Abstract:
The replacement and elimination of duplexers in a tightly coupled dipole phased array starts with transmit and receive functions physically separated and having different antenna port feeds. The simple coupling network used with tightly coupled dipole arrays is replaced by a state switch which alternates between a coupling state and a dipole feed connection state. The basic method can be applied to antenna apertures of various kinds, including both linear and dual polarized versions. The ability to locate state switches at various nodes in tightly coupled dipole phased arrays permits flexibility in antenna design and eliminates bulky and lossy components, simplifies the design requirements and allows independent optimization of the components.

Description:
RELATED APPLICATIONS 
       [0001]    This Application claims rights under 35 USC §119(e) from U.S. Application Ser. No. 61/328,693 filed Apr. 28, 2010, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to closely or tightly coupled dipole arrays and more particularly to a method and apparatus for elimination of duplexers in transmit/receive phased array antennas. 
       BACKGROUND OF THE INVENTION 
       [0003]    As illustrated in U.S. Pat. No. 6,512,487 entitled Wide Band Phased Array Antenna and Associated Methods; U.S. Pat. No. 6,771,221 entitled Enhanced Bandwidth Dual Layer Current Sheet Antenna; U.S. Pat. No. 7,084,827 entitled Phased Array Antenna with an Impedance Matching Layer and Associated Methods; as well as U.S. Pat. No. 6,552,687 entitled Enhanced Bandwidth Single Layer Current Sheet Antenna, arrays of closely or tightly coupled dipole arrays are described. These inventions are based on an invention by Benedict A. Munk described in U.S. Pat. No. 4,125,841 entitled Space Filter. It is reported that it was Munk&#39;s invention to add a coupling element at the end of each half wavelength dipole to allow the phased array to be exceedingly broadbanded. 
         [0004]    It is noted that the dipole itself is capable of an octave bandwidth, whereas derivative antennas approach a decade of bandwidth assuming the appropriate kind of coupling design between the dipoles. Moreover, planar two dimensional arrays of a sheet of dipoles increase gain or directivity; and by adding coupling in orthogonal directions one can also achieve multiple polarizations for the phased array. 
         [0005]    Applications for such planar phased arrays are in general for broadband surveillance, electronic warfare applications and any applications which require very broadband phased arrays. 
         [0006]    When utilizing such closely coupled dipole arrays for transmit/receive operations, it is common to provide either a circulator or a double pole, double-throw transmit/receive switch at each of the feeds of the dipoles in order to isolate the transmitter from the receiver and vice versa. The circulators and transmit/receive switches are in general referred to as duplexers. However, when it is intended for these antennas to be driven in the transmit and receive modes alternately, placing a circulator or transmit/receive switch at each of the antenna feeds for the dipoles can be physically impossible, depending on frequency of operation, due to the limitations of the physical size of such circulators and switches which precludes their use above the ground plane normally used for such planar arrays. 
         [0007]    For instance, circulators tend to be too large at the frequencies of interest. This is because the spacing between the electronics is approximately one half wavelength at the operating frequency. Note that at the highest frequency for which the antenna will operate, the spacing between the elements needs to be no more than one half wavelength at this frequency. Duplexers in the form of circulators and T/R switches are much too large to be placed at the feedpoint of a dipole, especially when these duplexing units are above the ground plane for the planar array. Moreover, the typical circulators are bandwidth-limited and TR switches have excessive losses. Thus T/R switches absorb power during the transmission process and limit sensitivity on the receive side. It will be appreciated that for a decade bandwidth switch there could be as much as a dB loss or even more if high power switches are used. Note also that any piece of electronics that is interposed between the receiver or transmitter and the antenna will have parasitics that will limit the bandwidth. 
         [0008]    In summary, circulators have limited bandwidth, limited usually to an octave. Moreover, circulators get bulkier and lossier as one seeks to achieve a 5:1 bandwidth. Thus, using a circulator limits the bandwidth performance. On the other hand, transmit/receive switches with pin diodes result in unacceptable losses that limit performance. Moreover, dipoles require balanced inputs and the use of baluns to convert an unbalanced line to a balanced line is undesirable due to the added parasitics and losses. 
         [0009]    Two other factors which further complicate phased array implementations of circulators include the use of high field strength bias magnets which must be shielded to prevent interaction with the shielding significantly adding to the bulk of the structure. 
         [0010]    Finally as mentioned above, balanced lines require baluns which are differential single ended to balanced devices required between the feed and the circulator, or the feed and the transmit receive switch. The use of baluns adds additional circuitry which further degrades performance in terms of loss, match and bandwidth. 
         [0011]    Such weight and size limitations as well as limitations on performance are particularly acute when, for instance, planar arrays of miniature dipoles exceed 1,000×1,000 dipole arrays or greater. While it is theoretically possible to locate the duplexing circuitry beneath the ground plane of the antenna, it is highly desirable to be able to eliminate duplexers so as to be able to fabricate reasonable size and planar arrays, with the antenna elements existing above the ground plane. In short, there is a need to eliminate the large amount of electronics directly connected at the feed of these antennas when contemplating transmit/receive functions. 
       SUMMARY OF INVENTION 
       [0012]    It is part of the subject invention to replace or eliminate the duplexers in a tightly coupled dipole phased array by recognizing that it is possible to separate the transmit and receive functions by locating a state switch either at the normal feedpoint of a dipole or between the ends of adjacent dipoles that would normally carry a capacitance coupling. The state switch alternates between a coupling state and a dipole feed connection state such that in a transmitting state a state switch is activated for direct feed across opposed quarter wave dipole elements, whereas in a receive state coupling elements are switched across adjacent dipole ends. 
         [0013]    By connecting transmit elements and receive elements between successive quarter wave dipole elements in a line of dipoles and by appropriate switching of the state switches one can configure the antenna array for either a transmit mode or a receive mode, with the transmit element, the receive element and appropriate state switches switched in accordance with the receive or transmit mode required. 
         [0014]    In one embodiment, the dipoles are interleaved such that dipoles are fed through a state switch at a dipole feedpoint and are provided with capacitive coupling through a state switch at another point, namely between opposed dipole ends. Thus in the transmit mode the state switch at one point is switched to act as a direct feed to the feedpoint of a dipole, whereas in the receive state, a state switch at an adjacent point switches a capacitive element across adjacent dipole ends. 
         [0015]    The result is that one can provide minimal electronics at the feedpoints of the dipole or adjacent dipole ends above the ground plane such that one can have very large numbers of transmit/receive elements in a planar array and switch the array between transmit and receive modes without the use of duplexers, either in the form of circulators or DPDT T/R switches. Moreover, state switches employ minimal electronics making them deployable at the spaced-apart ends of opposed λ/4 dipole elements. Thus, the present invention eliminates the need to have either a circulator or a transmit/receive switch at a dipole feed by separating the points at which one places the transmit and receive elements. No longer is the dipole feedpoint used for both transmit and receive functions. 
         [0016]    Key to this is the understanding that one can feed the antenna at places where a capacitive coupling originally was coupled between the ends of adjacent dipoles. Normally it was thought that dipoles could only be fed at a single feed point. However, in planar arrays of dipoles, adjacent quarter wave dipole elements exist not only at what was traditionally thought of as the feedpoint, but also at the ends of adjacent dipoles. 
         [0017]    As a result of locating state switches at various points one has achieved considerable flexibility since one can separate out the transmit and receive functions by simply distributing the transmit and receive elements and controlling associated state switches. 
         [0018]    What is happening is that one has an array of transmitter and receiver antennas in which in one instance the receiver uses one pair of quarter wave dipole elements, but in the transmit sequence one uses a different pair of quarter wave dipole elements. It will thus be appreciated that the same quarter wave dipole element may serve in one instance as part of a transmit antenna and in the alternate mode as part of a receive antenna. 
         [0019]    In one embodiment, the state switch includes a pair of single-pole double-throw switches which are coupled between opposed quarter wave dipole elements and then are switched either towards the pair of electronic inputs or towards a coupling impedance that places a coupling impedance between the dipole elements. Thus one is switching the coupling impedance in and out, or one is switching the direct feed to the transmitter in and out. 
         [0020]    Note that the state switch is simpler than the kind of transmit/receive switches that in general involve a double-pole double-throw switch. Having a pair of single-pole double-throw switches involves half of the complexity of a double-pole double-throw switch. Note that for a double-pole double-throw switch one would need four single-pole single-throw switches, whereas in the subject case one only utilizes two single-pole double-throw switches. Having half the complexity results in half of the parasitics and half of the losses, as well as half of the bandwidth restriction as compared with the standard double-pole double-throw switch. Thus, the subject state switch has one half the total impact of a double-pole double-throw switch. 
         [0021]    In summary, the replacement and elimination of duplexers in a tightly coupled dipole phased array starts with transmit and receive functions physically separated and having different antenna port feeds. The simple coupling network used with tightly coupled dipole arrays is replaced by a state switch which alternates between a coupling state and a dipole feed connection state. The basic method can be applied to antenna apertures of various kinds, including both linear and dual polarized versions. The ability to locate state switches at various nodes in tightly coupled dipole phased arrays permits flexibility in antenna design and eliminates bulky and lossy components, simplifies the design requirements and allows independent optimization of the components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    These and other features of the subject invention will be better understood in connection with the Detailed Description, in conjunction with the Drawings, of which: 
           [0023]      FIG. 1  is a prior art description of the mounting of a planar array on a vehicle illustrating a TX/RX controller coupled to the planar array; 
           [0024]      FIG. 2  is a diagrammatic illustration of the planar array of  FIG. 1  illustrating linear arrays of dipoles; 
           [0025]      FIG. 3  is an expanded view of a portion of the array of  FIG. 2  illustrating individual dipoles having the ends thereof capacitively coupled together; 
           [0026]      FIG. 4  is a diagrammatic illustration of a prior art system for connecting to the dipoles of  FIG. 3  in which a circulator is utilized to separate out the signals from a transmitter to the dipole and receive signals from the dipole; 
           [0027]      FIG. 5  is a prior art illustration of the utilization of a double-pole double-throw switch as a transmit/receive switch between a transmitter and a receiver coupled to a dipole of  FIG. 3 ; 
           [0028]      FIG. 6  is a diagrammatic illustration of a balanced to balanced double-pole double-throw switch for utilization of the transmit/receive switch of  FIG. 5 ; 
           [0029]      FIG. 7  is a diagrammatic illustration of the utilization of a state switch between quarter wave dipole elements of a linear array of dipoles in which state switches are controlled to couple a capacitance element between opposed ends of the dipoles or to couple feed lines between quarter wave dipole elements, with transmit and receive elements being switched by the control unit, also showing the interleaved dipole structure in which dipoles overlap to share a common quarter wave element; 
           [0030]      FIG. 8A  is a diagrammatic illustration of a portion of the array of  FIG. 7  in which a receive element is on and a transmit element is off, indicating a direct connection of the receive element to adjacent quarter wave dipole elements and a capacitive element across different adjacent quarter wave elements; 
           [0031]      FIG. 8B  is a diagrammatic illustration of the array of  FIG. 7  in which a receive element is off and a transmit element is on; 
           [0032]      FIG. 9  is a diagrammatic illustration of one embodiment of a state switch in which pair of single-pole double-throw switches is utilized which alternately couple the antenna inputs to feed the dipole elements or couple a capacitive element across opposed dipole elements; 
           [0033]      FIGS. 10A ,  10 B and  10 C are diagrammatic illustrations of the physical layout of the state switches between opposed quarter wave dipole ends schematically showing the circuit within a state switch and the conductors extending from tabs on the state switch through the substrate and ground plane that carry both balanced RF and DC signals for controlling the state of the associated state switch; 
           [0034]      FIG. 11  is a diagrammatic illustration of a prior art planar array in which elements are connected both in the horizontal and the vertical directions; 
           [0035]      FIG. 12  is a diagrammatic illustration of a portion of the planar array of  FIG. 10  illustrating the quad feed of connection of adjacent crossed dipole elements at their respective ends; 
           [0036]      FIG. 13 , left, is a diagrammatic illustration of the basic approach of  FIG. 12  which requires complex quad feeds at the crossover elements, whereas the subject invention,  FIG. 13  right, moves the vertical polarization feed or the horizontal polarization feed to opposed ends of quarter wave dipole elements and restricts the crossover coupling to a capacitive feed, thus reducing feed complexity; 
           [0037]      FIG. 14  is a diagrammatic illustration of the complex quad feed of  FIG. 13  indicating the requirement of four feed lines to opposed ends of the crossed dipole elements, with opposing feeds paired and adjacent feeds separated to show separation between the horizontal and vertical polarizations; 
           [0038]      FIG. 15  is a diagrammatic illustration of the crossed elements of an XY array of the subject invention in which only coupling elements need be attached across crossed dipole ends; 
           [0039]      FIG. 16  is a diagrammatic illustration for transmit/receive arrays in which the transmit feeds are simple balanced state feeds, as described previously, and only the receive elements are quad fed, state switching for the low power receive being easier to implement than transmit; 
           [0040]      FIG. 17  is a schematic diagram for the state switch of the quad fed receive connection of the array in  FIG. 16 ; 
           [0041]      FIG. 18  shows a full T/R array in which the dipole elements are connected through a state switch configuration having a T or R connection in one direction and a coupling connection in the orthogonal direction, the lines inside the box indicating the direction of the connection for T or R, noting quad penetrations of the ground plane are required; 
           [0042]      FIG. 19  shows the state switch, including coupling connection, for the array in  FIG. 18 ; 
           [0043]      FIG. 20  shows an array in which a unit cell can be configured using the state switches to represent one frequency in a transmit mode and double the frequency in a receive mode; 
           [0044]      FIG. 21  is a unit cell for the multi-frequency array of  FIG. 20 . 
           [0045]      FIG. 22  is a schematic diagram of a modified state switch for use in the receive feed in dual frequency arrays; and, 
           [0046]      FIG. 23  is a schematic diagram of three equivalent configurations of the quad-connected coupling connection of  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    As shown in U.S. Pat. No. 6,512,487, a wideband phased array antenna  10  is mounted to the nose cone of an aircraft  12  or other rigid mounting member having a non-planar three dimensional shape. As shown, the array is connected to a transmit/receive controller  14  for alternately driving the antenna or receiving signals. 
         [0048]    This array is a closely or tightly coupled dipole array such that as shown in  FIG. 2  there is a dipole layer  20  which in one embodiment is comprised of a conductive layer having an array of dipole elements printed thereon. As can be seen by the exploded view of  FIG. 3  each of the dipole elements  40  includes a feed  42  between adjacent dipole ends  44 . 
         [0049]    As shown in  FIG. 4 , the array requires isolation of the transmitter from the receiver. Here, dipole elements  44  are connected to a circulator  46  which couples transmit element  48  to dipole  44  during a transmit mode, and receive element  50  to the dipole elements during a receive mode. This constitutes one embodiment of a duplexer which protects the receiver from outgoing energy coupled to the dipole during the transmit mode and which isolates the transmitter from the receiver during the receive mode. 
         [0050]    Referring to  FIG. 5 , the duplexer may be alternatively configured as a double-pole double-throw switch  52  coupled between dipole elements  44  and transmitter element  48  and receiver element  50  to provide the same function as the circulator of  FIG. 4 . 
         [0051]    As to the configuration of the transmit/receive switch  52 , typically as shown in  FIG. 6  switch  52  is a balanced to balanced double-pole to double-throw switch which, inter alia, may include baluns so that unbalanced lines may be connected to the dipole antenna which has typically a balanced feed. 
         [0052]    More particularly, for an array configured for combined transmit and receive (T/R) operation, a duplexer is added at the antenna feed to separate the transmitter from the receiver. The circulator is the most commonly used form of the duplexer, whose purpose is to separate the transmit and receive paths from each other at the antenna connection, as well as to provide isolation and reduce unwanted reflections and interactions among the components. 
         [0053]    The circulator for a wide bandwidth phased array is a bottle neck to system design and performance. Typically for a circulator it is possible to get extremely good performance over less than an octave bandwidth. For a circulator moderately good performance with 10 dB of return loss and 15 dB of isolation can be achieved at up to about 3:1 bandwidth. Bandwidths of 10:1 are not feasible with available circulator technology. 
         [0054]    Two other factors further complicate phased array implementations of circulators. First, bias magnets of sufficiently high field strength must be shielded from each other. This significantly adds to the bulk of the structure. Moreover, broadband phased arrays tend to be comprised of elements that have differential (balanced) feeds. Either pairs of circulators would be required at each antenna element feed, or a broad bandwidth balun component is needed between the feed and the circulator. This additional circuitry further degrades the performance of the antenna in terms of loss, match, and bandwidth. 
         [0055]    Clearly some alternate implementation is required for the wideband duplexer. Y. Ayasli, “Field Effect Transistor Circulators,” 1989 IEEE Trans. On Magn., vol. 25, pp. 3242-3247, the contents of which are incorporated herein by reference, and others have described methodologies for active circulators using microwave transistors and exploiting the unilateral property of transistors. That is they have gain from input to output but attenuate signals from the output to the input. Care must be taken to assure stability of these circuits. Unfortunately active circulators tend to generate excess noise, limiting input sensitivity, while also limiting the output power in the transmit arm. Methods that rely on frequency conversion, using optical or other techniques, have the additional limitation on dynamic range due to nonlinearities in the up and down conversion. 
         [0056]    Note, any non-balanced or single ended duplexer solution would require a broad band balun to connect to the antenna. Typical microwave baluns operate over 3:1 bandwidths, with decade bandwidths also feasible as described in D. Meharry, “Decade Bandwidth Planar MMIC Balun,” IEEE MTT-S Digest, 2006, the contents of which are incorporated herein by reference. However, baluns add losses and are limited in their ability to present good match over a very wide bandwidth. 
         [0057]    Balanced antenna elements with balanced (differential) electronics may be the best way to achieve good performance over very broad bandwidths. This conceptually involves a double-pole double-throw switch. However, this approach still has limitations. Primarily this is because of the complexity of the circulator that has to be positioned at a single small location. The transmit and receive connections are by necessity very close to each other, creating potential issues with isolation. Furthermore, it is difficult to maintain symmetry and balance in the overlapping interconnections. Finally, the actual receive and transmit electronics connections will have to be moved further away from the antenna interface to allow for the space to package the individual receive and transmit components. All of these factors increase complexity and make it more difficult to achieve bandwidth match over the entire bandwidth. 
         [0058]    The requirement of a duplexer connected between a balanced antenna and the receive and transmit ports of the system translates into a high degree of microwave complexity in a very confined space at the antenna feed. An additional requirement of dual polarization will more than double the associated complexity. It may also require twisting or other complications of the interconnection scheme. Parasitic effects of the microwave junctions compound the difficulties of achieving a high degree of match over extended bandwidths, at the same time having a direct impact on transmit power and efficiency and on receive sensitivity and dynamic range. This situation is also complicated by the need to remove the heat generated in this confined space. 
         [0059]    Referring to  FIG. 7 , in the subject invention state switches  60  are positioned across the ends of opposed quarter wave dipole elements  62 . Switches  60  alternately connect the opposed ends of the dipole elements to transmitter or receive elements or capacitively couple the opposed ends together. In  FIG. 7  the receive elements  64  are turned on, whereas the transmit elements  66  are turned off, thus to provide the array with a receive function. In this configuration in each of the state switches  60 , arrows point in the direction of the connection between adjacent dipole elements  62 . In this case a receive element  64 ′ is coupled to a state switch  60 ′ such that the state switch couples the receive element to opposed quarter wave dipole ends  68 ′, with distal end  70 ′ of dipole element  62  being capacitively coupled to opposed dipole end  72 ′ through capacitive coupling element  74 ′ in a state switch  60 ″. 
         [0060]    It will be appreciated that each of the state switches is interposed between opposed quarter wave dipole element ends and function either to connect the opposed dipole element ends directly to the transmit element, or to capacitively interconnect the opposed dipole ends. 
         [0061]    As seen, the state elements are under control of a transmit/receive control unit  80  so as to control the state of the state switches such that successive state switches have opposite switching configurations. 
         [0062]    As shown, this means that in the receive mode state switch  60 ′ couples the receive element directly to the associated quarter wave dipole elements, whereas successive state switch  60 ″ interconnects the adjacent dipole ends through an impedance, such as a capacitor. 
         [0063]    It is also noted that transmit/receive control unit  80  is simultaneously coupled to control the transmit element on/off mode for the transmit elements and the receive elements on/off mode for the receive elements. 
         [0064]    Here it can be seen that in the receive mode depicted dipole elements  62 ′ are capacitively coupled together and receive element  64  is turned on. Alternatively in a transmit mode in which transmit element  66  is turned on, transmit element  66  is directly coupled to a dipole comprised of dipole element  62 ′ and dipole element  62 ″ such that the overall length of the dipole  62 ′,  62 ″ is again a half wavelength, λ/2. Here it can be seen that there is an interleaved structure in which in the receive mode dipole element  62 ′ is used with one set of dipole elements in the receive mode, whereas the same dipole element  62 ′ is utilized with another set of dipole elements in the transmit mode. 
         [0065]    More particularly and referring now to  FIG. 8A  in the receive mode in which receive element  64 ′ is turned on, state switch  60 ′ couples the receive element directly to quarter wave dipole elements  62 ′ and  62 ″. At the same time transmit element  64 ″ is turned off and is disconnected from the dipole pair  62 ′ and  62 ″. In this case state switch  60 ′ connects a capacitive element  74 ′ across adjacent dipole element ends. 
         [0066]    Referring to  FIG. 8B , in this transmit embodiment the transmit element  66 ′ is turned on and receive element  64 ′ is turned off. Here the transmit element is directly coupled to element  62 ″′ and element  62 ′ through state switch  60 ″′, whereas state switch  60 ″ now completely disconnects receive element  64 ′ from the associated dipole elements and rather connects capacitive element  74 ′ across the associated opposed dipole ends. 
         [0067]    Referring now to  FIG. 9 , state switch  60  rather than having a double-pole double-throw T/R switch configuration is comprised instead of single-pole double-throw switches  80  and  82  which in one mode connect antenna input  84  to dipole elements  86  and  88 . 
         [0068]    Alternatively, single-pole double-throw switches  80  and  82  connect a coupling element  90  across dipole elements  86  and  88 . 
         [0069]    It will be appreciated that the electronic complexity of the solid state switch is at least half that associated with a double-pole double-throw switch configuration common for TR switches. Also note that there are no baluns involved in connecting the antenna input to the dipole. 
         [0070]    Thus, when using the tightly coupled dipole array to totally eliminate the duplexer by separating the receive and transmit connection points to the array, this creates interleaved transmit and receive arrays which are offset from each other by a quarter wavelength. 
         [0071]    Referring now to  FIGS. 10A ,  10 B and  10 C, as to the physical configuration of the dipoles and the associated state switches, as can be seen from  FIG. 10A , adjacent quarter wave dipole segments  100 ,  102  and  104  are located on a planar surface  106  which is situated above the ground plane  101 , with state switches  108  and  110  coupled across adjacent quarter wave dipole element ends as illustrated. 
         [0072]    Each of the state switches carries tabs  112  coupled through conductors  113  through the mounting surface and through any ground plane  101 . These conductors are connected, for instance to T/R control unit  80  of  FIG. 7  and to respective transmit or receive elements. 
         [0073]    It will be seen that the state switches are spaced sequentially along the dipole elements with a λ/4 spacing. 
         [0074]    Referring to  FIG. 10B , in a transmit mode, tabs  112  of state switch  108  are connected by internal single-pole double-throw switches  114  to respective quarter wave dipole elements  100  and  102 . State switch  110  has its single-pole double-throw switches  116  connected so that a capacitor  118  is connected between quarter wave dipole elements  102  and  104 . 
         [0075]    Referring to  FIG. 10C , in a receive mode, state switch  108  utilizes switches  114  to connect quarter wave dipole elements  100  and  102  through a capacitor  120 , whereas state switch  110  has switches  116  configured to couple tabs  112  to respective to quarter wave dipole elements  102  and  104 . 
         [0076]    It is noted that direct RF connection to dipole ends is through tabs  112 , whereas the capacitive coupling between dipole ends does not require connection below the ground plane. However, DC control signals are impressed on conductors  113  to couple the DC control signals to respective state switches. 
         [0077]    Note that RF signals are coupled through conductors  113  when it is required that the state switch connect the associated dipole either to a transmitting element or a receiving element. 
         [0078]    More particularly, for a receive only array referring back to  FIG. 7 , the dipole coupling is replaced with a switching element that alternates between a coupling state and a feed state. In this manner, a feed for a transmit port can be placed at the location of the coupling element in a receive only array. The feed for the receive element has also been replaced by a state switch. The configuration shows the connection for a receive state. 
         [0079]    Alternating the state switch converts it to a transmit array, offset by λ/4 at the high frequency end. 
         [0080]    The differential transmit and receive amplifiers can be separately and independently optimized for desired performance levels, enabling a simpler, more effective, and higher performance overall solution. 
         [0081]    Detailed analyses have been carried out using the 3D finite element simulator (HFSS) to confirm the feasibility of switching a T/R phased array in this manner. 
       Dual Polarization and Multi-Frequency Operation 
       [0082]    Frequently it is necessary for the T/R array to also support dual polarization. A prior art array is shown in  FIGS. 11 and 12  which depict a quad feed  130  comprised of feeds  132  for the vertical (Y) polarization and feeds  134  for the horizontal (X) polarization. Here the array is comprised of dipoles  40 , with the quad feed providing for dual polarization. 
         [0083]    A complication arises from the fact that conventional configurations require a “quad-feed” arrangement where the balanced feeds associated with orthogonal polarizations are at the same point. This is shown at the left hand side of  FIG. 13 . Connecting to a quad-feed  135  is much more difficult than connecting to a linear feed point  137  on the right hand side of  FIG. 13 . Here vertical polarization and horizontal polarization feeds are at the less complicated linear feed points. 
         [0084]    As can be seen in  FIG. 14 , as to quad drive, leads are required from four opposed dipole ends  100 ,  102 ,  104  and  106  through a ground plane. Excitation of the X oriented dipole elements arises from the pairing of  102  and  106 , and excitation of the Y oriented dipole elements arises from excitation of the pairing of  100  and  104 . Any asymmetry imposed on the structure, such as that required when the leads are brought out into a planar configuration, causes unwanted coupling between the two polarizations and degrades antenna performance. As shown in  FIG. 15 , coupling between opposed dipole ends can be a simple arrangement of crossed capacitors or other coupling elements  108  and  109  connected respectively to dipole ends  100 - 104  and  102 - 106 . 
         [0085]    It is much easier to construct a “quad-coupling” as shown in  FIG. 15 , because at intermediate points  109  used in the receive mode no RF penetrations of the ground plane are needed. Here only capacitive coupling is required at normal linear array connections. The coupling can even be implemented in a fashion that completely preserves X and Y symmetry. If the coupling is via cross capacitors, sufficient isolation between the capacitors is made possible due to capacitor alignment and configuration. See also equivalent realization of the coupling connection in  FIG. 23 . Thus, by interchanging the locations of the feed and the coupling network to more convenient locations a much more workable solution is obtained. 
         [0086]    More specifically, when one has an orthogonal array of dipoles, crossed dipoles are sometimes fed from the same common point which requires four lines or conductors going to the cross point. However, if one has a transmit only or receive only array then at various points or nodes on the array one need only have capacitors at the crossovers. This requires no control lines or RF lines to the crossover point which greatly simplifies manufacturing. Thus a state switch and embedded circuitry may be positioned at the cross points, but with no control over the state switch and no RF feeds or DC control lines. In this case the state switch coupling capacitors are permanently connected across opposed ends of dipoles. Moreover, with orthogonal crossed dipole arrays one can offset the transmit and receive elements so that one only has active state switches at a non-crossover point. 
         [0087]    In an orthogonal array one of necessity has to have cross points, but one can configure the array to have only capacitive elements connected to the ends of opposed dipoles at these cross points. 
         [0088]    On the other hand, the RF feed for the orthogonal array may occur at non cross points so that the RF feed is not at a cross point but rather at a more easily accessible feed point. 
         [0089]    Note that the coupling elements do not have to have feed points so that the cross point structure may be simplified. 
         [0090]    Thus for instance for a receive only array, one can construct the electronic feeds to places where there are no cross points, i.e. at the end of opposed dipoles that do not terminate in a cross point area. Thus, at the cross point area there need not be a state switch at all. The reason for this configuration is because if one is constructing a receive only array there is no need to change states between coupling and feeding. Note also that if it is a transmit only array no state changes are required. 
         [0091]    What is done is to eliminate the need for quad feeds at cross points which is a much more complex connection scenario than providing a pair of dipole leads. 
         [0092]    Thus, two dimensional or orthogonal arrays have added complications of how everything fits together in terms of where to place the coupling and where to place the electronic feed. 
         [0093]    Most importantly, as will be seen in  FIG. 16 , transmit/receive functionality can be achieved by alternating locations of receive and transmit connection ports in the array. By appropriate placing of transmit and receive elements, one has considerable flexibility. For instance, because of the lower power handling, a quad-configuration for a receive port is easier to implement than for transmit. The transmit state switch is the same as that in  FIG. 9 . A schematic for a possible implementation of the receive state switch for the quad feed is shown in  FIG. 17 . Examination of this schematic reveals that it is simply comprised of a pair of the state switches  60  from  FIG. 9 , one for each polarization. 
         [0094]    A further option for transmit/receive operation is shown in  FIG. 18 . In this case the receive and transmit feeds are both located at a quad junction  300  of dipoles. However, there is only a single, balanced penetration of the ground plane, either for transmit or for receive. The polarization of the feed is also indicated by the horizontal or vertical line. Note that the transmit or receive connections that are in the adjacent diagonal positions are of alternate polarization. A coupling connection is also required for the dipoles situated in the orthogonal direction from the transmit or receive connection. A state switch usable for all of the feeds is shown in  FIG. 19 . Here for the transmit state switch at a dipole quad connection for a “T” feed input one has Single Pole Double Throw SPDT switches  302  and  304  as illustrated which couple dipole ends  306  and  307  respectively to either the input or a coupling impedance  310 . Here dipole ends  312  and  314  are coupled together by a coupling impedance  316 . Note, it is not necessary to switch the orthogonally connected coupling associated with dipole ends  312  and  314 . Note also that the state switch for the “R” feed is identical to that of the “T” feed shown in  FIG. 19 . 
       Multi-Frequency Operation 
       [0095]    Moreover, the ability to design an antenna structure with extended bandwidth capability offers an opportunity where either a transmit or a receive sub-array can work at half of the frequency capability of the other array. One third frequency and other configurations are a direct extension of the methods used for the one half frequency configuration. 
         [0096]    In many systems it may not be necessary for the transmit function to cover the same bandwidth as for the receive function. In this case a solution involves the number of transmit ports being half or less than the number of receive ports.  FIG. 20  depicts a case in which the receive bandwidth is twice that of the transmit bandwidth. Also shown in  FIG. 20  is a unit cell of the area, delineated by the dotted box  140 . The unit cell is a structure which can be repeated in both directions to fill the array. An expanded view of the unit cell is shown in  FIG. 21 . 
         [0097]    Referring back to  FIG. 20 , how one can distribute the transmit and receive element couplings to the array is now described. In  FIG. 20  there is a horizontal line  200 , shown connecting several feeds for the horizontal (X) feed elements. Also in line  200  and as shown in the lower part of the  FIG. 20 , as well as in  FIG. 21 , are transmit elements  202  for the horizontal orientation, crossover elements  204  containing only coupling connections, and receive elements  206  for the horizontal direction. On the other hand, in the vertical direction there are state switches and receive elements  210  for the vertical direction coupled to them. Also inside the unit cell is a transmit element  208  for the vertical direction. The lines inside the square T or R boxes refer to a connection across opposed dipole ends in the directions illustrated. 
         [0098]    As seen in  FIG. 20 , arrays can be manufactured with different available bandwidths for the transmit and receive functions. In this case one can see that there are a number of receive elements inside the dotted unit cell  140 , noting that there are four times as many receive elements as transmit elements. This corresponds to the receive spacing being one half as great as the transmit spacing. Thus, a phased receive array can operate at twice the frequency range of a phased transmit array. 
         [0099]    The above has to do with the repeat size of the antenna. Inside the unit box would be for instance two of the receive repeats as opposed to the one for the transmit mode in each direction. 
         [0100]    The schematic for the state switch configuration of the transmit connection in this case is the same as in  FIG. 19 . Here the corresponding state switch for the receive connection is shown in  FIG. 22  in which SPDT switches  302  and  304  coupled to the “R” feed input and dipole ends  307  and  308 . Note that there is no coupling connection, but rather a straight through connection for the transmit state such that dipole end  307  is directly coupled to dipole end  308  utilizing a through connection  320 . This connects the segments of the longer dipole required for transmit operation. The quad coupling connection is the same as in  FIG. 15 , and  FIG. 23  shows three equivalent representations  330 ,  340  and  350 . 
         [0101]    Referring back to  FIG. 20 , if one goes across on line  200 , one sees two receive feeds which are spaced λ R /2 in width and a transmit feed spacing which is λ T /2 in width, that is twice as long as λ R /2 What this width represents is a box where λ R /2 represents the highest frequency of the receive dipole of the phased array. Since the transmit portion operates at an effective bandwidth of (2) λ/2 it corresponds to half the bandwidth of the receive array. What will be appreciated is that the effective λ/2 bandwidth for the receive array is one half the λ/2 bandwidth for the transmit array, such that there are four times as many receive elements in a given unit box than transmit elements. Thus, one can listen for twice the frequency bandwidth as compared to that associated with the transmit array. 
         [0102]    Moreover, as can be seen from  FIGS. 20 and 21  the receive mode requires no terminations in cross polarization positions. As illustrated a unit cell (based on the transmit function) is shown with a dashed box  140 . Note that other array combinations are possible, such as dual band receive or dual band transmit. 
         [0103]    All of the above configurations share a common feature. All of the port connections are balanced. By using differential transmit and receive amplifiers directly connected to the antenna feed or interface, baluns and other performance restricting components can be eliminated. Such amplifiers have been used in both receive and transmit programs, and can leverage an approach described in D. Meharry, “Wideband Differential Amplifier Including Single-ended Amplifiers Coupled to a Four-port Transformer,” U.S. patent application Ser. No. 12/564,791, filed Sep. 22, 2009, the contents of which are incorporated herein by reference. 
         [0104]    While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.