of one of the RF choke frames in the repeater of  FIGS. 3 and 4 ; 
         FIG. 8  and  FIG. 9  are a perspective view and a partial side sectional view of another embodiment of an RF choke structure for a flat-panel repeater; 
         FIG. 10  and  FIG. 11  are a perspective view and a partial side sectional view of another embodiment of an RF choke structure for a flat-panel repeater; 
         FIG. 12  and  FIG. 13  are a perspective view and a partial side sectional view of another embodiment of an RF choke structure for a flat-panel repeater; 
         FIG. 14  and  FIG. 15  are side sectional and top views, respectively, of a reduced surface wave (RSW) patch antenna; 
         FIG. 16  is a simplified perspective illustration of one form of flat-panel repeater in accordance with one form of the invention; 
         FIG. 17  is a simplified illustration of a second form of flat-panel repeater in accordance with the invention; 
         FIG. 18  is a simplified perspective illustration showing another embodiment of a flat-panel repeater; 
         FIG. 19  is a diagrammatic representation of an in-building repeater system in accordance with the invention; 
         FIGS. 20 and 21  are simplified illustrations of repeater modules in accordance with other forms of the invention; 
         FIG. 22  is a diagrammatic representation of another form of in-building repeater system in accordance with the invention; 
         FIG. 23   a  is a diagrammatic illustration of a system for distributing signals from multiple wireless services throughout a building; 
         FIG. 23   b  is a diagrammatic illustration of a PCS converter used in the system of  FIG. 23   a;    
         FIG. 24  is a block diagram of one signal path through a repeater system; 
         FIG. 25  is a block diagram of one signal path through a repeater system, as in  FIG. 24 , adding an adaptive cancellation circuit; 
         FIG. 26  is a block diagram (high level) of a (digitally) adaptive cancellation circuit in accordance with one embodiment of the invention; 
         FIG. 27  is a block diagram (high level) of the (digitally) adaptive cancellation circuit of  FIG. 26  which shows the technique in further detail; 
         FIG. 28  is a block diagram of a repeater system, similar to that of  FIG. 17 , using the adaptive cancellation (AC) circuit of  FIGS. 26 and 27 ; 
         FIGS. 29 and 30  show the directional characteristics of the AC blocks, for the downlink path ( FIG. 29 ) and the uplink path ( FIG. 30 ); 
         FIGS. 31 and 33  show two examples of side-to-side repeaters; 
         FIGS. 32 and 34  show block diagrams of the side-to-side repeater systems of  FIGS. 31 and 33 , respectively, with the addition of adaptive cancellation; 
         FIG. 35  is a simplified view of a repeater system of the prior art; 
         FIG. 36  is a simplified view, in a form similar to  FIG. 35 , showing a repeater in accordance with one embodiment of the invention; 
         FIG. 37  is a diagrammatic illustration of beam steering in an integrated repeater system of the invention; 
         FIG. 38  is a block schematic diagram of one form of a repeater in accordance with the invention, utilizing a duplexed antenna; 
         FIG. 39  is a block schematic similar to  FIG. 38  but illustrating implementation with separate transmit and receive antennas; 
         FIG. 40  is a simplified illustration of a patch antenna array; 
         FIG. 41  is a simplified representation, in a form similar to  FIG. 40 , of a dipole antenna array; 
         FIGS. 42 and 43  are flowcharts or flow diagrams of a repeater setup program in accordance with one embodiment of the invention; 
         FIG. 44  is a flowchart or flow diagram of one embodiment of a repeater main operation loop; 
         FIG. 45  is a functional diagram showing beamsteering via a Butler matrix; 
         FIG. 46  is a simplified schematic diagram showing beamsteering using phase shifters; 
         FIG. 47  is a perspective view of a flat-panel repeater design; 
         FIG. 48  is a perspective view illustrating a beamsteering scheme via tilting of flat panel arrays similar to the flat panel array of  FIG. 47 ; 
         FIG. 49  and  FIG. 50  are two diagrammatic representations of beamsteering using striplines of different lengths; 
         FIG. 51  is a perspective view of a solar-powered battery for a repeater; 
         FIG. 52  is a diagrammatic illustration of a modified in-building repeater system using physically separated antennas; 
         FIGS. 53-53   g  are diagrammatic illustrations of modified repeaters using physically separated antennas; 
         FIG. 54  is a diagrammatic illustration of another modified repeater using physically separated antennas; 
         FIG. 55  is a functional block diagram of a single repeater cell of a side-to-side repeater for a TDD communication system in accordance with one form of the invention; 
         FIG. 56  shows in diagrammatic form multiple cells having the general configuration shown in  FIG. 55 ; 
         FIG. 57  is a somewhat diagrammatic view showing a repeater in accordance with one form of the invention; 
         FIG. 58  is a simplified elevation showing a repeater tower structure in accordance with one embodiment of the invention; 
         FIG. 59  is a circuit schematic illustrating a diversity repeater system in accordance with one embodiment of the invention; 
         FIG. 60  is a circuit schematic illustrating a diversity repeater system in accordance with a second embodiment of the invention; 
         FIG. 61  is a simplified showing of two antennas having the same phase center and mutually orthogonal polarizations; 
         FIG. 62  is a block diagram showing a plurality of antenna elements coupled to an RF Butler matrix; 
         FIG. 63  shows an example of a beam pattern for one of the spatial (antenna) elements of  FIG. 62 ; 
         FIG. 64  shows a system, similar to  FIG. 62  using four antennas; 
         FIG. 65  shows an approximate azimuth beamwidth response for the Butler matrix in  FIG. 64 ; 
         FIG. 66  is a plan view, somewhat diagrammatic in form, of a planar switched beam antenna system; 
         FIG. 67  is a simplified top view of one of the patch antenna elements of the system of  FIG. 66 ; 
         FIG. 68  is a simplified diagram of an RF switch of the system of  FIG. 66 ; 
         FIG. 69  is a block diagram of the circuit of  FIG. 66 ; 
         FIG. 70  is a block diagram similar to  FIG. 69  with an RF to IF transceiver (transverter) added; 
         FIG. 71  is a block diagram similar to  FIG. 70  with a modem added; 
         FIG. 72  is a simplified perspective view of a planar system (unit), indicating the elements of  FIG. 71 ; 
         FIG. 73  is a view, similar in form to  FIG. 66 , showing an embodiment having separate transmit and receive antenna elements; 
         FIG. 74  is a block diagram of the circuit of  FIG. 73 ; 
         FIG. 75  shows the circuit of  FIG. 74 , adding an RF to IF downconverter (or receiver) for the receive mode, and IF to RF upconverter (or transmitter/exciter) for the transmit mode; 
         FIG. 76  shows the circuit of  FIG. 75 , adding a modem; 
         FIG. 77  shows a system similar to  FIG. 66 , using elevation arrays in place of single array elements; 
         FIG. 78  is a simplified view in a form similar to  FIG. 720 , showing 360 degree coverage, employing two such systems, back to back, to generate, in effect, an omni-directional system; 
         FIG. 79  shows an alternative structure for obtaining 360 degree coverage, using dipole antenna elements on a PCB; 
         FIG. 80  shows approximate azimuth beams for the system of  FIG. 79 ; 
         FIG. 81  is a simplified perspective view showing an indoor installation of a system in accordance with the invention; 
         FIG. 82  is a perspective view of a flat panel antenna for a laptop or similar portable computer; and 
         FIG. 83  is a perspective view showing a laptop computer with the flat panel antenna of  FIG. 82 . 
         FIG. 84  is a diagrammatic top plan view of a repeater having multiple mobile-facing antennas to provide wider angle coverage; 
         FIG. 85  is a schematic diagram of an electronic system for use in the repeater of  FIG. 84 ; 
         FIG. 86  is a diagrammatic top plan view of a repeater having a modified mobile-facing antenna for providing wide-angle coverage; 
         FIG. 87  is a diagrammatic top plan view of a repeater having another modified mobile-facing antenna for providing wide-angle coverage; 
         FIG. 88  is a diagrammatic top plan view of a repeater having a mobile-facing base-station-facing antennas in planes that are not parallel to each other; 
         FIG. 89  is a diagrammatic side elevation of a building containing a repeater for re-transmitting signals in a direction orthogonal to the direction in which the signals are received; 
         FIG. 90  is a structure that includes a GPS repeater system according to one embodiment of the invention; 
         FIG. 91  is another structure that includes a GPS repeater system according to another embodiment of the invention; 
         FIG. 92  is a block diagram of a primary GPS repeater used in the GPS repeater systems of  FIGS. 90 and 91 ; 
         FIG. 93  is a block diagram of one embodiment of a gain block used in the primary GPS repeater of  FIG. 92 ; 
         FIG. 94  is a block diagram of another embodiment of the gain block of  FIG. 92 ; 
         FIG. 95  is a block diagram of another primary GPS repeater used in the GPS repeater systems of  FIGS. 90 and 91 ; 
         FIG. 96  is a block diagram of one embodiment of a gain block used in the primary GPS repeater of  FIG. 95 ; 
         FIG. 97  is a block diagram of a secondary GPS repeater used in the GPS repeater system of  FIG. 91 ; and 
         FIG. 98  is a block diagram of one embodiment of a gain block used in the secondary GPS repeater of  FIG. 97 . 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  illustrate a preferred embodiment of a flat-panel repeater, having a pair of flanged radomes  10  and  11  on opposite sides of a choke frame  12 . Adjacent the inside surface of the radome  10  is a dielectric sheet  13  carrying four printed dipoles  14  that form the mobile-facing antenna for the mobile side of the repeater. The electronics for connecting the antenna to the necessary diplexers, filters, and power amplifiers are contained within a metal housing  15 , and the antenna sheet  13  is fastened to one side of the housing  15 . The antenna feed  16  is connected directly to one of the diplexers in the electronic circuitry, which will be described in more detail below. The housing  15  is captured within the choke frame  12 , which forms multiple, spaced, concentric fins  72   a - 72   d  for improving the side-to-side (antenna-to-antenna) isolation of the flat-panel repeater, thereby improving the gain performance or stability margin (the difference or safety margin between isolation and gain). The structure of the fins  72   a - d  will also be described in more detail below. 
     The antenna elements on the opposite side of the repeater are mounted adjacent the inside surface of the radome  11 . Thus, a pair of dipoles  14   a  are printed on a dielectric sheet  13   a  to form the base-station-facing antenna for the base-station side of the repeater. The antenna feed  16   a  is connected directly to one of the diplexers in the electronic circuitry, as described in more detail below. The dielectric sheet  13   a  is fastened to the opposite side of the metal housing  15  from the sheet  13 . As can be seen in  FIG. 2 , the dipoles  14  are orthogonal to the dipoles  14   a  to improve isolation between the two antennas. 
     To facilitate mounting of the repeater on a flat surface, a mounting bracket  17  has a stem  18  that fits into a socket  19  in the frame  12 . The bracket  17  has several holes through it to receive screws for attaching the bracket  17  to the desired surface. Electrical power can also be supplied to the repeater through power supply lines (not shown) passing through the mounting bracket  17  and its stem  18  into the frame  12 . The interface between the frame  12  and the bracket stem preferably allows rotation between the frame  12  and the mounting bracket  17  in successive angular increments, such as 5′ increments, to facilitate precise positioning of the repeater. For example, the repeater might be rotated through successive increments while monitoring the strength of the received and/or transmitted signals, to determine the optimum orientation of the repeater, e.g., in alignment with a broadcast antenna whose signals are to be amplified and re-broadcast. Conventional detents can be used to indicate the successive increments, and to hold the repeater at each incremental position until it is advanced to the next position. 
     As can be seen in  FIG. 1 , the flat-panel repeater comprises a closely spaced stacked array of planar components that form a compact unit that can be easily mounted with the antennas already aligned relative to each other. The height and width of the unit are a multiple of the thickness dimension, e.g., 7 to 8 times the thickness. The thickness dimension is preferably no greater than about six inches, and the greater of said height and width dimensions is preferably no greater than about two feet. It is particularly preferred that the thickness dimension be no greater than about three inches, and the greater of said height and width dimensions no greater than about 1.5 feet. Most preferably, the thickness dimension is no greater than about two inches, and the greater of the height and width dimensions is no greater than about one foot. 
       FIGS. 3 and 4  illustrate a flat-panel repeater  20  having a pair of flat radomes  21  and  22  on opposite sides thereof. Each radome  21  and  22  covers one or more antenna elements for receiving and transmitting signals on opposite sides of the repeater. In the illustrative embodiment, the antenna elements are the patches of patch-type antennas, but it will be understood that alternative antenna elements such as dipoles or monopoles may be used. As can be seen in  FIG. 4 , a pair of patches  23  and  24  are printed on a dielectric plate  25  mounted adjacent the inside surface of the radome  21 . The dielectric plate  25  seats in a recess  27  formed by a metal plate  28  that also forms a ground plane for the patches  23  and  24 . The plate  25  seats on multiple plastic standoffs  27   a  connected to the plate  28  within the recess  27 , and a pair of coaxial connectors  27   b  extend through the plate  28  for connection to the patches  23  and  24 . The inner conductors of the connectors  27   b  are connected to the patches  23  and  24 , while the outer conductors are connected to the ground plane  28 . The opposite ends of the connectors  27   b  are connected to the RF circuitry on the board  36 . Because the dielectric plate  25  is recessed within the ground plane, the patches  23  and  24  are substantially flush with the surface of the ground plane. 
     It can be seen that the ground plane formed by the metal plate  25  is considerably larger than the antenna patches  23  and  24 , and the patches are positioned in the central region of the ground plane. These features offer significant advantages in improving the isolation between the two antennas, which in turn improves the gain performance or stability margin of the repeater, as will be discussed in more detail below. In general, the ratio of the total ground-plane area to the central area occupied by the antenna elements is in the range of about 2 to 5, and is preferably about 5, to achieve the desired isolation. 
     The repeater  20  includes a three-part frame, consisting of a central frame member  29  and a pair of RF-choke frames  30  and  31  attached to opposite sides of the central member  29 . The periphery of the ground-plane plate  27  is captured within a slot in the inner periphery of the choke frame  30 . The central frame member  29  is essentially closed on one side by an integral wall  32  that forms a bottom ground plane, and the interior of the member contains several electronic units (e.g., printed circuit boards) and a power connector  33 . A top ground-plane plate  34  closes the open side of the frame member  29 , and is attached to a peripheral flange  35  on the frame member  29 . A second group of electronic units are mounted on a board  36  attached to the outside of the ground-plane plate  34 . 
     The antenna elements on the opposite side of the repeater are mounted adjacent the inside surface of the radome  22 . Thus, a pair of patches  37  and  38  are printed on a dielectric plate  39  seated in a recess  40  formed by a metal plate  41  that also forms a ground plane for the patches  37  and  38 . As can be seen in  FIG. 4 , the patches  23 ,  24  are orthogonal to the patches  37 ,  38  to improve isolation between the antennas on opposite sides of the repeater. The periphery of the ground-plane plate  41  is captured within a slot in the inner periphery of the second choke frame  31 . The patch plate  39  seats on multiple plastic standoffs  40   a  connected to the plate  41  within the recess  40 , and a pair of coaxial connectors  40   b  extend through the plate  41  for connection to the patches  37  and  38 . The inner conductors of the connectors  40   b  are connected to the patches  37  and  38 , while the outer conductors are connected to the ground plane  41 . The opposite ends of the connectors  40   b  are connected to the RF circuitry on the board  36 . Multiple gaskets G are provided for sealing purposes. 
     An antenna is (simplifying somewhat) a path by which electrons get accelerated back and forth (i.e. a “race-track”). For example, in a dipole antenna, electrons accelerate from one end, towards the center (where they have the greatest velocity), then de-accelerate towards the other end (where the velocity is the slowest). They then turn around and accelerate back the other way. They do this at the rate of the resonant frequency of the antenna. The feed point of the antenna (for a dipole, at the center) is the position in which the electrons are moving the fastest. Thus, voltage (potential) of the antenna is tapped from this position. Electromagnetic energy therefore radiates from the ends of an antenna element (dipole or patch) in the direction of the accelerating electrons. This direction is called the antenna polarization (direction). Displacement currents (virtual electrons) therefore go from one end of the dipole, curve out in space, and terminate at the other end of the dipole. For two adjacent antennas, oriented in the same direction, where one is transmitting (active) and the other is receiving (passive), the active antenna pushes virtual electrons into space which terminate on the passive antenna. These virtual electrons then force the actual electrons on the surface of the passive antenna to accelerate, and induce a potential at its feed point. However, if the two antennas are not oriented in the same direction (being orthogonal . . . or perpendicular; for instance) then the active antenna cannot accelerate electrons on the other (passive) antenna. The “race-track” on the passive antenna is extremely short. These antennas are considered orthogonal, and therefore do not couple. Orthogonal antennas, on opposite sides of the repeater, do not couple and therefore appear isolated from each other. Thus, the system gain is increased without inducing ringing. 
     The RF electronic circuitry and antennas for the repeaters of  FIGS. 1-4  is illustrated in more detail in  FIGS. 5-8 . Two different system architectures are shown in  FIGS. 5 and 6 .  FIG. 5  shows an architecture for a two-antenna system, in which each of two antennas  52  and  54  operates in both the transmit and receive modes. For example, the first antenna  52  might be used to receive incoming RF signals from, and transmit signals to, a transmitter or another repeater, that is, in the link mode. The other antenna  54  would then be utilized in the broadcast/repeat mode to transmit signals to, and receive signals from, the user equipment, such as a remote handset or terminal, or to transmit a signal to a further repeater in a system using multiple repeaters to broadcast or distribute signals. 
     An electronics module  60  connected to both antennas  52  and  54  includes a pair of frequency diplexers (D)  61 ,  62  to effectively connect received signals from either antenna to only the receive circuitry for that antenna and not to the transmit circuitry for that same antenna, and to effectively connect transmit signals from the transmit circuitry to only the antenna and not to the receive circuitry for that same antenna. For example, RF signals received by the antenna  52  are routed through the diplexer  61  to a receive path that includes a filter  63  to attenuate the reverse link band, an amplifier  64  to amplify the RF, and then another filter  65  to protect the amplifier  64  from signal power on the other path. The second diplexer  62  then delivers the signal to the antenna  54  which re-transmits the amplified signal. In the reverse direction, the antenna  54  receives signals that are fed through the diplexer  62  to a second path including similar filters  66 ,  67  and a similar amplifier  68  which operate in the same manner as the first circuit to feed signals through the diplexer  61  to be transmitted at the antenna  52 . 
       FIG. 6  shows a four-antenna architecture that includes two pairs of antennas  52   a ,  54   a  and  52   b ,  54   b  on opposite sides of the repeater. The antennas  52   a ,  52   b  on one side may be used for the link mode, as described above, one as the downlink antenna and one as an uplink antenna. Similarly, the two antennas  52   b ,  54   b  on the other side may be used in the broadcast/repeat mode, as described above, one as an uplink antenna and one as a downlink antenna. Similar electronic circuits or paths including filters and amplifiers are interposed between the respective pairs of antennas  52   a ,  54   a  and  52   b ,  54   b . However, because separate pairs of antennas are provided, no frequency diplexers are required in this case. 
     The filters  63 ,  65 ,  66 , and  67  are band pass filters selected to reduce the out-of-band signals. For a PCS-based system, the typical band pass bandwidth is approximately 15 MHz, commensurate with the bandwidth of PCS bands C, D, E, F, etc. Cut off and roll-off are performance and specification oriented, and depend on the circuit design. 
     In one embodiment, the amplifiers  64 ,  68  comprise relatively low power, linear integrated circuit chip components, such as monolithic microwave integrated circuit (MMIC) chips. These chips may comprise chips made by the gallium arsenide (GaAs) heterojunction transistor manufacturing process. However, silicon process chips or CMOS process chips might also be utilized. 
     Some examples of MMIC power amplifier chips are as follows: 
     1. RF Microdevices PCS linear power amplifier RF 2125P, RF 2125, RF 2126 or RF 2146, RF Micro Devices, Inc., 7625 Thorndike Road, Greensboro, N.C. 27409, or 7341-D W. Friendly Ave., Greensboro, N.C. 27410; 
     2. Pacific Monolithics PM 2112 single supply RF IC power amplifier, Pacific Monolithics, Inc., 1308 Moffett Park Drive, Sunnyvale, Calif.; 
     3. Siemens CGY191, CGY180 or CGY181, GaAs MMIC dual mode power amplifier, Siemens AG, 1301 Avenue of the Americas, New York, N.Y.; 
     4. Stanford Microdevices SMM-208, SMM-210 or SXT-124, Stanford Microdevices, 522 Almanor Avenue, Sunnyvale, Calif.; 
     5. Motorola MRFIC1817 or MRFIC1818, Motorola Inc., 505 Barton Springs Road, Austin, Tex.; 
     6. Hewlett Packard HPMX-3003, Hewlett Packard Inc., 933 East Campbell Road, Richardson, Tex.; 
     7. Anadigics AWT1922, Anadigics, 35 Technology Drive, Warren, N.J. 07059; 
     8. SEI Ltd. P0501913H, 1, Taya-cho, Sakae-ku, Yokohama, Japan; and 
     9. Celeritek CFK2062-P3, CCS1930 or CFK2162-P3, Celeritek, 3236 Scott Blvd., Santa Clara, Calif. 95054. 
       FIGS. 7 and 8  show the choke frame of  FIGS. 1 and 2  in more detail. This frame is generally rectangular in configuration and includes multiple fins  70  extending orthogonally outwardly from opposite sides of central flat support members  71  and  72 . As can be seen most clearly in the sectional view in  FIG. 8 , the fins  70  become progressively shorter in the axial direction, and the space between adjacent fins becomes progressively smaller, proceeding from the radially outermost fins  70   a  to the innermost fins  70   d . The fins preferably have height and spacing dimensions related to one-fourth wavelength at the center frequency of the frequency band being amplified and re-transmitted by the repeater, e.g., the height or projection of the fins relative to the sides of the housing may be on the order of a quarter wavelength. In addition, strips of radio frequency absorber material  74  may be located intermediate some or all of the fins  70  about the peripheral surfaces of the main body of the choke frame. Absorber material is typically a low density dielectric loaded with conductive particles or fibers of carbon or metal, and can even be “tuned” to absorb certain frequencies more than others. 
       FIG. 9  illustrates in more detail the peripherally extending fins  73  that form the RF choke between the antennas on opposite sides of the flat-panel repeater of  FIGS. 3 and 4 . These fins  73  comprise relatively thin strips of conductive material located around the periphery of the RF choke frame.  FIGS. 10-13  illustrate alternate embodiments of RF chokes of various forms. 
     In  FIGS. 10 and 11 , the RF choke is formed by a series of concentric annular rings  75  which extend generally orthogonally relative to the plane of the antenna and around the periphery of the antenna, in contrast to the radially extending fins described above. As can be seen mostly clearly in the sectional view of  FIG. 11 , the choke rings  75  are formed by a corrugated metal annulus in which the outer wall  75   a  is slightly shorter than the first full corrugation crest  75   b  in the axial direction, and then the successive corrugation crests  75   c  and  75   d  become progressively shorter in both the axial and radial directions. 
     The circular choke configuration of  FIGS. 10 and 11  has the advantage of providing feedback paths of equal length between all points on the peripheries of the antennas on opposite sides of the repeater. Unwanted feedback occurs via surface currents on the outside surfaces of the panel, and path lengths that are odd multiples of one-half wavelength produce cancellation of the unwanted surface currents. The circular configuration facilitates a choice of dimensions that achieve the desired cancellation of feedback currents because of the uniformity of the lengths of the feedback paths between the two antennas with such a configuration. In general, the repeater is sized and configured for a selected frequency band having a predetermined center frequency and wavelength “X”; the height, width and thickness dimensions of the repeater are selected so that feedback energy at the wavelength “X” travels a feedback path of predetermined length around the repeater to improve the side-to-side isolation. 
       FIGS. 12 and 13  illustrate a circular configuration for a choke structure similar to that shown in  FIGS. 8 and 9 . Multiple fins  80  extend orthogonally outwardly in the axial direction from opposite sides of central flat support members  81  and  82 . As can be seen most clearly in the sectional view in  FIG. 13 , the fins  80  become progressively shorter in the axial direction, and the space between adjacent fins becomes progressively smaller, proceeding from the radially outermost fins  80   a  to the innermost fins  80   d.    
     In an alternative embodiment, a reduced surface wave (RSW) type of antenna structure might be utilized in place of the patch antennas shown in the prior figures.  FIGS. 14 and 15  are a side sectional view and a top plan view of one example of a probe-fed, shorted annular ring, reduced surface wave patch antenna  460 . An RSW patch antenna element, is simply a patch that focuses more energy in the directed area, and not to the sides near the ground plane. There are many types of RSW patches, but the most common is a recessed patch inside a partial cavity. The cavity walls act as a field suppressor, and “catch” field lines that are directed to the sides of the patch, rather than in a direction perpendicular to the patch and ground plane. If both patches (on opposite sides of the repeater) are RSW patches, then they have reduced coupling (i.e. greater isolation), which allows the system active gain to be increased. 
     RSW microstrip antennas produce only a small amount of surface-wave radiation. In addition, if printed on electrically thin substrates, these antennas only weakly excite lateral waves (space waves that propagate horizontally along the substrate interface). As a result, these antennas do not suffer from the deleterious effects of surface and lateral wave scattering. These characteristics make the RSW antenna ideal for applications where the supporting substrate or ground plane of the antenna is small, in which case diffraction of the surface and lateral waves from the edges of the structure may be quite significant for conventional microstrip patch antennas. RSW antennas may also be useful for array applications, where the presence of surface and lateral waves for conventional patch radiators produce significant mutual coupling and may lead to scan blindness. 
     For a given size antenna element (patch, dipole, etc.), increasing the size of the ground plane behind the element reduces the Front to Back (F/B) ratio of the antenna. More specifically, the larger the ground plane, the less energy radiated to the back side. Thus, increasing the size of the faces of the side-to-side repeater reduces the amount of energy that each face radiates to the backward face. Another way of explaining this is that by increasing the size of the repeater, the lower the coupling between the antennas on opposite sides of the repeater (i.e. patches). This therefore increases the isolation between the antennas, and allows the active gain for the system to be increased. However, where the size of the ground plane is limited by other considerations, the RSW patch technology may be employed. 
     A preferred RSW design is the Shorted-Annular-Ring Reduced-Surface-Wave (SAR-RSW) antenna. One example of this type of antenna, shown in  FIGS. 14 and 15 , is a conventional annular ring microstrip antenna  462  with an inner boundary  464  short-circuited to a conducting ground plane  466 . The outer radius dimension is chosen to eliminate surface-wave excitation from the equivalent ring of magnetic current at the outer edge of the antenna that corresponds to the TM.sub.011 cavity patch mode. (The modes are denoted using the notation TM.sub..phi.rho..) The inner radius is chosen to make the patch resonant at the design frequency. 
       FIGS. 16 and 17  diagrammatically illustrate repeater modules  50  and  50   a  with patch antennas that correspond respectively to the systems described above. In these examples, microstrip patches are used for the antenna elements  52 ,  54  ( FIG. 16) and 52   a ,  52   b ,  54   a ,  54   b  ( FIG. 17 ). The module/box or housing  50 ,  50   a  may contain a DC power supply or DC power converter, amplifiers, filters and diplexers (if required), as described above. The electronics may be discrete parts, connected together via SMA connectors. For lower power systems, the electronics can be surface mount PCB. A small lamp, LED, or other display element  100  can be used with appropriate RF power sensing electronics  80  (see  FIGS. 5 and 6 ) to aid the provider/user/customer in orienting the unit or module  50  or  50   a  with a link antenna directed/pointed towards a base station, such that sufficient signal power is being received, i.e., at or above some predetermined threshold. 
       FIG. 18  illustrates an approach which uses an array of antenna elements in order to increase the passive gain. The example shown in  FIG. 18  uses two columns of patch array antenna elements on one face of the module, designated by reference numerals  54   a  through  54   h . The antenna patches  54   a  through  54   d  are designated as receive (Rx) elements in the embodiment shown in  FIG. 18 , while the antenna elements  54   e  through  54   h  are designated as transmit (Tx) elements in this embodiment. It will be appreciated that a similar array of antenna elements, corresponding to the antenna elements  52  of the prior embodiments, are mounted to the opposite face (not shown) of the module  50   b  of  FIG. 18 . Moreover, fewer or more array elements might be utilized in other patterns than that shown on  FIG. 18 , without departing from the invention. 
     In the embodiment shown on  FIG. 18 , the use of four elements, which are summed together in an array, achieves approximately four times (6 dB) the gain of a single receive or transmit element. Thus, with four elements also on the opposite face (not shown), this adds a total of 12 dBi of additional passive gain to the system, which can be used to reduce the required active gain by as much as 12 dB and also to reduce the required isolation by as much as 12 dB. While the near-field wave mechanics might not permit a full 12 dB to be achieved, nonetheless, some considerable improvement can be expected from this approach. The vertical beam width of the system will be reduced somewhat by this approach. 
     The antennas on opposite sides of the repeaters described above are “fixed” in position and orientation to assure maximum isolation between the antennas and to receive and transmit a given signal, and therefore maximize system gain. This isolation between antennas is controlled/maximized (and mutual coupling minimized) in the following ways: 
     a) The two antennas (or sets of antennas) are positioned such that for each, the F/B ratios sum to a maximum. For example, for a perfectly rectilinear module, the two antennas (or sets of antennas) each face oppositely by 180 degrees, or within an acceptable tolerance. 
     b) The two antennas of each path, are polarized in mutually orthogonal (perpendicular) directions, which further reduces the mutual coupling (increases the isolation) by roughly 20 to 30 dB. 
     c) Electromagnetic choke or shunt elements are provided on the edges or borders of the module or housing structure to absorb (shunt) power to ground. Alternatively, the four sides of the housing (i.e., excluding the two sides on which the antennas are mounted) may be composed of metallic material and grounded so as to shunt stray electromagnetic energy to ground. 
     Design of the antennas, beams, and (control of) F/B ratios assures adequate isolation between the two opposing antennas (or antenna sets). The antennas&#39; F/B ratios or isolation is the largest limiter for the total system gain. If desired, the isolation can be further improved by having the wireless connection to the base station on a different frequency band from the remote connection. 
     The above described repeater modules can be used in a number of applications, a few examples of which are as follows. 
     1) Indoor Repeater (see  FIG. 19 ) 
     The flat-panel repeater can be mounted on a wall or window, at or near a location where the RF signal power from a nearby base station is at its maximum power level (within the building). Power for each repeater can be supplied via either a 120-volt cord and plug  102 , or with a 120-volt plug connection  104 , built directly into the repeater (see  FIGS. 20 and 21 ). Both allow very simple installation, by the customer. Generally, the RF signal is received, at a power level above the noise floor, from a nearby base station (with the module placed in a location facing the base station), and the repeater re-radiates the (amplified) RF signal into the building. Additionally, signals from remote units (handsets/cellphones) within the building are received by the repeater, amplified, and re-radiated back to the base station  200 . 
     2) Daisy-Chained Indoor Repeater (see  FIG. 22 ) 
       FIG. 22  shows a plurality of flat-panel repeaters  50  or  50   a  placed at various locations within a building, “daisy chained” together, to provide greater coverage within the building. This aids in providing coverage to the side of the building opposite to the base station, or any other RF null or “blank” areas within the building. In this way, the provider or customer can cheaply and easily install two or more repeaters, to provide coverage to various areas of the building, such as the side opposite the side nearest the base station, where the RF signal level (from the base station) has low Signal to Noise (ratio), or where there is no signal at all. 
     If it is desired to distribute multiple wireless services within a building, such as PCS, MMMDS, LMDS, wireless LAN, cellular telephone, etc., all such signals may be supplied from their receiving antenna(s) to an Ethernet hub before entering the daisy-chained indoor repeaters, as illustrated in  FIGS. 23   a  and  23   b . A separate antenna  110  and electronic circuits  111  are provided for each wireless service, and all the circuits  111  are connected to an Ethernet hub  112 . Each of the circuits  111  includes a frequency converter for converting signals from the frequency used by the wireless service to an Ethernet frequency. The Ethernet hub  112  controls the forwarding of the signals from the multiple wireless links to the single wired connection from the Ethernet hub  112  to an indoor flat-panel repeater  113 , which then relays those signals on to other repeaters such as repeaters  114  and  115  located throughout the interior of the building. 
     Each of the repeaters  114  and  115  has two antennas on the downlink side. Specifically, a first antenna  114   a  on the repeater  114  is designed to produce a beam  117  aligned with the next repeater  115 , while a second antenna  114   b  produces a beam  118  that extends laterally through the adjacent portion of the interior of the building to reach all the users in that portion of the building. For user devices that are not part of an Ethernet, such as PCS subscriber units, the signals from the second antenna  114   b  are received by an Ethernet-to-PCS conversion unit  119  shown in more detail in  FIG. 23   b . This conversion unit includes an antenna  119   a  that complies with the IEEE 802.11 standard, a DSP  119   b , an RF conversion circuit  119   c  for converting the frequency of received signals to the PCS frequency, and a PCS antenna  119   d  for transmitting the converted signals to PCS users in the building. Of course, the conversion unit  119  also works in the reverse direction, receiving PCS signals from subscriber units at the antenna  119   d , converting them to the Ethernet frequency in circuit  119   c , and transmitting them from antenna  119   a  to the repeater  114  for re-transmission back to the repeater  113  and the Ethernet hub  112  which selects the appropriate circuit  11  and antenna  110 . 
     3) Outdoor Null Fill Repeater 
     A single flat-panel repeater can be installed on a tower, instead of a more conventional repeater installation requiring discrete antennas. This provides a smaller, more economical package, and less labor (time) and effort in orienting the antennas to assure adequate isolation between the antennas. 
     4) Outdoor Repeater to Building 
     A single flat-panel repeater can be installed on a tower, in the same fashion as above, realizing the same benefits. 
     The applications mentioned above in 1)-4) are independent of frequency band. That is, any of these applications might be used in any frequency band, including, but not limited to, the following: 
     a) Cellular (800 MHz band) 
     b) PCS (1800 and 1900 MHz bands)—(Personal Communications Service) 
     c) GSM (900 and 1800 MHz bands)—(Global System for Mobile communications) 
     d) MMDS (2500 MHz band)—(Multi-channel Multipoint Distribution Service) 
     e) LMDS (26 GHz band)—(Local Multipoint Distribution Service) 
     f) Bluetooth Applications (2400 MHz band)—(Bluetooth is the name of a wireless protocol standard, created by Ericsson) 
     g) Indoor Wireless LANs (2400 MHz band)—(Local Area Network) 
     h) 3G (3rd Generation PCS systems) at 1900 MHz (U.S.) and 1800-2200 MHz (Europe) 
     If it is desired to increase the wide-angle coverage of the signals re-transmitted by the repeater, one side of the repeater may be provided with multiple antennas oriented in different directions. 
       FIG. 24  shows a block diagram of one path through a repeater system. The input signal, S(t), either from the base station (for the downlink path), or from the mobile user (for the uplink path), is received via an antenna  120 , bandpass filtered at  126   a , amplified at  128  (with active gain=G), filtered again at  126   b , and finally transmitted by an antenna  122 . Some of the transmitted signal energy couples back (through space, or through the electronics) into the receive antenna. This is denoted in  FIG. 24  as the feedback signal, f(t), which is simply a delayed version (attenuated) of the original signal, S(t). Therefore, the composite signal, S(t)+f(t), is fed into the amplifier, with output G(S(t)+f(t)). Assume, for example, that the antennas have 0 dBi gain, then the new feedback signal is G f(t). The propagation of this signal, back to the input antenna, will incur attenuation, H. Therefore, the amplified, attenuated signal at the input antenna will be H G f(t). If this signal is comparable in power to the original signal S(t), then the amplifier  128  will go unstable, and oscillate (ring). This oscillation will cause severe distortion in the desired signal. 
       FIG. 25  shows the same circuit as  FIG. 24 ; however, adding an adaptive cancellation circuit  140 . The goal of this circuit  140  is to create a inverse f(t) signal-f(t) (a 180 degree shifted f(t) signal), and sum it with the input signal, including the feedback signal, f(t), at a summing junction  145 , and thereby remove the feedback signal f(t). 
       FIG. 26  shows a general block diagram (high level) of one form of the adaptive cancellation circuit  140 . In this approach, the input (RF) signal is summed at the junction  145  with a modulated signal constructed via a digitally adaptive process, to destructively interfere with the feedback signal embedded in the input composite signal. After the summation, the composite signal, S(t)+f(t), is digitally sampled and digitally processed via a digital signal processor (DSP)  150 , which computes an intermediate signal for a modulator  152 . The modulator  152  takes the intermediate signal, and a sample of the amplified (output) signal, and creates a near copy of the correct inverted f(t) signal-f(t). This process will work with many, if not most, of the digitally adaptive algorithms for feedback control. Additionally, this methodology does not require an injected signal (training or pilot tone, or wideband noise), for the adaptive process. 
       FIG. 27  shows the circuit  140  in further detail. The DSP  150  is a combination of an RF downconverter  160  to shift the signal to an intermediate frequency that allows digital sampling, an analog-to-digital (A/D) converter  162  which digitizes the analog signal, and a processor  164  which performs the required operations to compute the intermediate signal. The modulator  152  is a combination of a controllable attenuator  166 , and an I/Q modulator  168 . Additional details shown in  FIG. 27  include respective couplers  172  and  174  which couple the signals from the signal paths to and from the adaptive cancellation circuit  140 , a first coupler  172  being interposed between the summation junction  145  and the filter  126  and the second coupler  174  being at the output of the power amplifier  128 . In addition to the couplers  172  and  174 , respective delay lines  182  and  184  may be employed at either end of the RF path, one just prior to the summing junction  145  and one subsequent to the coupler  174 . 
       FIG. 28  shows a block diagram of a repeater system using adaptive cancellation (AC) circuit  140 , details of which are shown in  FIGS. 26 and 27 . The “direction” of the circuit  140  in each RF path has been taken into account. In this system, each (uplink, downlink) path has a separate AC circuit block  140 , and the system uses diplexers  130  because it has only one antenna on each side of the repeater. 
       FIGS. 29 and 30  show the directional characteristics of the AC circuit blocks  140 , whether for the downlink or uplink path. The blocks are “mirror images” of one another, differing by the direction of the desired signal, with the arrows  175  denoting the directionality of each circuit  140 . 
       FIG. 31  shows a side-to-side repeater  190  having a body or housing  192  having opposed flat surfaces. To each of these opposed flat surfaces, there is mounted a single patch antenna element  194 ,  196 , respectively comprising the antennas on the mobile-facing side and the base-station-facing side. An equivalent circuit diagram is shown in  FIG. 32 . It will be understood that the circuit components of  FIG. 32 , including the adaptive cancellation (AC) circuits, may be carried in the body or housing  192 . 
     Similarly,  FIG. 33  shows a side-to-side repeater  190   a  having a similar body or housing  192   a  which mounts separate uplink and downlink transmit (Tx) and receive (Rx) patch antenna elements for each of the two antennas. The respective Tx and Rx antennas on one side of the repeater are designated by reference numerals  194   a  and  194   b , while the respective Tx and Rx antenna elements on the other side are designated by reference numerals  196   a  and  196   b . The circuits shown in  FIG. 34  may be mounted to (in) the body (housing)  192   a.    
     As indicated above, the electronics, including the adaptive cancellation circuits, may be carried on/in the body/housing  192 ,  192   a  of the antenna element in the side-to-side repeater structures of  FIGS. 31 and 33 , permitting a tower-top modular repeater installation, in addition to the other advantages 
     As indicated above,  FIGS. 31 and 32  show the case for a single antenna (element) on each side, including frequency diplexers to separate each path (or frequency band).  FIGS. 33 and 34  show the approach when using separate Tx and Rx antennas, and therefore separate circuits, for each (uplink, downlink) path. 
     The above-described approach may be used in a number of applications, including: Cellular Coverage (null fill, in-building systems), PCS, MMDS, WLL and LMDS. 
       FIG. 35  illustrates a typical prior-art repeater implementation  215  residing on a mast or tower  220  and including a base-station-facing antenna  222  for exchanging signals with a base station  224  at a remote location. The base station  224  may include a tower  226 , transmit and receive antennas  228  and base station equipment  230 . A mobile-facing antenna  232  exchanges signals with the subscriber which may be a mobile subscriber as illustrated by an automobile at reference numeral  234 . The antenna  232  may be designed, located and installed so as to provide coverage over a null fill area  236 , as will be described below. The antennas  222 ,  232  are coupled with the repeater electronics  225  which is mounted elsewhere on the mast or tower  220  by runs of coaxial cable  227 ,  229 . 
     Referring now to  FIG. 36 , a repeater implementation in accordance with one embodiment of the invention is designated generally by the reference numeral  245 . Similar to the arrangement in  FIG. 35 , the repeater equipment is mounted to a mast or tower  220  and has a base-station-facing antenna  222  and a mobile-facing antenna  232 . Similar to the arrangement in  FIG. 35 , the antenna  222  communicates with antennas  228  at the base station  224 , and the antenna  232  communicates with user equipment which may be a mobile unit  234  with coverage being provided in a null fill area  236 . Departing from the prior art, the repeater of the invention comprises an integrated repeater system in which the repeater electronics  225  are incorporated into a single unit or module  250  along with the two antennas. 
     Often a major challenge for wireless service providers is getting access to an equipment site situated in an optimum location. As shown in  FIG. 37 , the direction from the base-station-facing antenna  322  of the repeater to the base station  324 , and/or the direction of the mobile-facing antenna  332  to the null site  336  (i.e., the null fill area) is rarely at a right angle to the face of the donor or null antenna. In fact, this angle will vary significantly from site to site. To address this problem, one embodiment of the invention uses an antenna array with a beamformer network that can be programmed, e.g., from a look-up table. This allows the two antennas to be beam-steered toward the location of the base station and null sites. 
     The antennas and beamformer can be implemented in several ways. The block diagrams in  FIGS. 38 and 39  show two possible implementations.  FIG. 38  is an implementation that uses a common antenna for transmit and receive on each side of the repeater.  FIG. 39  shows separate transmit and receive antennas  322   a ,  322   b  and  332   a ,  332   b  on each side of the repeater. The implementation of  FIG. 38  uses duplex filters or diplexers  360 ,  362  to separate the downlink path and uplink path signals for processing by the repeater. This approach has the advantage that the total area on the side of the integrated repeater  350  can be utilized to accommodate a larger antenna array. However, this approach requires that the filters  360 ,  362 , provide all of the isolation between the downlink path and uplink path of the repeater.  FIG. 39  is an implementation that uses separate transmit ( 332   a ,  332   b ) and receive ( 322   a ,  322   b ) antennas and filters  400 ,  402 ,  406   a  and  406   b . This approach also has the advantage of using the isolation of the two antennas to reduce the filtering requirements in the repeater. However, this approach may increase the area required for the antennas on the sides of the repeater. 
     The remaining repeater circuits may be implemented in a number of ways. The embodiments shown in  FIGS. 38 and 39  use a channel-selective approach. In this approach, a Low Noise Amplifier (LNA)  390  amplifies the low-level signal from each of the antennas, and is a very quiet amplifier to ensure that a good signal-to-noise ratio is maintained in the repeater. After the LNA  390 , the desired signal moves to a channel module, comprising an uplink channel module  394  in the uplink path and a downlink channel module  396  in the downlink path. In the channel module, the desired signal is downconverted to a lower intermediate frequency and filtered to limit the spectrum amplified by the repeater to a single channel or set of channels. The intermediate frequency is then upconverted back to the original frequency of the desired signal. The output signal of the channel module is then routed to a power amplifier  398  in each path to create a high level transmit signal. In  FIG. 39 , respective filters  400 ,  402  are provided between the LNA&#39;s and Power Amplifiers and associated beamforming and selection circuits  404 ,  406  (to be described below) for the donor and null antennas. Interference cancellers  408  are connected between the outputs of the power amplifiers and the inputs of the LNA&#39;s. 
     The invention may use a direct RF, offset RF, DSP, or GPS based repeater instead of the above-described channel-selective approach. Examples of DSP and GPS repeaters are shown respectively in copending U.S. patent application Ser. No. 09/460,023, filed Dec. 13, 1999 and Ser. No. 09/513,543, filed Feb. 25, 2000, which are incorporated herein by reference. A direct RF repeater performs all gain and filtering functions at the high frequency of the desired signal. An offset RF or frequency translating repeater is similar to a channel-selective repeater except that the upconversion of the intermediate frequency moves the signal to a new high frequency signal instead of the original frequency of the desired signal. This approach will minimize or eliminate the need for an interference canceller. A DSP repeater will still utilize an LNA and power amplifier, but the processing functions in the channel module are handled by digitizing the desired signal, performing the function digitally and then converting the digital signal back to an analog signal. 
     As shown in  FIGS. 40 and 41 , the antennas  322  and  332  can be implemented using antenna arrays  370 ,  380 . Each antenna array uses a row of M horizontally spaced elements to achieve the desired azimuth beamwidth and N vertically spaced rows of elements to achieve the desired elevation beamwidth. This invention may use many different types of antenna elements in the antenna array. Some examples include patch antennas  372  ( FIG. 40 ) and bow-tie dipoles  382  ( FIG. 41 ).  FIG. 40  is an example of a patch antenna array  370  with M=4 and N=3.  FIG. 41  is an example of a bow-tie dipole array  380  with M=4 and N=2. 
     The beamforming and selection networks  404 ,  406  and  404   a ,  404   b ,  406   a ,  406   b  in  FIGS. 38 and 39 , combine the antenna elements  372  or  382  in the antenna array  370  or  380  with appropriate phase and amplitude to create the desired antenna pattern. Several methods can be used to implement the beamforming and selection networks. One method of implementing this is to use an M×N Butler matrix to perform the phasing and combining functions. The angle and elevation of each beam is stored in a look-up table that the repeater uses to drive a diode or relay switch matrix to select the desired beam. This look-up table is stored in a memory of the repeater controller  410  in order to map the desired azimuth and program other parameters and matrix settings for use by the Butler matrix. 
     One example of a Butler matrix for beamsteering is shown in  FIG. 45 . Here a plurality of antenna elements  800  are arranged in a 3 by 3 array. The antenna elements  800  may be patches  372  such as in  FIG. 40 , dipoles such as the dipoles  382  shown in  FIG. 41  or another form of antenna elements. All the antenna elements  800  in the array are coupled with a two-dimensional Butler matrix  802 . The two-dimensional Butler matrix  802  is in turn coupled with an M:1 radio frequency (RF) switch  804 . In the illustrated embodiment, M=9, the total number of antennas  800  in the array coupled with the Butler matrix  802 . The RF switch  804  is controlled by a controller or control circuit module  806  via a control output  805  which may also control other similar RF switches for the other repeater antenna array via an additional control output  807  as shown in  FIG. 45 . The controller  806  may be a part of the controller  410  of  FIG. 38  or  39 . 
     The controller  806  may be set to sequentially switch to the beams provided by the antenna  800  via the Butler matrix  802  and RF switch  804  to search for an optimal signal, such as the highest net power output. This is indicated in  FIG. 45  by an RF connection  808  from the output of the switch  804  to an input of the control circuit  806  for monitoring the RF output. Other parameters might be used to control switching such as the lowest noise or some other measure of signal quality. Thus, in operation, the control circuit  806  switches antenna elements until an “optimum” signal output is located and then remains connected to the antenna element at which the optimal signal is received. RF circuits similar to that shown in  FIG. 25  are located between the switch  804  and a similar switch (not shown) which is coupled in the same fashion indicated to a similar Butler matrix to select a beam from a similar antenna array (not shown) at the opposite side of the repeater. The control module  806  similarly controls this second RF switch coupled with an antenna array at the other side of the repeater via a control line  807 . The second RF switch may be controlled by the control circuit  806  on the same basis, for example, on the basis of signal strength or some other measure of signal quality. The RF circuit includes respective diplexers  809  (where the respective antenna elements  800  perform both transmit and receive functions), power amplifiers  810  and filters  812 . 
     A system of beamforming or beam selection other than a Butler matrix may also be utilized without departing from the invention. For example, the signal processor or controller  410  (e.g., in  FIG. 38  or  39 ), in addition to its other functions, can be programmed and adapted to perform a continuous variable, essentially linear beamforming function by continuous adjustment of the N beams coming in with a variable phase and amplitude weighting being applied, to develop a single beam direction to correspond to the desired beam direction of either of the antennas for communicating with a base station or subscriber equipment. Various phase and amplitude settings can be prestored for a number of beams, for example N beams, each with a given directional characteristic or setting, from which the processor chooses the best match for a given situation. 
     Another method is to build the phasing and combining networks with variable phase devices in series with each antenna element. A look-up table of phase values for discrete angles and elevations is then used to create the desired beam. In  FIG. 46 , the antenna elements  800  in an N by N (e.g., 3 by 3) array are each coupled with a respective one of a plurality of phase shifters  820 . The phase shifters are in turn coupled via a corporate feed  822  to an RF output A which may couple with the RF circuits as shown in  FIG. 45 . A controller  824  is provided to control all the phase shifters  820 . The same arrangement is utilized for the antenna on the opposite face of the repeater. 
     The latter arrangements differ from the Butler matrix in that only one beam or directional output is developed or generated for a given requirement or situation or relative location. In contrast, in the Butler matrix, a total of N beams are available at all times with a switching network being utilized to select the one of these N beams best suited for a given situation or placement of the repeater tower relative to the base station and null fill area, respectively. 
       FIG. 47  illustrates the flat-panel approach to repeater construction using arrays of antenna elements. For relatively low power applications, a first face  822   a  may mount a plurality antenna elements  800  which may be patches, dipoles or other antenna elements. Similar antenna elements may be mounted in an array on the opposite face  832   a . The relatively thin housing  852   a  between the two faces or surfaces  822   a  and  832   a  may house the electronics. 
     Referring to  FIG. 48  in an alternate design, each of a pair of flat panels  850   b  and  850   c  mount antenna elements (not shown) only on their outwardly facing surfaces  822   b  and  832   b . The two panels  850   b  and  850   c  are pivotally mounted to a pair of brackets  850 ,  852  or other support structure at pivot points  854  and  856  and aligned pivot points (not shown) at the bottom edges of the respective panels  850   b  and  850   c . A separate electronics housing or enclosure  852   b  may be coupled with the brackets or other support structure  850  and  852  intermediate the two flat panels  850   b  and  850   c . The beamsteering may be accomplished by tilting (or rotating) the respective panels until the maximum signal strength, or some other measure of signal quality is achieved. 
       FIGS. 49 and 50  are simplified diagrams illustrating beamsteering via the use of various delay lengths by using striplines of different lengths on different layers of a multi-layer printed circuit board selectable by an RF switch ( FIG. 49 ) or striplines of different lengths printed on the same circuit board and selectable via RF switches ( FIG. 50 ). Thus, in  FIG. 49 , antenna elements  480 ,  482  and  484 ,  486  are each coupled to multiple striplines of different lengths, represented by various solid and broken lines designated generally by the reference numeral  488 . All these lines  488  of various lengths are coupled together at radio frequency (RF) summers  481 . That is, all of the lines  488  of a first length are coupled to one summer  483 , all of the lines  488  of a second length are coupled to a summer  485 , and so forth. A radio frequency (RF) switch  487  operated in response to a control signal on a control line  489  selects from among the lines of different lengths connecting the various antenna elements  480  to the summers  483 ,  485 , etc. The control signal may be produced automatically in response to a measurement of signal strength or some other optimal signal quality, in order to accomplish beamsteering via the selection or adjustment of stripline length. 
     In the approach shown in  FIG. 50 , the selection of striplines  490  of varying length is accomplished at the antenna elements  492 ,  494 ,  496 , etc. by respective radio frequency switches  491 ,  493  and  495 . All these delay lines of varying length feed a common RF output  497 . The delay line length for each antenna may be selected either independently or in unison with the selection of delay lines for other antennas, in response to suitable control signals (C) in much the same fashion as in  FIG. 49 , and/or, as described above, in response to detection of an optimal signal level or some other optimal signal quality measurement. 
     Typically, a repeater site uses the physical separation of the antennas to achieve enough isolation to allow the repeater to operate with gains of 60 to 95 dB. Because the antennas are located relatively close together in the flat-panel repeater, another approach is needed to achieve isolation. As described above, such an approach can include the use of radio frequency chokes in the enclosure between the antennas to reduce the coupling between the antennas, or the use of an adaptive interference canceller to provide additional gain and phase margin, as described above. 
     A limiting characteristic for repeaters is that of the feedback loop, or conversely, the isolation between the two opposing antennas (or sensors). That is, the total front to back (F/B) ratio for the system, or isolation, must be higher than the desired gain. Generally speaking, the isolation between donor and null antennas is equal to the total repeater gain plus some margin, typically around 10 to 15 dB. Therefore, the repeater gain will in general be less than the isolation minus the margin. For example, if the isolation between antennas is around 60 dB, then the maximum repeater gain allowed will be about 45 dB. For PCS frequencies, these figures may result in a repeater range of less than 100 feet. 
     In a scattering environment, which is common in PCS, every 6 dB of additional system gain will double the coverage distance. Thus, obtaining an additional 24 dB of isolation between the two antennas, will allow the range to double 4 times, to 1600 feet. For conventional repeater systems as in  FIG. 35 , where the two antennas and repeater electronics are in three separate enclosures, and locations, the donor antenna (to the base station) and null antenna (to the desired coverage area), are separated in space by (usually) more than 10 feet. This distance adds over 50 dB to the isolation between antennas, generating a total isolation value of well over 100 dB. Therefore, with a 15 dB margin, this type of system can utilize a total gain of up to 85 dB or more, which results in fairly large range and coverage. 
     For the integrated repeater of this invention, where the opposing antennas are in or on the same housing or enclosure, and separated in space by as little as a few inches, isolation is typically limited to a value below 80 dB or so. This therefore allows a total repeater gain of no more than 65 dB, which may limit the system range to a few hundred feet or less. 
     The adaptive cancellation approach removes a significant portion (between 10 dB and 40 dB) of the feedback signal power, therefore increasing the total system isolation by the same amount (10 to 40 dB). This additional isolation can be used to achieve greater repeater gain, and therefore significantly extend the range of the system. This is especially useful in the integrated repeater. 
     Isolation between the two sides of the repeater can also be improved by the use of different sized arrays of antenna elements on the mobile and base station sides to reduce the effect of multipath interference and decrease direct coupling between the two antennas. Thus, an N.times.M array of dipoles on the base station side of the repeater may be sized to provide high gain and a directive beam to limit reflections from nearby objects such as walls and ceilings. For example, a 2.times.2 array might be used. The array spacing may be chosen as a half wavelength at the center frequency of the frequency band being amplified and re-transmitted by the repeater, to produce a null in the array factor on the horizons, thus reducing the direct coupling between the antennas on opposite sides of the repeater. For the broader beamwidth desired on the other side of the repeater, to provide a large coverage area, a linear array of N dipoles may be used. This linear array produces a fan beam with increased directivity in the elevation plane, which acts to reduce the multipath interference due to reflections from nearby objects such as walls or ceilings. The dipole arrays are preferably implemented as twin-line-fed dipoles with tuning stubs for impedance matching. A coax-to-twin-line balun may be implemented with a smooth transition from a microstrip line to a twin line on the same substrate as the antenna and corporate feed, resulting in a compact, low-cost antenna. The dipoles are preferably polarized at a 45.degree. slant for optimum reception of signals of unknown polarization, with opposite slants on opposite faces of the repeater for maximum isolation. As an alternative, antenna elements may be provided on opposite sides of the repeater to produce circularly polarized radiation patterns, preferably of opposed polarities. 
     The microprocessor or controller (repeater controller)  410  provides the repeater control functions. This controller provides all setup, communications, and monitoring functions for the repeater. These functions include those related to setting the beamforming and selection functions to the desired beam, as mentioned above, and setting the amplifier gain and frequency of operation to the maximum usable gain for stability and the power rating of the repeater. 
     The controller&#39;s functions may also include monitoring of power levels at various points in the system, monitoring of the status of the devices in the system, for example for over-power, under-power, oscillation, etc. The controller may also include communication ports for communication with outside devices. For example, a local connection, such as an RS-232 port may be provided to communicate with a laptop computer which may be used in the field to exchange data with the controller, update data or program routines, or the like. A remote communication port or protocol may also be employed to enable communications with a network management system, through a local telephone company or wireless serial communication port, such as a data modem or TCP/IP (Transmission Control Protocol/Internet Protocol) or SNMP (Simple Network Management Protocol). In this regard the controller  410  may comprise a microprocessor with a UART (Universal Asynchronous Receive Transmit) to enable the desired communications and command structures and protocols. 
       FIGS. 42 and 43  are software flow charts for the initialization of the repeater, which includes beam selection on the base-station-facing antenna and the mobile-facing antenna and the initial gain settings. The blocks in the flowcharts of  FIG. 42  and  FIG. 43  are as follows: 
     
       
         
           
               
               
             
               
                   
               
               
                 Reference No. 
                 Function 
               
               
                   
               
             
            
               
                 500 
                 Power On/Reset 
               
               
                 502 
                 Disable Repeater 
               
               
                 504 
                 Get Donor Site Coordinates &amp; Elevation 
               
               
                 506 
                 Get Null Area Coordinates &amp; Elevation 
               
               
                 508 
                 Get Repeater Site Coordinates &amp; Elevation 
               
               
                 510 
                 Get Compass Direction of Repeater 
               
               
                 512 
                 Calculate Pointing Angle to Donor 
               
               
                 514 
                 Get Donor Beamformer Settings From Look-Up Table 
               
               
                 516 
                 Set Donor Beamformer 
               
               
                 518 
                 Calculate Pointing Angle to Null 
               
               
                 520 
                 Get Null Beamformer Settings from Look-Up Table 
               
               
                 522 
                 Set Null Beamformer 
               
               
                 524 
                 Set Repeater Gain to Minimum 
               
               
                 526 
                 Set Repeater Channel Frequency 
               
               
                 528 
                 Enable Repeater 530 Measure Forward Power 
               
               
                 532 
                 Forward Power Over Limit? 
               
               
                 534 
                 Display Warning 
               
               
                 536 
                 Disable Repeater 
               
               
                 538 
                 Increase Gain 6 dB 
               
               
                 540 
                 Measure Forward Power 
               
               
                 542 
                 Forward Power Over Limit? 
               
               
                 544 
                 Forward Power Increase 6 dB? 
               
               
                 546 
                 Decrease Gain 6 dB 
               
               
                 548 
                 Decrease Gain 6 dB 
               
               
                 550 
                 Go to Main Loop 
               
               
                 552 
                 End 
               
               
                   
               
            
           
         
       
     
       FIG. 44  is a software flow chart for a main operational loop of the repeater control program, and includes only the functions related to auto gain control of the repeater. The blocks in the flow chart of  FIG. 44  are as follows: 
     
       
         
           
               
               
             
               
                   
               
               
                 Reference No. 
                 Function 
               
               
                   
               
             
            
               
                 600 
                 Main Loop 
               
               
                 602 
                 Wait Time T1 
               
               
                 604 
                 Measure Forward Power 
               
               
                 606 
                 Forward Power Over Limit? 
               
               
                 608 
                 Decrease Gain 2 dB 
               
               
                 610 
                 Increase Gain 2 dB 
               
               
                 612 
                 Measure Forward Power 
               
               
                 614 
                 Forward Power Increase 2 dB 
               
               
                 616 
                 Decrease Gain 2 dB 
               
               
                 618 
                 Decrease Gain 4 dB 
               
               
                   
               
            
           
         
       
     
     The automatic gain control feature may also be used to monitor undesired feedback and adjust the gain of the appropriate signal amplifier(s) to prevent oscillation. An oscillation detector may also be included to monitor the current flow through the amplifier and produce a signal that can be used to shut down the repeater, or the appropriate circuits in the repeater, in the event that oscillation actually occurs. 
       FIG. 51  shows a solar panel  910  with a battery  911  on a relatively thin, flat antenna  912  of the type described above. The addition of a “solar panel with battery” system allows the repeater to be installed in a location with sunlight, and therefore mitigate the requirements for an external (DC) power source. The system actually operates from the battery unit, which is occasionally (when the sun is up) re-charged from the embedded solar panel unit. This is an excellent application for spot coverage requirements for a repeater, where there is currently not a local power source or wiring. Additionally, it aids the installation of the unit indoors (assuming sufficient lighting, to recharge the batteries, where there is no local power plug). Lastly, it is more aesthetic, than requiring wire runs to the unit. Note that the solar panel can be on the top, sides, and/or the front face (with a hole for the patch antennas). The battery system is inside the unit; adjacent to the RF hardware (amplifiers, etc.). 
     In order to improve the front-to-back isolation between the two antennas of the repeater, the two antennas can also be physically separated from each other by a distance of at least several feet, as illustrated in  FIG. 52 . For example, separating the antennas by only 10 feet equates to a 40-dB propagation loss in the PCS frequency band. In  FIG. 52 , two separate antennas  921  and  922  of a repeater are mounted on the walls  923  and  924  at opposite ends of a room or space within a building and are interconnected by a coaxial cable  925  extending along or within the ceiling  926 . 
     In  FIG. 53 , two separate antennas  931  and  932  are mounted on opposite sides of an exterior wall  933  of a building and are interconnected by a coaxial cable  934  extending through the wall  933 .  FIG. 53   a  illustrates an H-shaped repeater housing  935  that eliminates the need for the coaxial cable  934  in  FIG. 53 , and  FIG. 53   b  illustrates an inverted-U-shaped housing  936  that accomplishes the same result.  FIG. 53   c  illustrates a repeater housing  937  having a central section that not only spaces the two sides of the repeater from each other, but also is shaped to fit over a pole P to facilitate both the mounting of the repeater and the orientation of the antennas on the opposite faces of the repeater. That is, the repeater  937  can be simply rotated around the pole P to the desired angular position.  FIG. 53   e  illustrates another form of inverted-U-shaped repeater housing  938 , and  FIGS. 53   f  and  53   g  illustrate two modified housing structures  939  and  940  adapted to be mounted on a pole P. The housing  939  comprises two sections joined by a coaxial cable  939   a.    
       FIG. 54  illustrates an embodiment in which a pair of diplexers D1 and D2 and an amplifier A are integrated with each of the two antennas  941  and  942  for simultaneous transmission of bidirectional signals between each antenna and a common interconnecting coaxial cable  943 . Alternatively, all the electronics can be integrated with just one of the antennas to further simplify the hardware and reduce the number of diplexers required. 
     Instead of connecting the physically separated antennas via coaxial cable, the physically separated antennas can be coupled wirelessly, using either RF or infrared wireless coupling. The signals arriving at the two antennas from outside the repeater are converted to a different frequency for the local transmission between the two antennas within the repeater, to avoid interference with signals within the system band and thereby improve the total system gain. 
     Referring to  FIG. 55 , within a repeating device  1010 , individual low gain amplification devices (e.g., negative resistance amplifiers  1012 ,  1014 ) that separate input and output signals by their direction of propagation can be connected in circuit with directional antennas  1016 ,  1018  to provide low gain, short range repeating devices or “repeating cells”  1010 . In  FIG. 56 , numerous such repeating cells  1010  are arranged in a parallel fashion within a repeater  1020  such that in the direction of propagation, the signals of all the devices add. Thus, the total gain of the repeating device  1020  is the additive gain of all the individual repeating cells  1010 . This device includes a pair of repeaters  1020  and  1020   b , each constructed of multiple cells  1010  of the type shown in  FIG. 55 . The two repeaters  1020  and  1020   b  may be connected in a “daisy chain” configuration, with one repeater  1020  passing a signal to and/or receiving a signal from the other repeater  1020   b . In practice, these two repeaters are located considerably farther apart than indicated in the somewhat simplified diagram of  FIG. 56 . 
     In each cell  1010 , a hybrid coupler  1015  ( FIG. 55 ) functions to separate the incoming signal from the outgoing signal. Filters  1022  and  1024  are also provided between the hybrid coupler  1015  and the antennas  1016  and  1018 , respectively. The practical isolation of the hybrid coupler is 15-20 dB, which limits the maximum gain of the negative resistance amplifier to 6-15 dB. Useful repeater range typically requires 50 to 60 dB total gain. The directive antennas  1016 ,  1018  can provide 19 dB gain each, and thus each cell can have a gain of as much as 53 dB (19+19+15). Accordingly, the construction of a repeating device or repeater using a plurality of such cells in parallel is capable of providing considerable gain. 
     Moreover, it is possible to construct an individual cell of the generalized configuration of  FIG. 55  with adequate repeater gain to meet the typical gain requirements of a useful repeater. The antennas  1016 ,  1018  can each be a 16 element (4.times.4) flat-panel array. Based on this approach,  FIG. 57  shows one embodiment of the invention in which the repeater  1020  is configured in the form of a rectilinear box housing  1030 , having opposed square (or rectangular) faces  1032  and shorter connecting sidewalls  1036 ,  1038 . Radiating elements, such as a patch element  1016  for each cell  1010 , are arrayed on faces  1032 . The specific shape of the housing may be different from that shown. 
     Referring now to  FIG. 58 , a repeater diversity system in accordance with a further aspect of the invention is employed in a repeater system  1110  mounted on a tower  1112 . At the top end of the tower  1112 , a mobile-facing antenna  1114  and a base-station-facing antenna  1116  are mounted facing in generally opposite directions. Appropriate feeds such as coaxial cables or other suitable feedlines  1118  and  1120  respectively run from the antennas  1114  and  1116  to an electronics enclosure  1122  located at a lower part of the tower  1112 , in which the repeater-associated electronic circuitry is located, which circuitry will be further described in connection with  FIG. 59 . The antenna  1114  generally broadcasts and receives signals relative to a remote user location or subscriber equipment. This subscriber equipment may be mobile equipment such as in a cellular or PCS system, or the like. Thus, the signal source received by the antenna  1114  from the remote equipment may be a mobile signal source. The antenna  1116  transmits and receives signals relative to a base station at some remote location. The repeater electronics  1122  boosts the signals as they are passed between the two antennas, to enhance the communications between the remote source and the base station. 
     As shown in  FIG. 59 , the antenna  1114  includes a main antenna  1130  and a receive (Rx) diversity antenna  1132 . In one embodiment, these two antennas  1130  and  1132  are arranged to have the same phase center but mutually orthogonal polarizations (see  FIG. 61 ). By using this arrangement, the problem of location-induced phase variation is substantially eliminated. This fact can be used to overcome the complications in differential phase variation of the main and diversity signals of a mobile signal source, when the signal source is moving over time relative to the repeater location. 
     In the illustrated embodiment, the main mobile-facing antenna  1130  and the base-station-facing antenna  1116  serve to both transmit and receive signals relative to the remote or subscriber equipment and the base station, respectively. Accordingly, each of these antennas is provided with a frequency diplexer  1140 ,  1142  to accommodate the use of different frequency bands in the uplink and downlink channels. 
     Referring first to the uplink channel  1150 , it will be seen that the receive signals from the main and Rx diversity antennas  1130 ,  1132  are fed through respective low noise amplifier (LNA)/attenuator circuits  1152 ,  1154  and combined at a combining network  1156 . In one embodiment the combining network combines these signals with a fixed phase adjustment. The incoming signal from the Rx diversity antenna  1132  is initially processed by a suitable filter  1158 . The combined signal from the combining network  1156  is further processed by an uplink channel module  1160 , amplified by a power amplifier  1162 , and fed to the donor antenna  1116  via its associated diplexer  1142 . In accordance with one embodiment of the invention, the signals from the main and Rx diversity antennas  1130 ,  1132  are combined at the combining network  1156  with equal gain from the low noise amplifiers  1152 ,  1154 . In the illustrated embodiment, the signals from the antennas  1130  and  1132  are aligned in phase by the combining network  1156  and uplink channel module  1160 , in addition to being combined with equal gain settings on each path. 
     Completing the electronics  1122 , a downlink channel module  1170  receives signals transmitted from the base station via the antenna  1116  and its associated frequency diplexer  1142 , which signals are first amplified by a low noise amplifier (LNA)/attenuator  1172 . The output of the down link channel module  1170  is fed through a power amplifier  1174  to the diplexer  1140  for transmission by the main antenna  1130 . 
     Typically, each channel module includes an upconverter, a filter, and a downconverter. Some gain may also be provided. Suitable channel modules are made by Andrew Corporation, the assignee. 
     In the system of the invention as described above, the two antennas  1130  and  1132  provide two separate versions of the receive signals from the remote or subscriber equipment with statistically independent multipath characteristics, since the vertical and horizontal field components in a communications link are highly uncorrelated. By using receive antennas  1130 ,  1132  that have the same phase center and mutually orthogonal polarizations, differential phase variations induced by the changing location of a mobile remote source are substantially eliminated. This overcomes the usual challenge of equal gain combining which requires that the two diversity paths be aligned in phase, since phase alignment would normally be made difficult by the changing location of the mobile signal source. 
     Advantageously, the invention makes possible the implementation of receive diversity in a repeater being used in a wireless communication system. The implementation of receive diversity in a repeater is not limited to a single type of system (e.g., CDMA) but could be implemented for any digital- or analog-based wireless communications system. The invention provides, on average, a 2.5 to 3 dB increase in the average carrier-to-noise ratio of the received signal. 
     Rather than a single main mobile-facing antenna and a signal base-station-facing antenna as described above, with frequency diplexers, the repeater may employ separate transmit and receive antennas on both sides, utilizing separate signal paths in amplification therebetween. Such an arrangement is shown in  FIG. 60 . In this case, the signal from the main receive antenna  1130   a  combined with the signal from the receive diversity antenna  1132  at the combiner  1156 , after bandpass filtering at filters  1140   a ,  1158  and equal gain amplification at LNA&#39;s  1152 ,  1154 . 
     In the case of separate transmit and receive base-station-facing antennas, an LNA  1172  receives signals from the antenna  1116   b  which it transmits through a down link channel module  1170 , power amplifier  1174  and bandpass filter  1140   b  to the antenna  1130   b . Similarly, the main mobile-facing receive antenna  1130   a  delivers received signals to an LNA  1152  (after bandpass filter  1140   a ), which, upon being combined with signals from the Rx diversity antenna  1132  at a combining network  1156  and processed at an uplink module  1160 , are delivered via a power amplifier  1162  and transmit bandpass filter  1142   a  to a transmit antenna  1116   a  for transmission to the base station. 
     In one specific example of a CDMA repeater system, the uplink module  1160  employs a channelizer having a gain of about 24 dB or greater for an uplink path channel in a frequency range from 1850 to 1910 MHz. Similarly, the downlink module  1170  utilizes a channelizer having a gain of at least 24 dB for a downlink path channel in a frequency range of 1930 to 1990 MHz. In this embodiment, the gain of the low noise amplifiers  1152  and  1154  is 33 dB or greater, and the gain of the power amplifiers  1162  and  1174  is 43 dB or greater. 
       FIG. 62  is a block diagram showing the use of a typical RF Butler matrix  1220 . These devices are used in analog communication to generate multiple antenna beams, from a composite antenna system having a plurality of antenna elements  1222 . Butler matrices can be purchased complete, or generated from a composite circuit of 90 degree hybrids and RF summer circuits. In  FIG. 62 , a total of M antennas, each with similar characteristics, are used as the input to the Butler matrix. The Butler matrix device then generates K unique RF (analog) outputs  1224 , each for a respective beam direction. 
     Equation (1) below is a general empirical equation (model) for an M-point Discrete Fourier Transform (DFT). This type of transform is normally used in digital technologies to derive the frequency response, X(k), for a series of time domain inputs, x[i]. For example, a Fast Fourier Transform (FFT) is simple a radix-2 DFT. Thus, the FFT (or DFT) transforms the time domain response into a frequency domain response. 
     
       
         
           
             
               
                 
                   
                     
                       X 
                       ⁡ 
                       
                         ( 
                         k 
                         ) 
                       
                     
                     = 
                     
                       
                         1 
                         M 
                       
                       ⁢ 
                       
                         
                           ∑ 
                           
                             i 
                             = 
                             1 
                           
                           M 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             x 
                             ⁡ 
                             
                               [ 
                               i 
                               ] 
                             
                           
                           ⁢ 
                           
                             ⅇ 
                             
                               
                                 - 
                                 
                                   j 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       
                                         2 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         π 
                                       
                                       M 
                                     
                                     ) 
                                   
                                 
                               
                               ⁢ 
                               
                                 k 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     i 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     j 
                     = 
                     
                       
                         - 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Similarly, the Butler matrix acts as a transform from the spatial response, x[i], to the sectored (or beam) space response, X(k). 
       FIG. 63  shows an example of a beam pattern for one of the spatial elements (or antennas)  1222  from  FIG. 62 . Each antenna has a 120 degree sector beamwidth, or Half Power Beam Width (HPBW). The base-station-facing antenna preferably has a narrower half power beamwidth than the mobile-facing antenna. For example, the beamwidth of the base-station-facing antenna is typically about 30 degrees, plus or minus 5 degrees, while the beamwidth of the mobile-facing antenna is about 60 degrees, plus or minus 10 degrees. 
       FIG. 64  shows four (4) similar antennas  1222  feeding a Butler matrix  1220  in a similar configuration to  FIG. 63 . Each input antenna has a similar 120 degree HPBW, as shown in  FIG. 63 . For this case, M=4 in equation (1) above. The Butler matrix is therefore a 4-port device, with 4 input ports and 4 output ports. The output ports  1224  in  FIG. 64  are labeled with a numerical designation for the RF output for each beam, corresponding to the numerical designation of the antenna elements  1222  at the input ports. 
       FIG. 65  shows the azimuth beamwidth response for the Butler matrix in  FIG. 64 . Each beam has a beamwidth equivalent to roughly 120 degrees divided by four (or M), which is roughly 30 degrees. Additionally, the direction for each of the 4 output beams is uniformly spaced by about 30 degrees. Therefore, the Butler matrix transforms the response of 4 wide angle antennas, all pointing in the same direction (thus all “seeing” exactly the same view), into 4 narrower beams, which collectively give substantially the original view. 
     The Butler matrix can also operate in “reverse,” assuming that the Butler matrix components (and RF switch, discussed below) can handle the RF power. That is, so far, the system has been shown operating in the receive mode, changing spatial responses to beam responses. However, the system also can operate in reverse or transmit mode, changing beam responses to (wider angle) spatial responses. To operate in the transmit mode, the system would need to be capable of handling RF transmit power, and not destroy or “burn up” the RF components. 
       FIG. 66  shows a simplified view of a PCB (printed circuit board)-mounted system  1300  or “planar switched beam antenna.” Here, M antenna elements  1322  (shown here as square patches, or microstrip antennas) mounted on one surface of a PCB  1325  are used for the input response. It is assumed that all M antenna elements  1322  have a similar azimuth response. Each antenna response, tapped via a coaxial probe, aperture coupling, or other antenna feed mechanism  1323 , is directed to an M-port Butler matrix  1320 , shown as block “B” also mounted on the PCB  1325 . The M-RF beam outputs  1324  from the Butler matrix are fed to an M:1 RF switch  1326  (shown as block “S”) also mounted on the PCB  1325 . The Butler matrix  1320  and RF switch  1326  could be mounted on a separate PCB if desired and in a common housing with the antennas  1322  and PCB  1325 . It is assumed that the final output RF signal, from a given antenna element  1322 , is the stationary response of the system. 
     That is, the RF switch  1326  would be externally controlled, and sequentially switch through each of the beams. Some external system would monitor or qualify each output to determine the optimal or desired one, at which point the RF switch would be controlled to select that respective antenna element  1322 . An RF transceiver or modem  1328  toggles the RF switch  1326 , to each beam, measures the net power output (or other measurement, such as best C/I, or lowest noise, etc.) of each, then selects the beam with the best power (or other measurement, such as best C/I, or lowest noise, etc.). 
     This system, if used in both the transmit and receive modes, assumes that the patch antenna elements  1322 , Butler matrix circuits  1320 , and RF switch  1326 , all have bandwidth covering the entire transmit and receive signal bandwidths. Thus, the system can operate in both directions; converting wide spatial responses into a single selected beam (for receive), and transmitting a signal back towards the desired direction (transmit mode), assuming sufficient bandwidth and transmit power handling capacity, as noted above. 
     The array of antennas  1322  could be formed in the vertical plane, to generate elevation beams, as an alternative to the horizontal array of  FIG. 66 , as discussed below with reference to  FIG. 77 . 
       FIG. 67  shows a simplified top view of the layered structure of one of the patch elements of  FIG. 66 , showing the patch structure  1322 , a ground plane  1342  (above the surface of the PCB  1325 ) with an aperture coupled iris  1344 , and a microstrip transmission line  1323  on the PCB  1325 , carrying the signal. 
       FIG. 68  shows a simplified circuit diagram for the RF switch  1326 . M RF transmission lines  1324  are each connected in parallel, via PIN diodes (or other transistor/solid state switching devices, for RF operational frequencies)  1350 , to a single point. Each PIN diode  1350  is controlled via a control (C) or bias line  1352 ; acting as an electronic switching circuit. While only two control lines  1352  are shown, there are M control lines (C) in total, one for each PIN diode  1350 . The M control lines  1352  can be operated from a single control line (not shown in  FIG. 68 ) by use of a microcontroller (not shown in  FIG. 68 ) or a TTL (binary) logic device (not shown). 
       FIG. 69  shows a block diagram of a system having components as described above with reference to  FIG. 66 . The control input  1352  to the M:1 RF switch  1326  can come from an RF to IF transceiver, or from a modem, determined by the beam selection criteria used. A common housing for the antennas  1322 , Butler matrix  1320  and RF switch  1326 , which may be mounted to one or more PCBs (see  FIG. 66 ) is indicated by reference numeral  1355 . 
       FIG. 70  shows a block diagram similar to  FIG. 69 , but with an RF to IF transceiver (or transverter, as called in MMDS)  1360  added (e.g., mounted on the same PC board  1325 ). The RF circuitry block could include the Butler matrix, the RF switch, and various transceiver components, all on the same PC board as the antenna, or on one or more separate boards, if desired, and in the same housing  1355 . 
       FIG. 71  shows a similar block diagram to  FIG. 70 , but with the modem  1362  added to the system. The modem  1362  would control the M:1 RF switch  1326 , since it would likely have the most flexible capabilities to analyze the various antenna inputs (beams), and determine the optimal beam. All these components may be on one or more PCBs in a common housing  1355 . The output from the modem could connect to a PC or LAN (not shown) via USB cable, ethernet, or LAN cable  1364 . 
       FIG. 72  shows a simplified perspective view of a physical embodiment of a planar system (unit)  1300   a , of  FIG. 71 , with various elements (Butler matrix “B”, RF switch “S”, Transceiver “T”, and Modem “M”) all within the same housing (e.g., a relatively thin rectilinear structure) or on the same PC board  1325 . 
     In the case where it is desirable to separate the transmit and receive systems, or if the transmit and receive bands are too far separated, in frequency, to occupy the same antenna elements (or Butler matrix components, or RF switch components), then they can be broken into two completely separate systems. Such a system  1300   b  is shown in  FIG. 73 , where a set of transmit mode patches  1322 T connects to its own Butler matrix  1320 T and RF switch  1326 T, and similarly, for the receive mode, a set of equivalent antenna elements  1322 R (in this case, shown as patches) tuned to the receive band, a Butler matrix  1320 R and RF switch  1326 R. The system input/output is two RF ports  1370 T and  1370 R. The whole system is contained on a single PC board  1325  and/or within a single housing (i.e., could be on more than one PC board in the housing). 
       FIG. 74  shows a block diagram for the system in  FIG. 73 . There are M receive band antenna elements  1322 R, and N transmit band antenna elements  1322 T. Generally speaking, M can, but does not have to equal N. Additionally, each system has a separate control input  1352 R,  1352 T for the respective RF switch. Indeed, this allows selection of different beams for the transmit and receive bands. This may be the case if a desired signal is to be received from a given direction, but the transmitted signal might be sent out in another direction. 
       FIG. 75  shows the system of  FIG. 74  with the addition of an RF to IF downconverter (or receiver)  1372  for the receive mode, and an IF to RF upconverter (or transmitter/exciter)  1374  for the transmit mode. The system can connect to an external modem (not shown) via coaxial cable(s) or twisted pair transmission line  1376 . The system shown here uses a single cable; which assumes that the transmit and receive band signals are IF diplexed into a signal cable, from the transceivers. 
       FIG. 76  shows the system of  FIG. 75 , and further including an embedded modem  1362 . The modem  1362  can be, but does not have to be, included on the same PCB as either or both the antenna system, and/or transceivers. However, it is assumed that the systems shown in each of  FIGS. 74-76  are contained within respective housings  1355 , i.e., each of these drawings shows a system which is contained in its own housing  1355 . 
       FIG. 77  shows a system  1300   c  similar to that of  FIG. 66 , but using M elevation arrays  1390  of antenna elements  1420  in place of an array of M individual elements. Each column  1390 - 1 ,  1390 - 2 , etc. of antenna elements, which form elevation beams, can be summed, using a parallel or corporate feed, and input to the Butler matrix  1420 . This can similarly be done for the case of summed azimuth elements, i.e., horizontal arrays (not shown), with switched beams in the elevation plane. 
     The systems described thus far may utilize PC board technology (planar and thin), with patch or microstrip antenna elements. By design, a patch element has a real ground plane, and therefore each patch element only “sees” a 180 degree (half hemisphere) view. Thus, the systems shown so far, are generally “one-sided.” An option to obtain full 360 degree coverage is to employ two such systems, back to back, to generate an effective omni-directional system  1300   d , as shown in  FIG. 78 . These can be deployed within the same housing (structure). Each system generates a beam input/output; one for the “front” 0 to 180 degree view, and the other for the “back” 180 to 360 degree (azimuth) view. Thus, the system breaks up the 360 view angle into 2M beams, each with relative beamwidth about 360/2M degrees. Additionally, the two input/output beam ports can be connected to a 2:1 RF switch (with control), not shown, to obtain selection of the final (stationary) beam. However, with this approach, the beams in the endfire direction (towards the edges of the PCB) are highly attenuated (gain), due to the limited view angle for a patch antenna (element). 
     An alternative method to obtain a full 360 degree view angle is to use dipole (etched) antenna elements  1522 , on a PCB  1525 , as shown in  FIG. 79 . Each dipole (shown as “bow-tie” dipole elements, which have broadband characteristics) has a very symmetric azimuth pattern for a full 360 degree coverage. This system does not employ a backplane or ground, as do the patches. Similar to the previous designs, this system uses a Butler matrix  1520  and RF switch  1526 , to generate a single RF input/output port  1570 . However, along the symmetry plane of the printed circuit board (PCB)  1525 , the dipoles  1522  have mirror azimuth beams, as shown in  FIG. 80 . Thus, selection of Beam #1 towards the back, also selects Beam #1 towards the front. In the example shown in  FIG. 80 , there are only 4 states to choose from, and switch  1526  selects two beams, in summation; one from each side of the symmetry plane. 
       FIG. 81  shows a typical installation, either in a home or office, with an antenna system  1300  in accordance with any of the embodiments described above located on a wall, with a cable run  1302  down the wall, to a PC or server  1304 . 
       FIGS. 82 and 83  show an antenna unit  1400 , alone, and installed to a laptop computer  1402 . Wireless internet systems require large bandwidths and data rates (over 50 kbps, up to 2000 kbps), much higher than conventional wireless voice systems (9.8 kbs). To achieve these rates requires much higher system gain levels. These gains can only be obtained by either reducing the distance from the base station (or picocell) to the remote (CPE unit, terminal unit) or by increasing the directive gains of the base station antenna and/or terminal equipment antenna. Antenna gain is a function of the physical size of the antenna. Aesthetics and zoning issues limits increasing the size of the base station antenna (to achieve additional directive gain). Thus, one alternative is to increase the gain of the terminal equipment antenna, which means increasing its physical size. Currently wireless voice systems (on a handset) use 2″ stub (monopole) omni-directional antennas, with at best 0 dBi of gain. To satisfy the higher data rates, requires additional gain of at least 10 dB (20 dB desired). 
     The RF Switched Beam Planar Antenna described above is a good approach for this requirement, and is cost effective. This application would embed the RF electronics within the antenna  1400 , and mount the system to the laptop unit. The switched beams would continually search for the best multipath signal, and lock on; transporting this signal to the modem. The envelop of the beams is within an ellipse; with the major axis of the ellipse in the directions perpendicular to the faces of the antenna system. Thus, the side (endfire) angles of the system would have much lower (reduced) gain. A series of LEDS  1404  or other suitable display elements could be used (shown at the top), which could aid the user to help orient the unit, to more optimally orient the antenna faces towards directions of greater signal power. 
     The flat panel antenna  1400  may further have a USB or other suitable connection  1406  to interface with the laptop computer  1402 . The cable or other connector  1406  may also include a power cable to use battery or other power from the laptop computer  1402 , or alternatively, on-board battery power may be included within the flat panel antenna unit  1400 . If desired, the battery used may be a solar powered type of battery. 
     In the illustrated embodiment, the flat panel antenna  1400  has a generally L-shaped cross-sectional profile such that the LEDs  1404  or other display elements are readily visible over the top of the laptop computer  1402  when the antenna  1400  is installed thereupon, as indicated in  FIG. 83 . However, other shapes of the panel  1400  and other configurations and locations of LEDs or other display elements may be utilized without departing from the invention. 
     The flat panel antenna unit  1400  may be coupled with the case or housing of the laptop computer  1402  by using one or more velcro pads  1408 , or “sticky” tape, or the like. Other arrangements of snap-on, snap-off fasteners or other mounting parts or mounting hardware may be utilized without departing from the invention. 
     The LEDs or other display elements  1404 , as well as suitable circuitry for determining signal strength, or some other desirable measure of signal quality may be incorporated in the flat panel antenna  1400 , or indeed in any antenna configured in accordance with the invention. 
     Certain of the flat antennas described above may have azimuth and/or elevation beamwidths of 90.degree. or less, which can restrict or reduce coverage in the end-fire directions. To achieve wider angle coverage, multiple antennas may be used on one or both sides of the flat-panel repeater. One such embodiment is illustrated in  FIG. 84 , where a repeater  1500  has a single base-station-facing antenna  1501 , and three mobile-facing antennas  1502 ,  1503  and  1504 . The plane of the middle antenna  1503  is parallel to that of the base-station-facing antenna  1501 , but the planes of the other two antennas  1502  and  1504  intersect the planes of antennas  1501  and  1503  at angles of about 45.degree. so as to produce beams that overlap the beam of the middle antenna  1503 , as illustrated by the broken lines in  FIG. 84 . The azimuth beamwidth of the middle antenna  1503  is typically only about 80.degree., but the addition of the two angled antennas  1502  and  1504  provides wide angle coverage on the mobile side of the repeater.  FIG. 85  illustrates how an RF splitter  1505  can be used to connect all three mobile-facing antennas  1502 - 1504  to the same diplexer  1506 . It will be understood that the same arrangement illustrated in  FIGS. 84 and 85  can also be used to provide wide-angle elevation coverage by simply rotating the structure 90.degree. so that  FIG. 84  becomes a side elevation rather than a top plan view. 
       FIG. 86  illustrates an alternative technique for achieving wide-angle azimuth coverage by using a dipole  1510  as the mobile-facing antenna, with the adjacent surface  1511  of the flat-panel repeater  1512  serving as a flat reflector. The combination of the dipole  1510  and the reflector  1511  produces a wide-angle azimuth beamwidth.  FIG. 87  illustrates a modified repeater  1513  which forms a shaped (concave) reflector  1514  on the mobile-facing side to further increase the azimuth beamwidth. 
     The antennas on opposite sides of the flat-panel repeater may also be mounted in planes that are not parallel to each other to reach the desired coverage areas. For example,  FIG. 88  illustrates a repeater  1520  having a mobile-facing antenna  1521  lying in a plane that intersects the plane of the base-station-facing antenna  1522  at an angle .theta. to service a mobile coverage area located in the direction of the beam axis  1523  of the antenna  1521 . 
     The repeater may also be designed to re-transmit signals in a direction orthogonal to the direction in which the signals are received by the repeater. The orthogonal relationship of the two paths may be in azimuth, in elevation, or a combination of the two. For example,  FIG. 89  illustrates a repeater  1530  designed to receive horizontally propagating signals and re-transmit them vertically downward. Such a repeater is useful, for example, when the repeater must be located above the intended coverage area, or where the signal-to-noise ration is best at a location higher than the intended coverage area. In the illustrative embodiment of  FIG. 89 , base station signals propagated along a horizontal path are received by a vertically polarized monopole (or dipole)  1531  extending upwardly from one side (top) of the flat-panel repeater  1530 , and then re-transmitted vertically downward by a flat, horizontally polarized antenna  1532  on the opposite side (bottom) of the repeater. A ground plane  1533  for the antenna  1532  is provided on the lower surface of the repeater body which contains the electronics. The polarization difference between the two antennas  1531  and  1532  improves the isolation between the two antennas. 
     Referring next to  FIG. 90 , there is shown an antenna system for re-transmitting a GPS signal  1409  inside a structure  5 . The antenna system includes a link antenna  1412  for receiving the GPS signal  1409  from a GPS transmitting antenna  1411 , a GPS repeater  1414  for amplifying the received GPS signal  1410  to produce a second GPS signal  1415  and a broadcast antenna  1416  for re-transmitting the second GPS signal  1415  inside the structure  5 . This embodiment works best where the structure  5  has the dimensions of a two-story building. 
     The GPS repeater  1414  feeds the received GPS signal  1410  into the structure  5 . In one embodiment, the external link antenna  1412  captures the GPS signal  1409  and feeds it to the GPS repeater  1414 . The GPS repeater  1414  boosts the received GPS signal  1410  and drives an internal broadcast antenna  1416  that radiates the second GPS signal  1415  inside the structure  5 . 
     The present invention overcomes the inability of GPS receivers to work inside a structure, which is a major shortcoming of the Global Positioning System. As the GPS is used in more commercial applications, the ability to overcome this shortcoming becomes very important. Examples of commercial uses of the GPS include: Enhanced 911 service; wireless phone services that provide an Internet connection; wireless services that provide the location of, e.g., hotels, restaurants, and businesses; services that provide assistance to the elderly and handicapped; and locator services (provide by, e.g., rental car companies) that provide location information that can be received inside structures such as parking garages, buildings and tunnels. 
     In one embodiment, the GPS repeater  1414  includes the components shown in  FIG. 92 . Those components include a band pass filter  1418 , a low noise amplifier  1420 , a gain block  1422 , a power amp  1424  and second band pass filter  1426 . The band pass filters  1418  and  1426  are selected so as to reduce the out-of-band signals. For a GPS repeater system, the pass band will usually be around 1575.42 MHz (+/−500 kHz). In one embodiment, the gain block  1422  includes a radio frequency (RF) amplifier  1428 , a band pass filter  1430  and a second RF amplifier  1432 , as shown in  FIG. 93 . 
     In another embodiment shown in  FIG. 94 , the gain block  1422  includes a mixer  1434  for down converting the GPS signal  1410  to an intermediate frequency (IF) signal  1436 . The GPS signal  1410  is combined by a mixer  1434  with a local oscillator (LO) signal  1440  to produce the IF signal  1436 . In one embodiment, the IF is between about 140 MHz to 160 MHz, depending on the application. Thus, where the LO signal  1440  is 1640 MHz and the GPS signal  1410  is 1.5 GHz, then the IF signal would be 140 MHz. The IF signal  1436  is amplified by amplifiers  1442  and filtered by a band pass filter  1444 . The band pass filter  1444  significantly reduces the complex components or images of the GPS signal  1410  and the LO signal  1440 . A second mixer  1446  converts the IF signal  1436  to produce the RF signal  1438 . The IF signal  1436  is combined by the second mixer  1446  with the LO signal  1440  to produce the RF signal  1438 . In one embodiment, the IF is between about 140 MHz to 160 MHz, depending on the application. Thus, where the LO signal  1440  is 1640 MHz and the IF signal is 140 MHz, then the RF signal  1438  is 1.5 GHz. Therefore, in this embodiment, the RF signal  1438  is the second GPS signal  1415 . 
     In one embodiment, the RF signal  1438  is an unlicensed frequency signal. The unlicensed frequency signal can be in any frequency range not licensed by the Federal Communications Commission (FCC). Some examples of unlicensed frequency bands include: 902-928 MHz and 2.4 GHz. 
     Referring to  FIG. 91 , there is shown an antenna system  1540  for re-transmitting a received GPS signal  1541  inside a structure  1542 . The antenna system  1540  includes a link antenna  1543  for receiving the GPS signal  1541 , a primary GPS repeater  1545  for amplifying the GPS signal  1541  to produce an RF signal  1538 , a first broadcast antenna  1547  to broadcast the RF signal  1538  to one or more secondary repeaters  1650  located to cover the intended coverage area inside the structure  1542 . The RF signal  1538  is broadcast to the secondary repeater(s)  1650  at either the original GPS frequency or another available frequency. In one embodiment, the RF signal  1538  is in one of the unlicensed frequency bands such as the Instrumentation, Scientific and Medical (ISM) frequency band of 902 MHz-928 MHz. Each secondary repeater  1650  receives the RE signal  1538  via a link antenna  1544 , amplifies the RF signal  1538  to produce a second GPS signal  1546  and re-transmits the second GPS signal  1546  via a second broadcast antenna  1548  inside the structure  1542 . The secondary repeater(s)  1650  may be placed inside the structure  1542  or even placed external to the structure  1542  such that the RF signal  1538  can be re-transmitted into the structure through the windows or walls of the structure. This embodiment works best where the structure  1542  has the dimensions of a multi-story building. 
     In one embodiment, the primary repeater  1545  includes the components shown in  FIG. 95 . Those components include a band pass filter  1549 , a low noise amplifier  1550 , a gain block  1551 , a power amp  1552  and second band pass filter  1553 . In one embodiment, the gain block  1551  includes, as shown in  FIG. 96 , a mixer  1555  for down converting the GPS signal  1541  to an IF signal  1557 . The GPS signal  1541  is combined by a mixer  1555  with a local oscillator (LO) signal  1554  to produce the IF signal  1557 . In one embodiment, the IF is between about 140 MHz to 160 MHz, depending on the application. Thus, where the LO signal  1540  is 1640 MHz and the GPS signal  1541  is 1.5 GHz, then the IF signal would be 140 MHz. The IF signal  1557  is amplified by amplifiers  1556  and filtered by a band pass filter  1562 . The band pass filter  1562  significantly reduces the complex components or images of the GPS signal  1541  and the LO signal  1554 . A second mixer  1558  up converts the IF signal  1554  to produce the RF signal  1538 . The IF signal  1554  is combined by the second mixer  1558  with a second LO signal  1564  to produce the RF signal  1538 . In one embodiment, the IF is between about 140 MHz to 160 MHz, depending on the application. Thus, where the second LO signal  164  is 762 MHz and the IF signal is 140 MHz, then the RF signal  1538  is 902 MHz. 
     In one embodiment, the secondary repeater  1650  includes the components shown in  FIG. 97 . Those components include a band pass filter  1618 , a low noise amplifier  1620 , a gain block  1622 , a power amp  1624  and second band pass filter  1626 . In one embodiment, the gain block  1622  includes, as shown in  FIG. 98 , a mixer  1670  for down converting the RF signal  1538  to an IF signal  1672 . The RF signal  1538  is combined by a mixer  1670  with a local oscillator (LO) signal  1678  to produce the IF signal  1672 . In one embodiment, the IF is between about 140 MHz to 160 MHz, depending on the application. Thus, where the LO signal  1540  is 742 MHz and the RF signal  1538  is 902 MHz, then the IF signal would be 160 MHz. The IF signal  1672  is amplified by amplifiers  1674  and filtered by a band pass filter  1676 . The band pass filter  1676  significantly reduces the complex components or images of the RF signal  1538  and the first LO signal  1678 . A second mixer  1680  converts the IF signal  1672  to produce the second GPS signal  1615 . The IF signal  1672  is combined by the second mixer  1680  with a second LO signal  1682  to produce the second GPS signal  1615 . In one embodiment, the IF is between about 140 MHz to 160 MHz, depending on the application. Thus, where the second LO signal  1682  is 1340 MHz and the IF signal is 160 MHz, then the second GPS signal  1615  is 1.5 GHz. 
     Thus, the GPS repeater system of the present invention fills the GPS null or “blank” areas within structures. In this way, the GPS can be used to locate individuals inside buildings, tunnels, garages, etc. 
     In another embodiment, the repeater system of the present invention is used in satellite transmission applications such as digital radio. Like GPS applications, digital radio signals transmitted by satellites can be obstructed from receiving antennas by structures such as buildings, car garages, tunnels, etc. Therefore, the claimed repeater is capable of re-transmitting a satellite signal inside a structure such that an uninterrupted satellite signal can be transmitted to a receiver. 
     While the present invention has been illustrated by a description of one or more embodiments thereof and while these embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.