Patent Publication Number: US-6703976-B2

Title: Scaleable antenna array architecture using standard radiating subarrays and amplifying/beamforming assemblies

Description:
FIELD OF THE INVENTION 
     The present invention relates to a scaleable modular antenna array that uses standard subarrays and circuit assemblies. 
     BACKGROUND OF THE INVENTION 
     Satellite communications have become an important component in worldwide telecommunications. As the demand for satellite communications increases, the need for communications satellites that are less expensive and quicker to develop also increases. One approach to providing such communications satellites is described in U.S. Pat. No. 5,666,128 to Murray et al., which describes an array antenna especially adapted for spacecraft use that includes a support frame made up of intersecting beams which form an “eggcrate” of square openings and a plurality of subarrays or radiating tiles that are dimensioned to fit within the openings. There are limitations to this approach as applied to millimeter wave frequencies. One limitation is that the gaps between the radiating tiles become too large, in wavelengths at the frequency of interest, to achieve acceptable beam quality. The gaps between tiles are required to provide space for the support frame. Another limitation is based on the fact that, for a given coverage area, the quantity of phase shifters per radiating tile per radiated or received beam is proportional to the square of the frequency. At millimeter wave frequencies (˜30 GHz), there is inadequate space in a tile to package the components required to create the number of radiated or received beams that are desired in many applications. 
     What is needed is a phased array antenna design that is modular and scaleable in terms of beam quantity, coverage area, and receive sensitivity/transmit effective isotropic radiated power (EIRP), which permits the design to be tailored to specific applications relatively inexpensively, quickly, and with low development risk. 
     SUMMARY OF THE INVENTION 
     The present invention is a phased array antenna design that is modular and scaleable in terms of beam quantity, coverage area, and receive sensitivity/transmit EIRP, which permits the design to be tailored to specific applications relatively inexpensively, quickly, and with low development risk. This invention can be applied to both transmit and receive phased array antenna applications. 
     In one embodiment of the present invention, a modular array building block for an antenna array comprises: a plurality of antenna elements, each antenna element operable to receive and output an electromagnetic wave signal, the antenna elements arranged adjacent to each other, a plurality of antenna element interface assemblies; each antenna element interface assembly coupled to one of the plurality of antenna elements and coupling the received signal to an amplifier, and a plurality of circuit board assemblies, the circuit board assemblies arranged substantially parallel to each other, each circuit board assembly comprising: a plurality of amplifiers, each amplifier operable to amplify a received signal from an antenna element, and a plurality of beamformers, each beamformer coupled to an output of an amplifier, wherein the circuit board assemblies, antenna element interface assemblies and antenna elements are arranged so as to form a module. 
     In one aspect of the present invention, the antenna elements are arranged adjacent to each other so as to form a grid pattern, such as a triangular grid pattern or a rectangular grid pattern. 
     In one aspect of the present invention, at least some of the circuit boards are populated with fewer amplifiers and beamformers than could be accommodated. 
     In one aspect of the present invention, the antenna elements are arranged so as to form a plurality of rows and the antenna elements and antenna element interfaces are oriented oppositely in adjacent rows. The circuit boards may have non-uniform spacing within the module. The antenna element interface assemblies may comprise waveguide assemblies. 
     In one aspect of the present invention, the antenna elements are arranged so as to form a plurality of rows and the antennas and antenna element interface assemblies are oriented similarly in adjacent rows. The circuit boards may have uniform spacing within the module. The antenna element interface assemblies may comprise waveguide assemblies. 
     In one aspect of the present invention, each antenna element interface assembly comprises a waveguide assembly. Each waveguide assembly may further comprise a waveguide filter. Each waveguide assembly further may comprise a signal probe operable to convert an electromagnetic wave signal from the antenna to a corresponding electrical signal and output the electrical signal to the amplifier. 
     In one aspect of the present invention, the module comprises larger antenna elements and a correspondingly smaller number of circuit board assemblies, larger antenna elements and correspondingly less populated circuit board assemblies, larger antenna elements and a correspondingly smaller number of less populated circuit board assemblies, smaller antenna elements and a correspondingly larger number of circuit board assemblies, smaller antenna elements and correspondingly more populated circuit board assemblies, or smaller antenna elements and a correspondingly larger number of more populated circuit board assemblies. 
     In one aspect of the present invention, the beamformers are radio frequency beamformers. 
     In one aspect of the present invention, the beamformers are intermediate frequency beamformers. 
     In one aspect of the present invention, connections between the plurality of amplifiers and the plurality of beamformers are interleaved so that if a number of amplifiers are omitted from a circuit board assembly, at least one beamformer can be omitted from the circuit board assembly 
     In one embodiment of the present invention, a modular array building block for an antenna array comprises: a plurality of antenna elements, each antenna element operable to transmit an electromagnetic wave signal, the antenna elements arranged adjacent to each other, a plurality of antenna element interface assemblies; each antenna element interface assembly coupled to one of the plurality of antenna elements and coupling the signal from an amplifier, and a plurality of circuit board assemblies, the circuit board assemblies arranged substantially parallel to each other, each circuit board assembly comprising: a plurality of amplifiers, each amplifier operable to amplify a signal coupled to an antenna element, and a plurality of beamformers, each beamformer coupled to an input to an amplifier, wherein the circuit board assemblies, antenna element interface assemblies and antenna elements are arranged so as to form a module. 
     In one embodiment of the present invention, an antenna array comprises: a plurality of antenna array modules interlocking so as to form a contiguous antenna array structure, wherein each antenna array module comprises: a plurality of antenna elements, each antenna element operable to receive and output an electromagnetic wave signal, the antenna elements arranged adjacent to each other, a plurality of antenna element interface assemblies; each antenna element interface assembly coupled to one of the plurality of antennas and coupling the received signal to an amplifier; and a plurality of circuit board assemblies, the circuit board assemblies arranged substantially parallel to each other, each circuit board assembly comprising: a plurality of amplifiers, each amplifier operable to amplify a received signal from an antenna element, and a plurality of beamformers, each beamformer coupled to an output of an amplifier, wherein the circuit board assemblies, antenna element interface assemblies and antenna elements are arranged so as to form a module. Signal frequency, control, and DC power harnesses are used to electrically connect the antenna array modules to form an antenna array. The signal frequency selected for beamforming and power combining may either be the radio frequency (RF) or an intermediate frequency (IF) frequency. 
     In one embodiment of the present invention, an antenna array comprises: a plurality of antenna array modules interlocking so as to form a contiguous antenna array structure, wherein each antenna array module comprises: a plurality of antenna elements, each antenna element operable to transmit an electromagnetic wave signal, the antenna elements arranged adjacent to each other, a plurality of antenna element interface assemblies; each antenna element interface assembly coupled to one of the plurality of antennas and coupling the signal from an amplifier, and a plurality of circuit board assemblies, the circuit board assemblies arranged substantially parallel to each other, each circuit board assembly comprising: a plurality of amplifiers, each amplifier operable to amplify a signal coupled to an antenna element, and a plurality of beamformers, each beamformer coupled to an input to an amplifier, wherein the circuit board assemblies, antenna element interface assemblies and antenna elements are arranged so as to form a module. Signal frequency, control, and DC power harnesses are used to electrically connect the antenna array modules to form an antenna array. The signal frequency selected for beamforming and power dividing may either be the RF frequency or an IF frequency. 
     In one embodiment of the present invention, an antenna array comprises: a plurality of antenna array modules interlocking so as to form a contiguous antenna array structure, wherein each antenna array module comprises: a plurality of antenna elements, each antenna element operable to receive and output an electromagnetic wave signal and to transmit an electromagnetic wave signal, the antenna elements arranged adjacent to each other; a plurality of antenna element interface assemblies, each antenna element interface assembly coupled to one of the plurality of antenna elements and coupling the received signal to a receive amplifier and coupling the signal to be transmitted from a transmit amplifier; and a plurality of circuit board assemblies, the circuit board assemblies arranged substantially parallel to each other, each circuit board assembly comprising: a plurality of receive amplifiers, each receive amplifier operable to amplify a received signal from an antenna element, a plurality of transmit amplifiers, each amplifier operable to amplify a signal coupled to an antenna element, a plurality of beamformers, each beamformer coupled to an input to a transmit amplifier and coupled to an output of a receive amplifier, a plurality of duplexing devices coupling a transmit amplifier output and a receive amplifier input to an antenna element interface assembly, a plurality of duplexing devices coupling each beamformer to a transmit amplifier input and to a receive amplifier output; wherein the circuit board assemblies, antenna element interface assemblies and antenna elements are arranged so as to form a module; and signal frequency, control, and DC power harnesses to electrically connect the plurality of antenna array modules so as to form the antenna array. The signal frequency selected for beamforming and power dividing/combining may either be the RF frequency or an IF frequency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details of the present invention, both as to its structure and operation, can best be understood by referring to the accompanying drawings, in which like reference numbers and designations refer to like elements. 
     FIG. 1 is a schematic diagram of a circuit of a phased array receiving system, according to the present invention. 
     FIG. 2 is a block diagram of an embodiment of an amplifier/beamformer matrix module board used in a phased array receiving system, according to the present invention. 
     FIG. 3 is a block diagram showing an example of a plurality of amplifier/beamformer matrix module boards, shown in FIG. 2, combined to form a phased array receiving system. 
     FIG. 4 is a block diagram showing an example of a plurality of amplifier/beamformer matrix module boards, shown in FIG. 2, combined to form a phased array receiving system. 
     FIG. 5 is an example of the physical arrangement of amplifier/BFMM boards that form an array module. 
     FIG. 6 is a block diagram of an antenna element assembly. 
     FIGS. 7 a ,  7   b ,  7   c ,  7   d ,  7   e ,  7   f ,  7   g ,  7   h , and  7   i  are diagrams of examples of antenna element configurations. 
     FIG. 8 is a table summarizing a number of exemplary arrangements of array modules. 
     FIGS. 9 a ,  9   b ,  9   c , and  9   d  is are diagrams showing a number of views of an exemplary antenna element. 
     FIGS. 10,  11 , and  12  are diagrams showing a number of exemplary antenna element assemblies. 
     FIG. 13 shows a partially built-out circuit board assembly, which is included in the present invention 
     FIG. 14 shows the circuit board assembly shown in FIG. 13, along with additional installed components. 
     FIG. 15 shows two circuit board assemblies, each similar to the circuit board assembly shown in FIG.  14 . 
     FIG. 16 shows the circuit board assemblies shown in FIG. 15, along with additional components. 
     FIG. 17 shows a partially built-out antenna array module, according to the present invention. 
     FIG. 18 shows an antenna array module shown in FIG. 17, populated with all circuit board assemblies, waveguide assemblies, and antenna elements. 
     FIG. 19 shows a rear view of the antenna array module shown in FIG. 18 with some additional components. 
     FIG. 20 shows a rear view of the antenna array module shown in FIG. 19, along with additional components. 
     FIG. 21 is a front view of a complete antenna array, according to the present invention. 
     FIG. 22 is an exemplary block diagram of electrical connections between the antenna array modules that are contained in a complete antenna array. 
     FIG. 23 is a schematic diagram of a circuit of a phased array transmitting system, according to the present invention. 
     FIG. 24 is a schematic diagram of a circuit of a phased array transmit/receive system, according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a phased array antenna design that is modular and scaleable in terms of beam quantity, coverage area, and receive sensitivity/transmit EIRP, which permits the design to be tailored to specific applications relatively inexpensively, quickly, and with low development risk. 
     A schematic diagram of a circuit  100  of a phased array receiving system, according to the present invention, is shown in FIG.  1 . System  100  includes a plurality of antenna element assemblies  102 A- 102 N, a plurality of low noise  104 A- 104 N, a plurality of beamformers  106 A- 106 N, a plurality of power combiners  108 A- 108 M, and a plurality of beam ports  110 A- 110 M. For clarity of description, the number of antenna element assemblies is designated as “n”. Antenna element assemblies  102 A- 102 N are arranged to form a two dimensional antenna array. Each antenna element assembly, such as antenna element assembly  102 A, receives a radio frequency (RF) electromagnetic wave signal and converts it to a corresponding electrical signal, which is output from the antenna element assembly to a low noise amplifier. Typically, an antenna element assembly includes a receiving antenna element, such as a horn or waveguide slot antenna element, one or more waveguides, filters, signal probes, etc. The input of each low noise amplifier (LNA) is connected to the output of one antenna element assembly. Thus, if there are n antenna element assemblies, there are n LNAs as well. The LNA receives the electrical signal output from the connected antenna element assembly and amplifies the electrical signal. For example, the input of LNA  104 A is connected to the output of antenna element assembly  102 A and LNA  104 A receives and amplifies the electrical signal output from antenna element assembly  102 A. 
     In a preferred embodiment, waveguides are used to interface antenna elements to the remaining circuitry. However, it is to be noted that a waveguide is merely one example of an antenna element interface assembly. Other examples may include coaxial cable assemblies or fiber optic assemblies. Although, in this specification, waveguides are used as examples of antenna element interface assemblies, the present invention contemplates any and all embodiments of antenna element interface assemblies. 
     The output of each LNA is connected to the input of a beamformer. Thus, there are n beamformers. For example, the output of LNA  104 A is connected to the input of beamformer  106 A. Each beamformer includes a power divider and a plurality of phase shifters. For example, beamformer  106 A includes power divider  112  and phase shifters  114 A- 114 M. Power divider  112  divides the signal input to beamformer  106 A into a plurality of signals of nominally equal power, which are output from the plurality of outputs of power divider  112 . For clarity of description, the number of signals into which power divider  112  divides the input signal, which is equal to the number of outputs from power divider  112  and to the number of phase shifters in the beamformer, is designated “m”. As power divider  112  has one input and m outputs, it may be designated a “ 1 :m” power divider. 
     Each output of power divider  112  is connected to the input of a corresponding phase shifter  114 A- 114 M. Each phase shifter shifts its input signal by a predetermined phase angle, which may be different for each phase shifter in a given beamformer. Each beamformer has a plurality of outputs, each output being an output from one of the phase shifters included in the beamformer. For example, beamformer  106 A has a plurality of outputs, each output being an output from a phase shifter  114 A-M. As there are n beamformers  106 A- 106 N and each beamformer has m outputs, the total number of outputs from all beamformers is n * m. 
     Each output of a beamformer  106 A- 106 N is connected to an input of a power combiner  108 A- 108 M. Each power combiner has n inputs, which is equal to the number of antenna element assemblies, LNAs, and beamformers. 
     Thus, each power combiner  108 A- 108 M may be designated an “n:l” power combiner. There are m power combiners, which is equal to the number of phase shifters in each beamformer  106 A- 106 N. Each input of each power combiner  108 A- 108 M is connected to the output of one phase shifter from each beamformer  106 A- 106 N. Each power combiner combines the input signals to form a single output signal. As there are m power combiners  108 A- 108 M, there are m signals output from power combiners  108 A- 108 M. The outputs from power combiners  108 A- 108 M are beam ports  110 A- 110 M. 
     The phase shifters are used to electronically steer the beams created by the antenna array. A beam may be pointed in different directions by resetting the phase shifts of all of the phase shifters associated with that beam. 
     A block diagram of a preferred embodiment of an amplifier/beamformer matrix module board  200  used in a phased array receiving system, according to the present invention, is shown in FIG.  2 . Board  200  includes a plurality of low noise amplifiers (LNAs)  202 A- 202 H, power dividers  204 A- 204 H, beamformer matrix modules (BFMM)  206 A,  206 B,  206 C, and  206 D, power combiners  208 A- 208 P and  210 A- 210 P, and beam ports  212 A- 212 P and  214 A- 214 P. Each BFMM has four input ports. Each input port connects to a 1:16 power divider, which, in turn, connects to 64 phase control circuits. The phase control circuits are connected through 16 4:1 power combiners to 16 output ports. 
     Each LNA  202 A- 202 H is connected to the output of an antenna element assembly (not shown). In the preferred embodiment shown in FIG. 2, there are provisions for eight LNAs on each board  200 . The output from each LNA  202 A- 202 H is connected to a power divider. For example, the output of LNA  202 A is connected to the input of power divider  204 A. As there are provisions for eight LNAs  202 A- 202 H, there are likewise provisions for eight power dividers  204 A- 204 H. 
     In the preferred embodiment shown in FIG. 2, each power divider  204 A- 204 H is a 2:1 power divider. That is, each power divider  204 A- 204 H has one input and two outputs. Each output of each power divider  204 A- 204 H is connected to an input of a BFMM. For example, one output of power divider  204 A is connected to an input of BFMM  206 A and the other output of power divider  204 A is connected to an input of BFMM  206 C (connection shown as a dashed line). The connections of the outputs of power dividers associated with LNAs to inputs of BFMMs are interleaved. That is, the outputs of power dividers connected to adjacent LNAs are connected to inputs of alternate sets of BFMMs. Thus, the outputs of power divider  204 A, which is connected to LNA  202 A, are connected to inputs to the set of BFMMs including BFMM  206 A and BFMM  204 C, while the outputs power divider  204 B, which is connected to adjacent LNA  202 B, are connected to inputs to the set of BFMMs including BFMM  206 B and BFMM  206 D. As a result, each BFMM is coupled to alternate LNAs. 
     The outputs from each BFMM  206 A- 206 D are connected to inputs of power combiners. In the preferred embodiment shown in FIG. 2, each BFMM  206 A- 206 D has sixteen outputs and each power combiner  208 A- 208 P and  210 A- 210 P is a 2:1 combiner and has two inputs and one output. The inputs of the power combiners are interleaved between the BFMMs. For example, one input of power combiner  208 A is connected to an output from BFMM  206 A, which is in the set of BFMMs including BFMM  206 A and BFMM  204 C, and the other output of power combiner  208 A is connected to an output from BFMM  206 B, which is in the set of BFMMs including BFMM  206 B and BFMM  206 D. Likewise, one input of power combiner  210 A is connected to an output from BFMM  206 C, which is in the set of BFMMs including BFMM  206 A and BFMM  204 C, and the other output of power combiner  210 A is connected to an output from BFMM  206 D, which is in the set of BFMMs including BFMM  206 B and BFMM  206 D. The outputs of the power combiners  208 A- 208 P and  210 A- 210 P form beamports  212 A- 212 P and  214 A- 214 P. 
     A plurality of amplifier/beamformer matrix module boards  200 , shown in FIG. 2, are combined to form a phased array receiving system, such as phased array receiving system  300 , shown in FIG.  3 . As shown in FIG. 3, a plurality of amplifer/BFMM boards, such as boards  302 A- 302 X are arranged in an array module, such as array module  304 A. A plurality of array modules, such as array modules  304 A- 304 Y are arranged to from the phased array receiving system. 
     The outputs from the plurality of amplifer/BFMM boards  302 A- 302 X, which are beamports, such as beamports  212 A- 212 P and  214 A- 214 P, shown in FIG. 2, are connected to a plurality of power combiners, such as power combiners  306 A-A through  306 A-M. For example, outputs from amplifer/BFMM boards  302 A- 302 X are connected to the inputs to power combiner  306 A-A, while different outputs from amplifer/BFMM boards  302 A- 302 X are connected to the inputs to power combiner  306 A-B, etc. The outputs from the power combiners of each array module, such as modules  304 A- 304 Y, are connected to the inputs to a plurality of power combiners, such as power combiners  308 A- 308 M. For example, the outputs of power combiners  306 A-A through  306 Y-A are connected to inputs of power combiner  308 A. Likewise, the outputs of power combiners  306 A-M through  306 Y-M are connected to inputs of power combiner  308 M. The outputs from power combiners  308 A- 308 M are the beam outputs from the phased array receiving system. 
     The exemplary system shown in FIG. 3 is arranged to provide a scan coverage of ±8.7° (elevation)×±8.7° (azimuth), which would be suitable for global coverage for a Geostationary communications satellite. In this example, the antenna elements that are connected to the amplifier/BFMM boards are 1×1 antenna elements, which provide the scan coverage of ±8.7°×±8.7°. As shown in FIG. 2, in a preferred embodiment, there are provisions for up to eight antenna elements to be connected to an amplifier/BFMM board. In the example shown in FIG. 3, there are eight antenna elements connected to each amplifier/BFMM board and there are eight amplifier/BFMM boards in each array module  304 A  304 Y. Thus, there are 64 antenna elements in each array module  304 X- 304 Y. As there are eight amplifier/BFMM boards in each array module, each power combiner, such as power combiner  306 A-A, is an 8:1 power combiner having eight inputs. Each input is connected to a different amplifier/BFMM board. 
     The number of array modules in the phased array receiving system is dependent upon engineering factors, such as the size and weight capacity of the satellite platform, the available power, the necessary antenna gain, etc., and upon cost factors. The necessary antenna gain determines the number of antenna elements that are required. In the example shown in FIG. 3, the total number of antenna elements is designated “n”. As there are 64 antenna elements per array module, the number of array modules is n/64. The amplifier/BFMM boards in each array module each have a number of outputs designated “m”. There are then m outputs from each array module and m power combiners  308 A- 308 M. Each power combiner, such as power combiner  308 A, has one input per array module, or n/64 inputs and is an n/64:1 power combiner. The phased array receiving system thus has m beam outputs. 
     An example of a phased array receiving system that is arranged to provide a scan coverage of ±4°×±4°. As shown in FIG.  4 . This scan range covers nearly one quarter of the surface of the earth, as seen by a geostationary communications satellite. In this example, the antenna elements that are connected to the amplifier/BFMM boards are 2×2 antenna elements, which provide the scan coverage of ±4°×±4°. As shown in FIG. 2, in a preferred embodiment, there are provisions for up to eight antenna elements to be connected to an amplifier/BFMM board. In the example shown in FIG. 4, there are four antenna elements connected to each amplifier/BFMM board and there are four amplifier/BFMM boards in each array module  304 A- 304 Y. In comparison to the configuration shown in FIG. 3, four complete amplifier/BFMM boards are omitted. Also, the four remaining amplifier/BFMM boards are only populated with four LNAs ( 202 A,  202 C,  202 E, and  202 G) and two BFMMs ( 206 A and  206 C). Four LNAs ( 202 B,  202 D,  202 F, and  202 H) and two BFMMs ( 206 B and  206 D) are omitted. These changes result in a substantial reduction in mass, power consumption, and cost and can be achieved without redesigning the amplifier/BFMM board. There are 16 antenna elements in each array module  304 A- 304 Y. As there are four amplifier/BFMM boards in each array module, each power combiner, such as power combiner  306 A-A, is a 4:1 power combiner having four inputs. Each input is connected to a different amplifier/BFMM board. 
     The number of array modules in the phased array receiving system is dependent upon engineering factors, such as the size and weight capacity of the satellite platform, the available power, the necessary antenna gain, etc., and upon cost factors. The necessary antenna gain determines the number of antenna elements that are required. In the example shown in FIG. 4, the total number of antenna elements is designated “n”. As there are 16 antenna elements per array module, the number of array modules is n/16. The amplifier/BFMM boards in each array module each have a number of outputs designated “m”. There are then m outputs from each array module and m power combiners  308 A- 308 M. Each power combiner, such as power combiner  308 A, has one input per array module, or n/16 inputs and is an n/16:1 power combiner. The phased array receiving system thus has m beam outputs. 
     An example of the physical arrangement of amplifier/BFMM boards that form an array module is shown in FIG.  5 . In this example, eight amplifier/BFMM boards are arranged to form an array module. Each amplifier/BFMM boards has eight LNAs and generates 32 beams per board. Each LNA is connected to one antenna element, so there are eight antenna elements connected to each board, for total of 64 antenna elements. 
     A block diagram of an exemplary antenna element assembly  102 , shown in FIG. 1, is shown in FIG.  6 . In this example, the antenna element is a horn radiator antenna structure. However, the present invention contemplates slot radiator antenna structures as well. Antenna element assembly  102  includes an antenna element  602  and waveguide assembly  603 . Waveguide assembly  603  includes waveguide portion  604 , waveguide filter  606 , and signal probe  608 . Antenna element  602  receives radio frequency (RF) electromagnetic wave signals and directs the signals to waveguide  604 . Waveguide portion  604  channels the signals to waveguide filter  606 . Waveguide filter  606  is a bandpass filter that attenuates frequencies other than the frequency band for which the antenna array is designed. The filtered signal is channeled to signal probe  608 , which converts it to a corresponding electrical signal. The electrical signal is directed to circuit board  610 , which contains half of the circuitry shown in FIG.  2 . 
     The antenna elements used in the present invention may be characterized by their size in wavelengths at the frequency of interest, which is the frequency at which the antenna element is designed to transmit or receive. One typical antenna element configuration is termed a 1×1 antenna element or antenna element configuration. A 1×1 antenna element is approximately 2.1 wavelengths by 2.4 wavelengths in size. This asymmetric element provides substantially symmetric scan performance when a triangular grid is selected. This element provides a scan coverage of approximately ±8.7°×±8.7°. For a geostationary communications satellite, this scan supports global coverage. An example of an array module having 1×1 antenna elements is shown in FIG. 7 a . As shown, there are 64 1×1 antenna elements in this example. The 64 antenna elements are connected to 64 LNAs, arranged as eight amplifier/BFMM boards with eight LNAs per board. 
     An example of an array module having 2×1 antenna elements is shown in FIG. 7 b . A 2×1 antenna element is approximately 4.2 wavelengths by 2.4 wavelengths in size and provides a scan coverage of approximately±4°×±8.70°. This scan covers approximately half the viewable earth from geostationary orbit. As shown, there are 32 2×1 antenna elements in this example. The 32 antenna elements are connected to 32 LNAs, arranged as eight amplifier/BFMM boards with four LNAs per board. 
     An example of an array module having 1×2 antenna elements is shown in FIG. 7 c . A 1×2 antenna element is approximately 2.1 wavelengths by 4.8 wavelengths in size and provides a scan coverage of approximately±8.7°×±4°. As shown, there are 32 1×2 antenna elements in this example. The 32 antenna elements are connected to 32 LNAs, arranged as four amplifier/BFMM boards with eight LNAs per board. 
     An example of an array module having 1×4 antenna elements is shown in FIG. 7 d . A  1×4 antenna element is approximately 2.1 wavelengths by 9.6 wavelengths in size and provides a scan coverage of approximately±8.7°×±2°. As shown, there are 16 1×4 antenna elements in this example. The 16 antenna elements are connected to 16 LNAs, arranged as two amplifier/BFMM boards with eight LNAs per board. 
     An example of an array module having 4×1 antenna elements is shown in FIG. 7 e . A 4×1 antenna element is approximately 8.4 wavelengths by 2.4 wavelengths in size and provides a scan coverage of approximately±8.7°×±2°. As shown, there are 16 4×1 antenna elements in this example. The 16 antenna elements are connected to 16 LNAs, arranged as four amplifier/BFMM boards with four LNAs per board. 
     An example of an array module having 2×2antenna elements is shown in FIG. 7 f . A 2×2antenna element is approximately 4.2 wavelengths by 4.8 wavelengths in size and provides a scan coverage of approximately±4°×±4°. As shown, there are 16 2×2antenna elements in this example. The 16 antenna elements are connected to 16 LNAs, arranged as four amplifier/BFMM boards with four LNAs per board. 
     An example of an array module having 4×2 antenna elements is shown in FIG. 7 g . A 4×2 antenna element is approximately 8.4 wavelengths by 4.8 wavelengths in size and provides a scan coverage of approximately±2°×±4°. As shown, there are eight 4×2 antenna elements in this example. The eight antenna elements are connected to eight LNAs, arranged as two amplifier/BFMM boards with four LNAs per board. 
     An example of an array module having 2×4 antenna elements is shown in FIG. 7 h . A 2×4 antenna element is approximately 4.2 wavelengths by 9.6 wavelengths in size and provides a scan coverage of approximately±4°×±2°. As shown, there are eight 2×4 antenna elements in this example. The eight antenna elements are connected to eight LNAs, arranged as two amplifier/BFMM boards with four LNAs per board. 
     An example of an array module having 4×4 antenna elements is shown in FIG. 7 i . A 4×4 antenna element is approximately 8.4 wavelengths by 9.6 wavelengths in size and provides a scan coverage of approximately±2°×±2°. As shown, there are four 4×4 antenna elements in this example. The four antenna elements are connected to four LNAs, arranged as one amplifier/BFMM board with four LNAs per board. 
     A number of exemplary arrangements of array modules are summarized in table 800, shown in FIG.  8 . As shown, for each scan coverage requirement, there are two alternate embodiments available that can provide the same scan coverage. Within a particular scan coverage requirement, the embodiments differ in the beam quantity that they provide, and thus, differ in the quantities and locations of BFMMs that are used. Among scan coverage requirements, the embodiments differ in the type and quantity of antenna elements that are used and the quantities of amplifer/BFMM boards and beam combiners that are used. It will be seen that a very wide range of antenna capabilities can be provided using a relatively small range of standard parts. In this way, the design goal of providing scalability of coverage area and beam quantity with low development cost has been achieved. 
     There are several ways that particular antenna element configurations may be implemented. For example, a 2×2antenna element with a horn radiator may be implemented as a single horn of approximately 4.2 wavelengths by 4.8 wavelengths, or as four horns of approximately 2.1 wavelengths by 2.4 wavelengths. The choice of the particular implementation is an engineering decision, which may be made based on factors, such as size and weight of the antenna array, as well as cost. An example of a 2×2antenna element that is implemented as four horns of approximately 2.1 wavelengths by 2.4 wavelengths is shown in FIGS. 9 a-d.    
     FIG. 9 a  shows a front view of a 2×2antenna element implemented as a combination of four radiators. In particular, radiators  902 A,  902 B,  902 C, and  902 D are combined to form a single 2×2antenna element  904 . The direction of electrical field polarization in the radiators is shown by the arrows. A sectional view taken along plane “I” of FIG. 9 a  is shown in FIG. 9 b . As shown, each pair of radiators, such as radiator pair  902 C and  902 D, are coupled by waveguides  906  to a power divider  908 , which divides the signal power among the waveguides coupled to each radiator. A sectional view taken along plane “II” of FIGS. 9 a  and  9   b  is shown in FIG. 9 c . As shown, each radiator, such as radiators  902 B and  902 D, are coupled to a single waveguide, such as waveguide  906 . A sectional view taken along plane “III” of FIG. 9 a  is shown in FIG. 9 d . As shown, each waveguide that couples a radiator pair, such as waveguide  906 , is coupled by waveguides, such as waveguides  910  and  912 , to a power divider  914 , which divides the signal power among the waveguides. 
     An exemplary antenna element assembly  1000  is shown in FIG.  10 . Assembly  1000  includes an antenna element  1002 , waveguide portion  1004 , waveguide filter  1006 , and signal probe opening  1008 . In this example, antenna element  1002  is a slotted receiving antenna element that is made up of three subantenna elements  101 A,  1010 B, and  1010 C. Each sub-antenna element includes a plurality of receiving slots  1012 . Waveguide portion  1004  includes antenna element feed structure  1014 , which includes a plurality of antenna element feed slots  1016 . Signal probe opening  1008  provides the capability to insert a signal probe to convert the electromagnetic wave signals to electrical signals. 
     The exemplary antenna element assembly shown in FIG. 10 is designed to provide global coverage in geosynchronous orbit. Preferably the size is approximately 2.1 wavelengths by 2.4 wavelengths, at the design frequency. For example, antenna element assembly  1000  may be used at a design frequency of approximately 30 GHz, which results in antenna element  1002  having dimensions of approximately 0.83 inches by 0.94 inches. Even though this element contains 9 slots, it is functionally a 1×1 element, as described above regarding FIG. 7 a.    
     An exemplary antenna element assembly  1100  is shown in FIG.  11 . Assembly  1100  includes an antenna element  1102 , waveguide portion  1104 , waveguide filter  1106 , and signal probe opening  1108 . In this example, antenna element  1102  is a slotted receiving antenna element that is made up of six sub-antenna antenna elements  1110 A,  1110 B,  1110 C,  1110 D,  1110 E, and  1110 F. Each sub-antenna element includes a plurality of receiving slots  1112 . Waveguide portion  1104  includes antenna element feed structure  1114 , which includes a plurality of antenna element feed slots  1116 . Signal probe opening  1108  provides the capability to insert a signal probe to convert the electromagnetic wave signals to electrical signals. 
     The exemplary antenna element assembly shown in FIG. 11 is designed to provide coverage over a ±2°×±4° area (e.g., the continental United States (CONUS) from geosynchronous orbit). Even though this antenna has 72 slots, it is functionally a 4×2 element, as described above regarding FIG. 7 g . Preferably the size is approximately 4.2 wavelengths by 9.6 wavelengths, at the design frequency. For example, antenna element assembly  1100  may be used at a design frequency of approximately 30 GHz, which results in antenna element  1102  having dimensions of approximately 1.65 inches by 3.78 inches. This antenna element configuration provides horizontal polarization. If the complete antenna array is rotated through 90° the coverage area will be ±4° by ±2° (instead of ±2° by ±4°) and vertical polarization will be provided. 
     An exemplary antenna element assembly  1200  is shown in FIG.  12 . The antenna element assembly includes an antenna element  1202 , waveguide portion  1204 , waveguide filter  1206 , and signal probe opening  1208 . In this example, antenna element  1202  is a slotted receiving antenna element that is made up of  12  sub-antenna elements  1210 A- 1210 L. Each sub-antenna element includes a plurality of receiving slots  1212 . Waveguide portion  1204  includes antenna element feed structure  1214 , which includes a plurality of antenna element feed slots  1216 . Signal probe opening  1208  provides the capability to insert a signal probe to convert the electromagnetic wave signals to electrical signals. 
     The exemplary antenna element assembly shown in FIG. 12 is designed to provide coverage over a ±2°×±4° area (e.g., the continental United States (CONUS) from geosynchronous orbit). Preferably the size of each antenna element sub-assembly is approximately 4.2 wavelengths by 9.6 wavelengths, at the design frequency. For example, antenna element assembly  1200  may be used at a design frequency of approximately 30 GHz, which results in antenna element  1202  having dimensions of approximately 1.65 inches by 3.78 inches. This antenna element configuration provides vertical polarization. If the complete antenna array is rotated through 90° the coverage area will be ±4°×±2° (instead of ±2°×±4°) and horizontal polarization will be provided. 
     As can be seen from FIG. 1, the present invention includes a number of similar elements, which are similarly connected. An important aspect of the present invention is the repetitive and modular packaging and connection of these similar elements. A modular building block, according to the present invention, as well as constituent portions of the building block, are shown in FIGS. 13-20. A partially built-out circuit board assembly  1300 A, which is included in the present invention, is shown in FIG.  13 . Circuit board assembly  1300 A includes circuit board  1302 A, mounting plate  1304 , and a plurality of waveguide assemblies  1306 A- 1306 D. Circuit board assembly  1302 A contains substantially all of the circuitry shown in FIG. 2, which illustrates an amplifier/BFMM board. Circuit board  1302 A includes connectors  1308 A and  1308 B, which provide electrical power and radio frequency (RF)/control signal connection of circuit board  1302 A with the remainder of the antenna system. 
     Mounting plate  1304  is attached to circuit board  1302 A and provides a means of mounting waveguide assemblies, such as assemblies  1306 A- 1306 D, to circuit board  1302 A. Mounting plate  1304  includes a plurality of waveguide mounting positions, such as waveguide mounting position  1310 , for mounting waveguide assemblies. In FIG. 13, four waveguide assemblies are shown, but mounting plate  1304  is shown as having eight waveguide mounting positions. A key feature of the present invention is the capability to populate all, or only a portion, of the available mounting positions. Each waveguide mounting position  1310  includes a waveguide channel  1312  (also shown in FIG. 6 as item  612 ) and a plurality of mounting holes  1314 . Waveguide channel  1312  provides a continuation of the waveguide cavity for the attached waveguide, so as to transmit the radio frequency signal to the signal probe. Mounting holes  1314  allow mounting of the waveguide assemblies to mounting plate  1304 . 
     Each waveguide assembly, such as waveguide assembly  1306 A, includes a first mounting bracket  1316 , a second mounting bracket  1318 , a waveguide portion  1320  (also shown on FIG. 6 as item  604 ), and a waveguide filter  1322  (also shown in FIG. 6 as item  606 ). The first mounting bracket  1316  provides the capability to mount the waveguide assembly on mounting bracket  1304 . The second mounting bracket  1318 , which is located at the other end of waveguide assembly  1306 A from the first mounting bracket  1316 , provides the capability to mount an antenna element to waveguide assembly  1306 A. Waveguide portion  1320  is provided to allow the antenna element to be placed in the desired physical location relative to circuit board  1302 A. Typically, waveguide portion  1320  includes one or more bends or jogs, which provide the proper positioning of the antenna element. Waveguide filter  1322  provides bandpass filtering to attenuate spurious and other unwanted signals that are not in the frequency band being used for communications. 
     The circuit board assembly shown in FIG. 13, along with additional installed components, is shown in FIG.  14 . In FIG. 14, all eight mounting positions are shown as being populated with waveguide assemblies  1306 A- 1306 H. In addition, antenna elements  1402 A- 1402 D (also. shown in FIG. 6 as  602 ) are shown mounted on waveguide assemblies  1306 A- 1306 H. Mounting bracket  1404  is attached between the antenna elements and the waveguide assemblies to structurally couple to each other the ends of the waveguide assemblies to which the antenna elements are attached. Mounting bracket  1404  provides structural rigidity to the waveguide assemblies. The antenna elements shown in FIG. 14, such as antenna element  1402 A, are horn antennas. Horn antenna elements are shown as an example only, the present invention contemplates other antenna element structures, such as slotted antenna elements. 
     Two circuit board assemblies, each similar to the circuit board assembly shown in FIG. 14, are shown in FIG.  15 . In FIG. 15, two circuit board assemblies  1300 A and  1300 B are shown positioned next to each other. Circuit board assembly  1300 A is shown fully built out and assembled. Circuit board assembly is shown with all waveguide mounting positions occupied by antenna element assemblies  1402 A- 1402 H. As described, each antenna element assembly incorporates a waveguide assembly, which typically includes one or more bends or jogs to provide the proper positioning of the antenna element. In one embodiment, waveguide assemblies attached to adjacent circuit board assemblies have bends or jogs that are opposite to each other, which allows placement of the antenna elements on a triangular grid. For example, as shown in FIG. 14, antenna element assemblies  1402 A- 1402 H, which are attached to circuit board assembly  1300 A, include bends or jogs to the left, while waveguide assemblies  1306 A  1306 H, which are attached to adjacent circuit board assembly  1300 B, include bends or jogs to the right. Thus, antenna elements that are attached to adjacent circuit board assemblies may be placed on a triangular grid. The placement of antenna elements on a triangular grid may be seen more clearly by reference, for example, to FIG.  15 . The waveguide mounting positions  1310  (FIG. 13) may be arranged on a square grid to ease manufacturing and assembly. 
     The circuit board assemblies shown in FIG. 15 are also shown in FIG.  16 . In FIG. 16, mounting bracket  1604  is shown attached to mounting plate  1602 . Mounting bracket  1604  provides structural rigidity to the antenna element assemblies. 
     An antenna array module  1700  is shown in FIG.  17 . In FIG. 17, module  1700  is shown partially built-out with four fully populated circuit board assemblies  1300 A,  1300 B,  1300 C, and  1300 D. Module brackets  1702 ,  1704  and  1706  have been attached to the circuit board assemblies to provide additional structural integrity to module  1700 . 
     Antenna array module  1700 , shown in FIG. 17, is also shown in FIG.  18 . In FIG. 18, module  1700  is shown with eight fully populated circuit board assemblies  1300 A,  1300 B,  1300 C,  1300 D,  1300 E,  1300 F,  1300 G, and  1300 H. 
     A rear view of antenna array module  1700 , shown in FIG. 18, is shown in FIG.  19 . In FIG. 19, module  1700  includes backplane assembly  1902 A, which is connected to connectors on each circuit board in module  1700 . For example, connector  1904  of circuit board  1906  is connected to backplane assembly  1902 A. Typically, backplane assembly  1902 A includes a plurality of backplane circuit boards, such as backplane circuit board  1908 . Backplane assembly  1902 A would contain, for example, for the configuration shown in FIG. 3, power combiners  306 A-A to  306 A-M. Backplane circuit board  1908  may contain, for example, two such power combiners. 
     A rear view of antenna array module  1700 , shown in FIG. 19, is also shown in FIG.  20 . In FIG. 20, module  1700  includes two backplane assemblies  1902 A and  1902 B, which are connected to connectors on each circuit board in module  1700 . In addition, module  1700  is shown including backplane bracket  2002 , which fastens backplane assemblies  1902 A and  1902 B to the circuit boards in module  1700 . Backplane bracket  2002  provides additional structural integrity for module  1700 . For simplicity, the beam connectors, the antenna array module DC/DC converter and control interface assemblies are not shown. 
     An example of a complete antenna array  2100 , which includes sixteen antenna array modules  2100 A- 2100 P, is shown in FIG.  21 . The sensitivity of the receive array to collect incoming signals is proportional to the number of array modules used. The array modules have been designed so that any number of them may be combined. In this way, the design goal of modularity with respect to receive sensitivity has be achieved. Antenna array modules  2100 A-P interlock, to form a contiguous antenna array structure. The modules used have overlapping of antenna elements and circuit board assemblies within each module, but also between two modules. Thus, adjacent modules overlap. For example, module  2100 B overlaps module  2100 A. In particular, antenna element  2102  overlaps a circuit board included in module  2100 B. Although this overlapping does present manufacturing and assembly challenges, it is required to achieve good antenna performance and provides good packing density of antenna elements and modules. Conventional radio frequency (RF), control, and DC power harnesses are used to electrically connect the antenna array modules to form the complete antenna array. 
     Preferably, for a given embodiment, all circuit boards are of similar design. For example, all circuit boards may be designed to accommodate the circuitry (LNAs and beamformers) needed to handle eight antenna elements and 32 beams. A feature of the present invention is that these similar circuit boards may be fully populated or partially populated. In this example, a fully populated circuit board would have mounted on it the circuitry needed to handle eight antenna elements and 32 beams. A partially populated circuit board would have mounted on it the circuitry needed to handle only four or two antenna elements, with 16 or 32 beams, or eight antenna element with 16 beams. The board itself includes the interconnections needed to accommodate eight antenna elements and 32 beams. Thus, the present invention can accommodate antenna arrays having varying numbers of antenna elements and beams without requiring redesign of the circuit boards, or the modules mounted to the board, for each embodiment. This means that the present invention can support applications with very different coverage/scan and beam quantity requirements by using standard building blocks. This reduces the cost/risk and time required to fabricate an antenna array for an application with a different coverage/scan and beam quantity requirement. 
     FIG. 22 shows the electrical connections between the antenna array modules  2100 A-P that are contained within the complete antenna array  2100 . As shown in FIG. 5, each antenna array module has M (where M is 32 in a preferred embodiment) beam outputs. These beam outputs are connected with M RF harnesses  2206 A-M. Each RF harness contains a P:1 way power combiner  2208 A-M to combine the signals from the array modules. Each power combiner is connected to one of the array beam ports. Control signals are distributed to/from the antenna array modules using control harness  2204 . DC power is distributed to the antenna array modules using DC power harness  2202 . 
     FIG. 23 shows a transmit embodiment of the present invention. It can be seen that FIG. 23 is very similar to FIG.  1 . However the low noise amplifiers  104 A- 104 N in FIG. 1 are replaced by power amplifiers  2304 A- 2304 N in FIG.  23 . Each output of a beamformer  2306 A- 2306 N is connected to the input to a power amplifier. Each output of a power amplifier is connected to the input to a radiating element assembly  2302 A- 2302 N. 
     FIG. 24 shows a transmit/receive embodiment of the present invention. This implementation is of interest for radar and half duplex communications applications. It can be seen that FIG. 24 is very similar to FIG.  1 . However the Low Noise Amplifiers (LNAs)  104 A- 104 N in FIG. 1 are replaced by duplexed amplifier pairs  2404 A- 2404 N in FIG.  24 . Each duplexed amplifier pair consists of a power amplifier  2416 N and an LNA  2418 N connected between a pair of duplexers  2420 N and  2422 N. In transmit operation the signal emanating from a beamformer  2406 N is connected by duplexer  2422 N to the input of the power amplifier  2416 N. The output of this power amplifier is connected by duplexer  2420 N to the input of radiating element assembly  2402 N. In receive operation the signal emanating from radiating element assembly  2402 N is connected by duplexer  2420 N to the input of LNA  2418 N. The output of this LNA is connected by duplexer  2422 N to the input of beamformer  2406 N. The duplexers may be implemented as switches or circulators. 
     Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that the present invention contemplates other embodiments as well. For example, in some applications it may be desired to provide an amplitude taper across the antenna aperture to reduce sidelobe levels (as is well understood by those of.skill in the art). In this case, a phase shifter/attenuator may be used-instead of a phase shifter ( 114 A,  114 M in FIG.  1 ). Also in some applications it may be desired to implement the phased array antenna using intermediate frequency (IF) beamforming. In this case up/down converter circuits and local oscillator distribution circuits must be added. The architecture used to interconnect these additional components is well known to those of skill in the art. Circular polarization may also be achieved by adding an external polarizer or by using circularly polarized antenna elements. 
     In addition, one of skill in the art would recognize that there are other embodiments that are equivalent to the described embodiments. For example, different quantities of components and/or elements could be used in any subassembly, or different radiating elements and/or filter types could be used. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.