Abstract:
A space-fed conformal array for a high altitude airship includes a primary array lens assembly adapted for conformal mounting to a non-planar airship surface. The lens assembly includes a first set of radiator elements and a second set of radiator elements, the first set and the second set spaced apart by a spacing distance. The first set of radiators faces outwardly from the airship surface to provide a radiating aperture. The second set of radiators faces inwardly toward an inner space of the airship, for illumination by a feed array spaced from the second set of radiators.

Description:
This invention was made with Government support under Contract No. HR0011-04-C-0096 awarded by the Defense Advanced Research Projects Agency. The Government has certain rights in this invention. 

   BACKGROUND 
   Airborne sensor arrays provide challenges in terms of weight and power limitations. Reducing weight and power requirements is a typical objective for airborne and space sensor arrays. 
   SUMMARY OF THE DISCLOSURE 
   A space-fed conformal array for a high altitude airship includes a primary array lens assembly adapted for conformal mounting to a non-planar airship surface. The lens assembly includes a first set of radiator elements and a second set of radiator elements, the first set and the second set spaced apart by a spacing distance. The first set of radiators faces outwardly from the airship surface to provide a radiating aperture. The second set of radiators faces inwardly toward an inner space of the airship, for illumination by a feed array spaced from the second set of radiators. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an exemplary airship in simplified isometric view. 
       FIG. 2  is a simplified schematic block diagram illustrating a dual band electronically steerable array (ESA) system suitable for use on the airship of  FIG. 1 .  FIG. 2A  illustrates an exemplary feed array for dual band operation.  FIG. 2B  illustrates a fragment of an X-band feed array portion of the dual band feed array. 
       FIG. 3A  diagrammatically illustrates two exemplary feed locations for an exemplary nose cone planar array. 
       FIG. 3B  diagrammatically illustrates several exemplary locations for a feed array for an exemplary conformal side array. 
       FIG. 4A  is an isometric view of an airship with a conformal side array positioned on one flank.  FIG. 4B  is an enlarged view of a portion of the airship and array within circle  5 B depicted in  FIG. 4A , depicting some of the tile panels.  FIG. 4C  is an isometric view of one tile panel, depicting its front face.  FIG. 4D  is an isometric view similar to  FIG. 4C , but depicting the back face of the tile panel. 
       FIG. 5  is an isometric view of a tile panel, illustrating structural stand offs and twin lead feed lines connecting to vertical bow-tie UHF dipole elements. 
       FIG. 6  is a close-up isometric view of a portion of the tile panel of  FIG. 5 .  FIG. 6A  depicts a fragment of an exemplary embodiment of an X-band lens array formed on a board assembly. 
       FIG. 7  is an isometric view of a tile panel, diagrammatically illustrating long slot radiators, feed probes and phase shifter electronics. 
       FIG. 8  is a schematic diagram of a space-fed array operable either as a feed through lens array or a reflective array.  FIG. 8A  illustrates one set of 180 degree phase shifters of the array of  FIG. 8 , connected through a switch.  FIGS. 8B-8C  are exemplary schematic diagrams of alternate embodiments of a phase shifter/switch set. 
       FIG. 9  is a schematic diagram of an exemplary embodiment of RF circuitry between a twin wire transmission line feed and a UHF long slot element. 
       FIG. 10  diagrammatically depicts an exemplary embodiment of placement of phase shifter and balun circuitries across a portion of a UHF long slot radiator. 
       FIG. 11  is a schematic diagram of an exemplary embodiment of X-band lens array circuitry. 
     FIGS.  12  and  12 A- 12 C are schematic diagrams illustrating an exemplary embodiment of an RF connection in the form of a caged coaxial interconnect line between respective phase shifter circuit halves. 
     FIGS.  13  and  13 A- 13 D are schematic diagrams illustrating an exemplary embodiment of a coupled microstrip transition to orthogonally mounted coplanar strip (CPS) transmission line. 
   

   DETAILED DESCRIPTION 
   In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals. The figures are not to scale, and relative feature sizes may be exaggerated for illustrative purposes. 
   An exemplary vehicle on which a sensor or antenna array may be installed is an airship, i.e. a lighter-than-air craft. Antenna arrays and components described below are not limited to this application, however. For the sake of this example, the airship may be a stratospheric craft on the order of 300 meters in length. The airship may be preferably semi-rigid or non-rigid in construction. The airship may include an outer balloon structure or skin which may be inflated, with internal ballonets filled with air to displace helium in the airship for airlift control. 
     FIG. 1  shows an exemplary airship in simplified isometric view. The airship  10  includes an outer skin surface  12 , a nosecone region  20 , a stern region  30 , horizontal fins  32  and a vertical tail fin  34 . Propulsion pods  36  are provided and may include propellers and drive units. An avionics and systems bay  40  is provided on the underbelly of the airship. The interior of the airship may include a helium bay portion  22  separated from the remainder of the interior by a bulkhead  24 . 
   In an exemplary embodiment, the airship  10  carries a space-fed dual band antenna, comprising a plurality of arrays. In an exemplary configuration, the space-fed dual band antenna arrays may each operate as a feed-through lens or reflective array. In this exemplary embodiment, one conformal array  50  is installed with a primary array  52  on a flank of the airship to provide antenna coverage of the left and right side relative to the airship, and one planar array  70  with a primary array  72  ( FIG. 3A ) on the bulkhead  24  in a nose region to cover the front and back regions relative to the airship. In an exemplary embodiment, the primary array of the side array  50  may measure on the order of 25 m×40 m, while the primary array  72  ( FIG. 4A ) of the planar array  70  in the nosecone region may be about 30 m×30 m in size. 
   In an exemplary embodiment, each of the space-fed arrays employs a dual-band shared aperture design. An exemplary embodiment of a lens array includes two facets, a pick-up side with the elements facing the feed (power source) and the radiating aperture. A space-fed design may simplify the feed network and reduce the RF insertion and fan-out loss by distributing the RF power through the free space to a large number of radiating elements (4 million for X-band, and about 6000 for a UHF band in one exemplary embodiment). DC and low power beam scan digital command circuitry may be sandwiched inside the lens array in an exemplary embodiment. The RF circuit portion may be separated from the DC and digital electronics circuit portion. 
     FIG. 2  is a simplified schematic block diagram illustrating a dual band electronically steerable array (ESA) system suitable for use on the airship  10 . The avionics bay  40  has mounted therein a set of power supplies  40 - 1 , high band (X-band) receivers  40 - 2 , low band (UHF) receivers  40 - 3  and  40 - 5 , a low band exciter  40 - 4 , an X-band exciter  40 - 6 , and a controller  40 - 7  including a master beam steering controller (BSC)  40 - 8 . The receivers and exciters are connected to the feed array  100 . In this exemplary embodiment, the X-band feed array  100 B is divided into a receive channel including a set  100 B- 1  of radiator elements, and a transmit channel including a set  100 B- 2  of radiator elements. 
   In an exemplary embodiment, the receive channel includes, for each radiator element  100 B- 1 , a low noise amplifier, e.g.  100 B- 1 A, whose input may be switched to ground during transmit operation, an azimuth RE feed network, e.g. network  100 B- 1 B, a mixer, e.g.  100 B- 1 C, for mixing with an IF carrier for down converting received signals to baseband, a bandpass filter, e.g.  100 B- 1 D, and an analog-to-digital converter (ADC), e.g.  100 B- 1 E, for converting the received signals to digital form. The digitized signals from the respective receive antenna elements  100 B- 1  are multiplexed through multiplexers, e.g. multiplexer  100 B- 1 F and transmitted to the X-band receivers  40 - 2 , e.g., through an optical data link including fiber  100 B- 1 G. 
   In an exemplary embodiment, the transmit X-band channel includes an optical fiber link, e.g. fiber  100 B- 3 , connecting the X-band exciter  40 - 6  to an optical waveform control bus, e.g.  100 B- 4 , having outputs for each set of radiating elements  100 B- 2  to respective waveform memories, e.g.  100 B- 5 , a digital-to-analog converter, e.g.  100 B- 6 , a lowpass filter, e.g.  100 B- 7 , an upcoverting mixer  100 B- 8 , an azimuth feed network  100 B- 10 , coupled through a high power amplifier, e.g.  100 B- 11  to a respective radiating element. The control bus may provide waveform data to the waveform memory to select data defining a waveform. 
   In an exemplary embodiment, the low-band feed array includes a transmit/receive (T/R) module, e.g.  100 A- 1 A, for each low-band radiator element, coupled to the respect receive and transmit low-band channels. The T/R modules each include a low noise amplifier (LNA) for receive operation and a high power amplifier for transmit operation. The input to the low noise amplifiers may be switched to ground during transmit operation. In an exemplary embodiment, the outputs from adjacent LNAs may be combined before downconversion by mixing with an IF carrier signal, e.g. by mixer  100 A- 1 B. The downconverted signal may then be passed through a bandpass filter, e.g.  100 A- 1 C, and converted to digital form by an ADC, e.g.  100 A- 1 D. The digitized received signal may then be passed to the low band receivers, e.g.  40 - 3 , for example by an optical data link including an optical fiber  100 A- 1 E. 
   In an exemplary embodiment, the transmit low-band channel includes the low band exciter  40 - 4 , a waveform memory  100 A- 1 G, providing digital waveform signals to a DAC, e.g.  100 A- 1 H, a low pass filter, e.g.  100 A- 1 I, and an upconverting mixer, e.g.  100 A- 1 J, providing a transmit signal to the T/R module for high power amplification and transmission by the low band radiating elements of the array  100 A. 
     FIG. 2  also schematically depicts an exemplary lens array, in this case array  50 , which is fed by the feed array  100 . The array  50  includes the pick up array elements on the side facing the feed array, and the radiating aperture elements facing away from the feed array. Exemplary embodiments of feed arrays will be described in further detail below. 
     FIG. 2A  illustrates a fragment of an exemplary feed array  100  for dual band operation, showing exemplary low band radiating elements and high band radiating elements. This example includes 4-8 rows of radiating elements spaced and weighted to produce a proper feed pattern in the elevation (EL) plane with minimum spillover and taper loss. This is a practice known to a skilled designer and is similar to a situation encountered in a reflector antenna design. For example, the array  100  includes a UHF feed array  100 A, comprising 4 rows of radiating elements  100 A- 1 . An exemplary suitable radiating element is a flared notch dipole radiating element described, for example, in U.S. Pat. No. 5,428,364. The rows of radiating elements have a longitudinal extent along the airship axis. The array  100  further includes an X-band feed array  100 B, arranged along a top edge of the UHF feed array  100 A. The X-band feed array may, in an exemplary embodiment, be a scaled version of the UHF feed array  100 A, and similar radiating elements may be employed in the X-band feed array  100 B as for the UHF array. Other radiating elements may alternatively be employed, e.g. radiating patches or slots. In an exemplary embodiment, the X-band array  100 B has a longitudinal extent which may the same length as the UHF array, but its height is much smaller, since the size of the radiating elements are scaled down to the wavelength of a frequency in the X-band. 
     FIG. 2B  shows a fragmentary, broken-away portion of the X-band array  100 B, with an array of radiating elements  100 B- 1 . The top layer  100 B- 2  may be a protective dielectric layer or cover. 
   The feed array  100  is oversized in length along the airship axis, about 48 m in this embodiment; so that signals returned from a wide region in the azimuth (horizontal) direction may be focused in the feed region with minimal spillover. In an exemplary embodiment, the signals include multiple beams synthesized by a digital beam former, e.g. beamformer  40 - 8  ( FIG. 2 ). 
   Feed location and the structural support for the placement of the feed array may be traded off, based on the consideration of factors such as instantaneous bandwidth, construction issues of the airship and weight distribution. 
     FIG. 3A  diagrammatically illustrates two exemplary feed locations for the nose cone planar array  70 . For this array, the primary lens array  72  is mounted on the bulkhead  24 , which is generally orthogonal to the longitudinal axis of the airship. One exemplary location for the feed array  80  for this array is at the top of the outer surface of the airship skin, and is denoted by reference  80 - 1 . A second exemplary location for the feed array for planar array  70  is at the bottom of the airship, denoted by reference  80 - 2 . In an exemplary embodiment, the feed array is oversized in length with respect to the primary array, e.g. 20% longer than a 30 m length of the primary array. In an exemplary embodiment, the feed array may be mounted on the outside of the airship. The feed array may be curved to conform to the outer surface of the airship, and phase corrections may be applied to the feed array to compensate for the curvature. 
     FIG. 3B  diagrammatically illustrates several exemplary locations for the feed array  54  for the conformal side array  50 . For this array, the primary lens array  52  is mounted on a flank of the skin surface of the airship. The feed array  60  may be mounted at one of many locations, to produce a feed-through beam  56 A and a reflected beam  54 B. For example, one exemplary feed array  60 - 1  is located within the interior space of the airship. The feed array  60 - 1  may be implemented with a relatively small feed array, less than one meter in height in one exemplary embodiment, which may be relatively light and with a wide bandwidth, and provides a relatively small blockage profile for energy reflected by the primary array  52 . Feed array  60 - 2  is mounted on the skin surface of the airship, at a location close to the top of airship. Feed array  60 - 3  is mounted within the interior space of the airship, at approximately a center of the interior space facing the primary feed array. The location of  60 - 3  may be undesirable for ballonet airship construction. Another location is that of feed array  60 - 4 , on a lower quadrant of the skin surface on a side of the airship opposite that of the primary feed array. This location may provide good weight management, but may be undesirable in terms of bandwidth. A fifth location is that of feed array  60 - 5 , which is located on the same side of the airship as feed array  60 - 4  but in the upper quadrant. 
   For some applications, the location of feed array  60 - 5  may provide better performance relative to the locations of feed arrays  60 - 1  to  60 - 4 . Depending on the location of the feed array, different electrical lengths to the respective top and bottom edges of the primary array from the feed array may create different time delays, making it more difficult to use phase shifters to correct for the different path lengths. Location  60 - 5  results in fairly closely equal path lengths (from feed array to top of primary array and to bottom of feed array. 
   In an exemplary embodiment, the flank-mounted dual-band aperture  50  includes a primary array  52  formed by many one-square-meter tile panels  54 , as shown in  FIG. 5 , e.g. one thousand of the tile panels for a one thousand square meter aperture size. In this example, the array  52  is 25 m by 40 m, although this particular size and proportion is exemplary; other primary arrays could have tiles which are larger or smaller, and be composed of fewer or larger numbers of tiles. The tiles may be attached to the outer skin of the airship, e.g., using glue, tie-downs, rivets, snap devices or hook and loop attachments. One exemplary material suitable for use as the skin is a 10 mil thick fluoropolymer layer with internal Vectran™ fibers. Another exemplary skin material is polyurethane with Vectran™ fibers. 
     FIG. 4A  is an isometric view of the airship  10  with the conformal side array  52  positioned on one flank.  FIG. 4B  is an enlarged view of a portion of the airship and array within circle  4 B depicted in  FIG. 4A , depicting some of the tile panels  54 . 
     FIG. 4C  is an isometric view of one tile panel  54 , depicting the front face of the tile panel.  FIG. 4D  is an isometric view similar to  FIG. 4C , but depicting the back face of the tile panel  54 . 
     FIG. 4C  illustrates features of an exemplary UHF band lens assembly, comprising spaced dielectric substrates  54 - 1  and  54 - 2 . In an exemplary embodiment, the substrates  54 - 1  and  54 - 2  may be fabricated on flexible circuit boards. In an exemplary embodiment for a UHF band, the substrates are spaced apart a spacing distance of 15 cm. Fabricated on the front face  54 - 2 A of substrate  54 - 2  are a plurality of spaced long slot radiators  54 - 3 . The radiators are elongated slots or gaps in a conductive layer pattern. The slots  54 - 3  may be formed in the conductive layer on the front surface by photolithographic techniques. In an exemplary UHF embodiment, the slots have a relatively large width, e.g. 4 cm, which allows room to place UHF circuit devices, e.g phase shifter and switch structures, in the slot opening. In one exemplary embodiment, the radiator slots are fed by probes, e.g. probes  54 - 7  ( FIG. 7 ) coupled to dipole pick up elements  54 - 6  ( FIG. 6 ). In an exemplary embodiment, the long slot radiators are disposed at an orthogonal polarization relative to the dipole pick up elements. Long slot radiators as described in US 2005/0156802 may be employed in an alternate embodiment. 
     FIG. 4D  illustrates the back face of the tile  54 , and features of an X-band lens assembly. In an exemplary embodiment, the X-band lens array is fabricated on board assembly  54 - 2 , and may be constructed by standard procedures using multi-layer circuit board technology (RF-on-flexible circuit board layers) to package the DC and digital beam control electronics. The total thickness of the X-band lens array assembly is about 2 cm back to back in an exemplary embodiment, for one wavelength at an X-band operating frequency, while the low band aperture is about 17 cm thick, with 15 cm quarter-wave spacing for a wire mesh or grid  54 - 1 B ( FIG. 4D ) from the long slot radiators. 
   Still referring to  FIG. 4D , the back face  54 - 1 A of substrate  54 - 1  has formed thereon a wire grid  54 - 1 B. In an exemplary embodiment, the wire grid may be fabricated using photolithographic techniques to remove portions of a conductive layer, e.g., a copper layer, formed on the surface to define separated conductive wires on the dielectric substrate surface. The conductive wires of the grid are disposed in an orthogonal sense relative to the long slot radiators  54 - 3 . The wire grid or thin-wire mesh  54 - 1 B serves as a reflecting ground plane for the long slot radiator elements  54 - 3 . In an exemplary UHF embodiment, the spacing of the thin wires may be about 6 cm, or one tenth of a wavelength at UHF band. The long slots radiate a field horizontally polarized, chosen for the low band applications including foliage penetration. In an exemplary embodiment, the wire grid may have virtually no effect on X-band operation, due to the wide spacing at X-band wavelengths. 
     FIGS. 5-7  illustrate an exemplary dual-band aperture design for the primary array  52  in further detail.  FIG. 5  is an isometric view of a tile panel  54 , illustrating the separation between the substrates  54 - 1  and  54 - 2 . and depicting structural stand offs  54 - 4  between the substrates.  FIG. 6  is an inverted close-up isometric view of a portion of the tile panel of  FIG. 5 , showing a bow-tie dipole element  54 - 6 , a corresponding twin-wire feed line  54 - 5  and a long slot radiator  54 - 3 . The standoffs are positioned outside the skin of the airship, in an exemplary embodiment. The twin lead feed lines  54 - 5  connect to respective vertical bow-tie UHF dipole elements  54 - 6 . 
   Each bow-tie dipole element  54 - 6  picks up power from the feed array  60 , and transfers the power to a long slot element on the front face through a pair of twin-wire feed lines  54 - 5  with a polarization 90 degree twist. The signal goes through a phase shifter and excites the long slot through a feed probe  54 - 7 . The phase shifter and a lumped element transformer matching the impedance of the radiator at each end are sandwiched in a multi-layer circuit board shared inside the X-band array. 
   The X-band elements are vertically polarized, and positioned on both the pick-up side and the radiating side of the aperture, as illustrated in  FIGS. 6 ,  6 A and  7 . Rows of X-band elements  54 - 8  are fabricated on dielectric substrate strips  54 - 9  which are supported in parallel, spaced relation on both sides of the substrate  54 - 1  in an exemplary embodiment. The dielectric substrates  54 - 9  are attached orthogonally to the substrate  54 - 1 , and extend parallel to the long slot radiators  54 - 3 . The X-band elements  54 - 8  in an exemplary embodiment may be radiating elements described, for example, in U.S. Pat. No. 5,428,364. An exemplary spacing between the X-band radiator strips  54 - 9  is one-half wavelength at X-band, about 0.6 inch (1.5 cm).] 
     FIG. 6A  depicts a fragment of an exemplary embodiment of the X-band lens array formed on board assembly  54 - 1 . The X-band radiator strips  54 - 9  in an exemplary embodiment are each on the order on one cm in height, with a spacing of one half wavelength. The substrate assembly  54 - 1  may include a multilayer printed circuit board, in which the conductive layer defining the UHF long slot radiators is buried. X-band phase shifter circuits and control layers, generally depicted as  54 - 10  may also be embedded within the multilayer circuit board assembly. Low band electronics may also be embedded within the multilayer printed circuit board assembly. A ground plane and cover layer  54 - 11  is disposed between the strips. 
   In an exemplary embodiment, a polarization twist isolates high band and low band signals, and also between the pick-up side and the radiating side of the lens array. On transmit, both the low band (UHF) and high band (X-band) sources transmit vertically (V) polarized signals to the lens array. The H-polarized mesh ground plane  54 - 1 B is transparent to these transmitted signals. The UHF pick-up elements or dipoles  54 - 6  pick up the vertically polarized signal, transfers the power through the twin-wire feed  54 - 5  to excite the long slot  54 - 3 , which radiates an H-polarized wave into space. An H-polarized wave radiates backward, but will be reflected by the orthogonal H-polarized mesh  54 - 1 B. 
   A polarization twist isolates the pickup side and the radiating side of the UHF lens array, i.e the twist between the dipole pickup elements  54 - 6  and the long slots  54 - 3 . For X band, there is a ground plane (see  FIG. 6A ), which isolates the pickup elements on the bottom and the radiating elements on the top. The radiating elements are spaced one quarter wavelength from the groundplane, and the pickup elements are also spaced one quarter wavelength from the ground plane. The grid  54 - 1 B provides a groundplane for the UHF long slot radiators only; the ground plane for the X-band lens also serves as the ground plane for the UHF dipoles. Thus, for the UHF array, the pickup and the radiating elements do not share a common ground plane. Since the dipoles  54 - 6  are at cross-polarization to the wire grid  54 - 1 B, the dipoles can be located close to the wire grid without impacting performance. Effectively the distance between the pickup elements and the radiating elements may be one-quarter wavelength instead of one-half wavelength, a reduction is size which may be important at UHF frequencies. 
     FIG. 7  is an isometric view of a tile panel  54 , diagrammatically illustrating long slot radiators  54 - 3 , feed probes  54 - 7  and phase shifter electronics. 
   In an exemplary embodiment, a space-fed array can be operated as a feed-through lens or as a reflective array, depending on which side of the airship is to be covered. This may be accomplished in an exemplary embodiment by separating the phase shifter circuitry between the pick up and radiating aperture elements into two halves, each providing a variable phase shift between 0 and 180 degrees, and inserting a switch at the mid-point to allow the signal to pass through or be reflected. An exemplary embodiment is depicted in  FIG. 8 , a schematic diagram of a space-fed array. 
     FIG. 8  illustrates space-fed array  50 , comprising a primary array  52  and a feed array  60 . The feed array  60  includes a plurality of feed radiating elements  68 A, a plurality of T/R (transmit/receive) modules  68 B and a feed network  68 C. RF energy is applied at I/O port  68 D, and is distributed through the feed network and the T/R modules to the respective feed elements, to form a beam  66  which illuminates the primary array  52 . The primary array  52  includes a first side set of radiating elements  58 A, a first set of 180 degree phase shifters  58 B, a set of switches  58 C, a second set of 180 degree phase shifters  58 D and a second set of radiating elements  58 E. 
     FIG. 8A  illustrates an exemplary embodiment of one set of 0 to 180 degree analog phase shifters  58 B,  58 D of the array of  FIG. 8 , connected through a switch  58 C. The switch  58 C selectively connects the midpoint node  58 F between the phase shifters to ground. When in the open position, energy from one set of phase shifter/radiating element passes through the node to the opposite phase shifter/radiating element. This is the feed through mode position. When the switch is closed, creating a short to ground, energy arriving at the midpoint node is reflected by the short circuit, providing a reflection mode. 
     FIG. 8B  is a simplified schematic diagram of an exemplary embodiment of a switch and phase shifter circuit suitable for implementing the circuit elements of  FIG. 8A  for the low band (UHF). In this exemplary embodiment, the filters  58 B- 1  and  58 D- 1  are implemented as tunable lumped element filter phase shifters, with the tunable elements provided by varactor diodes biased to provide variable capacitance. The switch  58 C- 1  may be implemented by a shunt diode or MEMS switch. The switches and tunable elements may be controlled by the beam steering controller  50 - 1  ( FIG. 2 ). 
     FIG. 8C  is a simplified schematic diagram of an exemplary embodiment of a switch and phase circuit suitable for implementing the circuit elements of  FIG. 8A  for the high band (X-band). In this exemplary embodiment, the filters  58 B- 2  and  58 D- 2  are implemented as reflection phase shifters each comprising a 3 dB hybrid coupler and varactor diodes to provide variable capacitance. Reflection phase shifters are described, for example, in U.S. Pat. No. 6,741,207. The switch  58 C- 2  may be implemented by a shunt diode or MEMS switch. 
   In an exemplary embodiment of a UHF lens array, each UHF bow-tie dipole element  54 - 6  picks up power from the UHF feed array and transfers the power to a UHF long slot element  54 - 3  on the front face of substrate  54 - 2  via a twin wire transmission line feed  54 - 4 .  FIG. 9  is a schematic diagram of an exemplary embodiment of RF circuitry between a twin wire transmission line feed  54 - 4  and a long slot element  54 - 3 . A lumped element balun  54 - 10 , varactor diodes  54 - 12 , a PIN diode  54 - 13 , DC blocking capacitors  54 - 14  and inductors  54 - 11  are packaged as surface mounted devices (SMD) and are mounted on top of a multilayer RF flexible circuit board comprising substrate  54 - 2 . A microstrip line may used to connect the SMD s together to form a switched varactor lumped element filter phase shifter circuit. A shift in transmission phase through the lumped element filter is the result of changing the capacitance of the varactor as the bias voltage is varied across the varactor devices. The PIN diode  54 - 13  serves a shunt switch in the center of the phase shifter circuit. Each end of the phase shifter circuit is connected to the single ended ports of the baluns  54 - 10  and  54 - 15  which essentially are lumped element transformers that provides impedance matching and transmission line mode conversion to both the orthogonally mounted twin wire line and coplanar long slot element at their respective probe points. 
   The SMDs and the resulting phase shifter circuits may be relatively small in comparison to the dimension of the gap across the UHF long slot  54 - 3 . As a result the phase shifter and balun circuitries may be placed across a portion of the gap, as depicted diagrammatically in  FIG. 10 , on one side at the long slot probe point while running a trace  54 - 3 A to the side of the gap to excite the voltage potential across the gap at the probe point to generate the radiating fields. 
   The DC bias circuits for the varactor and PIN diodes, and the signal and control lines to the phase shifter circuits are not shown in  FIG. 9 . In an exemplary embodiment, the signal and control lines may be buried within the multilayer RF flex circuit board and routed to the surface via plated through holes. 
     FIG. 11  is a schematic diagram of an exemplary embodiment of X-band lens array circuitry. The X-band lens element circuitry may include microstrip transmission line components  54 - 20 , varactor diodes  54 - 21 , a PIN diode  54 - 22  and DC blocking capacitors  54 - 23 . These components may be used to make up flared dipole baluns  54 - 25  and switched varactor diode reflection phase shifter circuit  54 - 26 . The varactor diodes may be used in branchline coupler circuits  54 - 24 . As shown in  FIG. 11 , the reflection phase shifter circuit  54 - 26  employs a set of microstrip 3 dB branchline quadrature couplers  54 - 24  whose outputs are terminated with the varactor diodes  54 - 21 . The shift in reflection phase off the diode termination is the result of changing the capacitance of the varactor, as the bias voltage is varied across the varactor. Other quadrature coupler configuration may alternatively be used. 
   In an exemplary embodiment, a PIN diode  54 - 22  serves as a shunt switch in the center of the phase shifter circuit  54 - 26 . The balun circuit  54 - 25  includes a microstrip 0 degree/180 degree power divider with transmission line transformers to provide impedance matching and transmission line mode conversion from microstrip line to coupled microstrip on the RF flexible circuit board to the orthogonally mounted coplanar strips transmission lines that feed the dipoles. Other balun configurations may alternatively be used. 
   In an exemplary embodiment, to ensure adequate fit of the microstrip phase shifter circuitry within the X-band lattice, half of the phase shifter circuit  54 - 26  may be mounted on the surface of the RF flexible circuit board (substrate  54 - 2 ) with the radiating dipole elements  54 - 9  while the other half is mounted on the opposite surface of the RF flexible circuit board with the pick-up dipole elements  54 - 8 . The PIN diode shunt switch  54 - 22  may be mounted on the RF flexible circuit board surface  54 - 27  facing the pick-up elements  54 - 8 . The RF connections between the two phase shifter circuit halves may be accomplished using a set of plated through holes configured in the form of a caged coaxial interconnect line  54 - 30 , illustrated in FIGS.  12  and  12 A- 12 C. The interconnect line  54 - 30  includes an input microstrip conductor line  54 - 31  having a terminal end  54 - 31 A which is connected to a plated via  54 - 32  extending through the substrate  54 - 2 . A pattern of surrounding ground vias and pads  54 - 33  and connection pattern  54 - 34  provides a caged coaxial pattern pad  54 - 35 . An output microstrip conductor  54 - 36  had a terminal end connected to the plated via  54 - 32  on the opposite side of the substrate, and a pattern of surrounding pads and connection pattern  54 - 37 ,  54 - 38  is formed. Spaced microstrip ground planes  54 - 39  and  54 - 40  are formed in buried layers of the substrate  54 - 2 . 
   Using a similar caged coaxial approach, a coupled microstrip on the RF flexible circuit board surface can transition to orthogonally mounted coplanar strip (CPS) transmission line as shown in FIGS.  13  and  13 A- 13 D. In this exemplary embodiment, input coupled microstrip conductor lines  54 - 51  and a surrounding connected ground plane vias and pad pattern  54 - 53  are formed on one surface of the substrate  54 - 2 . A caged twin wire line pattern  54 - 52  is formed by the plated vias and surrounding ground vias ( FIG. 13B ), thus defining a shielded twin wire line  54 - 53  as depicted in  FIG. 13C . On the opposite substrate surface, coplanar strips  54 - 55  with an orthogonal H-plane bend are connected to the twin leads to form an electrical RF connection to the dipole  54 - 8 . Microstrip groundplanes  54 - 56 ,  54 - 57  are disposed in a buried layer within the substrate and on a surface of the substrate. Note that the DC biased circuits and the signal and control lines to the phase shifter circuits are not shown. The signal and control lines may be buried within the multilayer RF flexible circuit board and routed to the surface via plated through holes. 
   Aspects of embodiments of the disclosed subject matter may include one or more of the following: 
   The use of a space feed to reduce RF loss and feed complexity to power a large number, e.g. in one exemplary embodiment, 4 million, X-band radiating elements. 
   Interleaving of UHF and X-band radiating elements over the same aperture. 
   Dual band operation over X band and UHF bands, with the frequency ratio 20:1 for X and UHF. 
   Application of long slot elements to accommodate shared aperture. 
   Exploitation of polarization twist to isolate high band, low band, and between the pick-up side and the radiating side of the lens array. 
   Use of feed-through and reflective modes to cover both forward and backward directions. 
   Although the foregoing has been a description and illustration of specific embodiments of the subject matter, various modifications and changes thereto can be made by persons skilled in the art without departing from the scope and spirit of the subject matter as defined by the following claims.