Patent Publication Number: US-2022239012-A1

Title: Enhanced directivity feed and feed array

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application for patent is a Continuation of U.S. patent application Ser. No. 16/924,930 filed Jul. 9, 2022, which is a Continuation-in-Part application of U.S. patent application Ser. No. 16/404,578 filed May 6, 2019, which is a Continuation application of U.S. patent application Ser. No. 15/806,181 filed Nov. 7, 2017, which is a Continuation of U.S. patent application Ser. No. 14/633,427 filed Feb. 27, 2015, the content of each of which are incorporated herein by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     Satellite antennas using reflectors for gain and multiple feeds in the configuration of single-feed-per-beam (SFPB) or multiple-feeds-per-beam (MFPB) to produce contiguous spot beam patterns or area coverage patterns have a limitation in which the feed aperture area can be insufficient to illuminate the reflector efficiently. In general, the spillover energy may exceed the optimum value that can be achieved by a single feed sized to provide a net optimum efficiency. In other words, the reflector aperture can be over illuminated and the energy radiated by the feed spilling past the reflector boundary can be greater than the optimum for net efficiency. 
     The over illumination condition can exist over the practical ranges of focal length values, and generally applies to single reflector optics and to dual-reflector optics. The over illumination condition exists for transmission type convergent optics (e.g., lens) as well as reflector convergent optics. Convergent optics captures radio frequency (RF) energy over a defined area and redirects the energy to a smaller area. The over illumination condition can occur for defocused or focused positions of feeds arranged in a contiguous manner to form contiguous spot beams with reasonable gain loss at the secondary pattern two-beam and three-beam cross-over locations. A similar over illumination condition may arise in the case of an MFPB configuration, where the reflector or lens feeds are defocused to configure a phased array fed reflector antenna. 
     An approach in SFPB spot beam satellite system applications to improve the illumination uses multiple reflectors for a congruent coverage area and assigns near focused feeds to reflectors in a manner to avoid having contiguous coverage beams within a single reflector. 
     Another solution uses feed clusters (e.g., 3, 7, 13 elements) and relatively complex orthogonal waveguide beamforming networks to provide overlapping excitation of adjacent feeds to form each beam. 
     Mitigation examples exist for the over-illumination condition, in which the modes within a feed horn are controlled in an attempt to produce a near uniform amplitude distribution at the horn aperture. In these mode control examples, the near uniform amplitude distribution can be an approximation to the TEM mode in the feed horn structure. Another mitigation example maximizes the feed aperture area in a triangular feed lattice and uses horns having a hexagonal shaped boundary. Neither of these configurations provides optimum illumination conditions and may exhibit only marginal performance improvements over the more common geometry limited configurations. 
     SUMMARY 
     In accordance with the present disclosure, an antenna may include a reflector and an array of feeds. Each feed in the array may include a horn having a multi-flare mode conversion section having several flare angles. Each feed may include a dielectric insert having a portion that extends through a part of the multi-flare mode conversion section and a portion that extends beyond an aperture of the multi-flare mode conversion section. 
     The following detailed description and accompanying drawings provide a better understanding of the nature and advantages of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With respect to the discussion to follow and in particular to the drawings, it is stressed that the particulars shown represent examples for purposes of illustrative discussion, and are presented in the cause of providing a description of principles and conceptual aspects of the present disclosure. In this regard, no attempt is made to show implementation details beyond what is needed for a fundamental understanding of the present disclosure. The discussion to follow, in conjunction with the drawings, make apparent to those of skill in the art how embodiments in accordance with the present disclosure may be practiced. In the accompanying drawings: 
         FIG. 1  is a block diagram of a satellite communication system that can be improved by various embodiments of the present disclosure. 
         FIG. 1A  shows some details of a reflector antenna for satellite  105  depicted in  FIG. 1 . 
         FIG. 2  is an isometric view of a feed assembly in accordance with an illustrative embodiment of the present disclosure. 
         FIG. 3  is an exploded view of the feed assembly illustrated in  FIG. 2 . 
         FIG. 3A  is a cross-sectional view of the feed assembly illustrated in  FIG. 2 . 
         FIGS. 4 and 4A  illustrate, respectively, an isometric view and a cross sectional view of an illustrative embodiment of a horn in accordance with the present disclosure. 
         FIG. 5  shows another illustrative embodiment of a horn in accordance with the present disclosure. 
         FIGS. 6A, 6B, 6C, and 6D  illustrate various embodiments of a dielectric insert in accordance with the present disclosure. 
         FIG. 7  shows a magnified portion of the cross-sectional view shown in  FIG. 3A . 
         FIG. 8  is an isometric view of a feed assembly in accordance with another embodiment of the present disclosure. 
         FIG. 8A  is a hidden line view of the feed assembly illustrated in  FIG. 8 . 
         FIGS. 9 and 9A  illustrate, respectively, an isometric view and a hidden line view of a diplexer-polarizer. 
         FIGS. 9B and 9C  illustrate, respectively, an isometric view and a top view of another embodiment of a diplexer-polarizer. 
         FIG. 10  illustrates an example of a feed array in accordance with the present disclosure. 
         FIG. 11  illustrates a satellite reflector antenna configured with a feed array in accordance with the present disclosure. 
         FIG. 12  illustrates an example of a design flow to design a feed in accordance with the present disclosure. 
         FIG. 13  shows a computer system in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be evident, however, to one skilled in the art that the present disclosure as expressed in the claims may include some or all of the features in these examples, alone or in combination with other features described below, and may further include modifications and equivalents of the features and concepts described herein. 
     Satellite Communication Systems 
       FIG. 1  is a diagram of an example satellite communications system  100  that may be improved by systems, methods, and devices of the present disclosure. Satellite communication system  100  includes a network  120  interfaced with one or more gateway terminals  115 . Gateway terminal  115  may be configured to communicate with one or more user terminals  130  via satellite  105 . As used herein the term “communicate” may refer to both transmitting and receiving (i.e., bidirectional communication) or may refer to either transmitting or receiving (i.e., unidirectional communication) over a particular pathway. 
     Gateway terminal  115  may be referred to herein as the hub or ground station. Gateway terminal  115  may service uplink  135  and downlink  140  to and from satellite  105 . Gateway terminal  115  may also schedule traffic to user terminals  130 . Alternatively, the scheduling may be performed in other parts of satellite communication system  100 . Although only one gateway terminal  115  is shown in  FIG. 1  to avoid over complication of the drawing, embodiments in accordance with the present disclosure may be implemented in satellite communication systems having multiple gateway terminals  115 , each of which may be coupled to each other and/or one or more networks  120 . Even in wideband satellite communication systems, the available frequency spectrum is limited. Communication links between gateway terminal  115  and satellite  105  may use the same, overlapping, or different frequencies as communication links between satellite  105  and user terminals  130 . Gateway terminal  115  may also be located remotely from user terminals  130  to enable frequency reuse. By separating the gateway terminal  115  and user terminals  130 , spot beams with common frequency bands can be geographically separated to avoid interference. 
     Network  120  may be any type of network and can include for example, the Internet, an IP network, an intranet, a wide area network (WAN), a local area network (LAN), a virtual private network (VPN), a virtual LAN (VLAN), a fiber optic network, a cable network, a public switched telephone network (PSTN), a public switched data network (PSDN), a public land mobile network, and/or any other type of network supporting communications between devices as described herein. Network  120  may include both wired and wireless connections as well as optical links. Network  120  may connect gateway terminal  115  with other gateway terminals that may be in communication with satellite  105  or with other satellites. 
     Gateway terminal  115  may be provided as an interface between network  120  and satellite  105 . Gateway terminal  115  may be configured to receive data and information directed to one or more user terminals  130 . Gateway terminal  115  may format the data and information for delivery to respective terminals  130 . Similarly gateway terminal  115  may be configured to receive signals from satellite  105  (e.g., from one or more user terminals  130 ) directed to a destination accessible via network  120 . In some embodiments, gateway terminal  115  may also format the received signals for transmission on network  120 . In some embodiments, gateway terminal  115  may use antenna  110  to transmit forward uplink signal  135  to satellite  105 . Antenna  110  may comprise a reflector with high directivity in the direction of satellite  105  and low directivity in other directions. Antenna  110  may comprise a variety of alternative configurations which include operating characteristics such as high isolation between orthogonal polarizations, high-efficiency in the operational frequency band, low noise, and the like. 
     Satellite  105  may be a geostationary satellite that is configured to receive forward uplink signals  135  from the location of antenna  110  using a reflector antenna (not shown) described in more detail below with respect to  FIG. 1A . Satellite  105  may receive the signals  135  from gateway terminal  115  and forward corresponding downlink signals  150  to one or more of user terminals  130 . The signals may be passed through a transmit reflector antenna (e.g., reflector antenna described in more detail below with respect to  FIG. 1A ) to form the transmission radiation pattern (e.g., a spot beam). Satellite  105  may operate in multiple spot beam mode, transmitting and receiving a number of narrow beams directed to different regions on the earth. This allows for segregation of user terminals  130  into various narrow beams. Alternatively, the satellite  105  may operate in wide area coverage beam mode, transmitting one or more wide area coverage beams to multiple receiving user terminals  130  simultaneously. 
     Satellite  105  may be configured as a “bent pipe” or relay satellite. In this configuration, satellite  105  may perform frequency and polarization conversion of the received carrier signals before retransmission of the signals to their destination. A spot beam may use a single carrier, i.e. one frequency, or a contiguous frequency range per beam. In various embodiments, the spot or area coverage beams may use wideband frequency spectra. A variety of physical layer transmission modulation encoding techniques may be used by satellite  105  (e.g., adaptive coding and modulation). Satellite  105  may use on-board beamforming techniques or rely on off-board (ground based) beamforming techniques. 
     Referring for a moment to  FIG. 1A , in some embodiments, a reflector antenna  106  for satellite  105  may comprise a reflector  112  and a feed assembly  114  (described in more detail below) to illuminate the reflector  112  in accordance with the present disclosure. The figure shows an offset parabolic reflector configuration. However, embodiments in accordance with the present disclosure may use other antenna configurations. In some embodiments, the reflector  112  may be parabolic as depicted in  FIG. 1A , for example. In other embodiments, the reflector  112  may have any spherical, aspherical, bi-focal, or offset concave shaped profile necessary for the generation of the desired transmission and receiving beams. In other embodiments, the reflector  112  may be used in conjunction with one or more additional reflectors in a system of reflectors. The system of reflectors may be comprised of one or more profiles such as parabolic, spherical, ellipsoidal, or shaped, and may be arranged in classical microwave optical arrangements such as Cassegrain, Gregorian, Dragonian, offset, side-fed, front-fed or similarly configured optics systems known in the art. 
     Returning to  FIG. 1 , satellite communication system  100  may use a number of network architectures consisting of space and ground segments. The space segment may include one or more satellites  105  while the ground segment may include one or more user terminals  130 , gateway terminals  115 , network operation centers (NOCs) and satellite and gateway terminal command centers. The terminals may be connected by a mesh network, a star network, or the like as would be evident to those skilled in the art. 
     Forward downlink signals  150  may be transmitted from satellite  105  to one or more user terminals  130 . User terminals  130  may receive downlink signals  150  using antennas  127 . In one embodiment, for example, antenna  127  and user terminal  130  together comprise a very small aperture terminal (VSAT), with antenna  127  measuring approximately 0.6 m in diameter and having approximately 2 W of power. In other embodiments, a variety of other types of antenna  127 , including PAFR antennas, may be used as user terminals  130  to receive downlink signals  150  from satellite  105 . Each of the user terminals  130  may comprise a single user terminal or, alternatively, may comprise a hub or router, not shown, that is coupled to multiple user terminals. Each user terminal  130  may be connected to various consumer electronics comprising, for example, computers, local area networks, Internet appliances, wireless networks, and the like. 
     In some embodiments, a multi-frequency time division multiple access (MF-TDMA) scheme may be used for upstream links  140  and  145 , allowing efficient streaming of traffic while maintaining flexibility and allocating capacity among each of the user terminals  130 . In these embodiments, a number frequency channels may be allocated statically or dynamically. A time division multiple access (TDMA) scheme may also be employed in each frequency channel. In this scheme, each frequency channel may be divided into several timeslots that can be assigned to a connection (i.e., a user terminal  130 ). In other embodiments, one or more of the upstream links  140 ,  145  may be configured using other schemes, such as frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), code division multiple access (CDMA), or any number of hybrid or other schemes known in the art. 
     User terminal  130  may transmit data and information to a network  120  destination via satellite  105 . User terminal  130  may transmit the signals by upstream link  145  to satellite  105  using antenna  127 . User terminal  130  may transmit the signals according to various physical layer transmission modulation encoding techniques, including for example, those defined with the DVB-S2, WiMAX, LTE, and DOCSIS standards. In various embodiments, the physical layer techniques may be the same for each of the links  135 ,  140 ,  145 ,  150 , or they may be different. 
     Satellite  105  may support non-processed, bent pipe architectures with one or more reflector antennas as described herein to produce multiple small spot beam patterns. The satellite  105  can include J generic pathways, each of which can be allocated as a forward pathway or a return pathway at any instant of time. Large reflectors may be illuminated by a phased array of feeds to provide the ability to make arbitrary spot and area coverage beam patterns within the constraints set by the size of the reflector and the number and placement of the feeds. Reflector antennas may be employed for both receiving uplink signals  130 ,  140 , transmitting downlink signals  140 ,  150 , or both in a full duplex mode. The beam forming networks (BFN) associated with the receive (Rx) and transmit (Tx) reflector antennas may be dynamic, allowing for quick movement of the locations of both the Tx and Rx beams. The dynamic BFN may be used to quickly hop both Tx and Rx wideband beam positions. 
     Feed Assembly 
       FIG. 2  shows an illustrative embodiment of feed assembly  114  ( FIG. 1A ) in accordance with the present disclosure. In some embodiments, the feed assembly  114  may comprise a feed  202 . The feed  202  may comprise a horn  204  and a dielectric insert  206 . The dielectric insert  206  may have a first portion (e.g.,  362 ,  FIG. 3 ) disposed within the horn  204 , and a second portion (e.g.,  362 ,  FIG. 3 ) that extends beyond an aperture  242  of the horn  204 . 
     In some embodiments, the feed assembly  114  may further comprise a waveguide  212  to guide the electromagnetic (EM) waves of a transmit signal or a received signal between a coupling flange  216  and the feed  202 . For example, the waveguide  212  may provide a transmit signal, produced by transceiver  20  (or other suitable transmitter unit) and received at an input port (e.g.,  316   a ,  FIG. 3A ) of the coupling flange  216 , to feed  202  for transmission by an antenna (e.g., reflector antenna  106 ,  FIG. 1A ). Conversely, the waveguide  212  may provide a signal received by the antenna (e.g., reflector antenna  106 ,  FIG. 1A ) to an output port (e.g.,  316   b ,  FIG. 3A ) of the coupling flange  216  to the transceiver  20  (or other suitable receiver unit). In some embodiments, the waveguide  212  may be a rectangular waveguide (e.g., a square waveguide). In other embodiments, the waveguide  212  may be a circular waveguide. In some embodiments, the waveguide  212  may be ridge loaded, and in other embodiments other waveguide configurations may be used. 
     In some embodiments, the feed assembly  114  may further comprise an adapter  214  coupled to the waveguide  212 . The adapter  214  may be a filter, a polarizer, a diplexer, or other suitable radio frequency (RF) component. In various embodiments, for example, the adapter  214  may be a four-port or two-port orthomode transducer (OMT), the adapter  214  may be a single-band or dual-band septum polarizer, and so on. In other embodiments, the adapter  214  may be a combination of a polarizer and a diplexer, the adapter  214  may be a combination of a polarizer and a filter (e.g., high pass, low pass, bandpass), and so on. 
     The coupling flange  216  may be used to mount the feed assembly  114  to a suitable structural support and/or to other antenna structures. As explained above, the coupling flange  216  may include ports (e.g.,  316   a ,  316   b ,  FIG. 3A ) that serve as an input port and an output port. 
       FIG. 3  shows an exploded view of the feed assembly  114  depicted in  FIG. 2 . In accordance with some embodiments, the horn  204  may be circular waveguide comprising a first waveguide section  342  and a second waveguide section  344  coupled to or otherwise joined to the first waveguide section  342 . The first waveguide section  342  may be a circular waveguide. The second waveguide section  344  may be referred to herein as a multi-flare mode conversion section  344 . The multi-flare mode conversion section  344  may be characterized by several different flare angles between a first end  352  and a second end  354  of the multi-flare mode conversion section  344 . 
     The dielectric insert  206  may comprise a first portion  362 , which can be disposed within the volume of the horn  204 . A second portion  364  of the dielectric insert  206  may extend beyond the aperture  242  of horn  204 . 
     The waveguide  212  may include a collar  302  configured to couple the waveguide  212  the horn  204 , for example, at the first waveguide section  342 . Locking screws  304  may secure the horn  204  and/or dielectric insert  206  to the waveguide  212 . The locking screws  304  may, for example, be made from electrically conductive material such as metal. As another example, the locking screws  304  may be made from non-conductive material. In some embodiments, the horn  204  may be fixedly attached to the first waveguide section  342  using a welding or bonding technique. In some embodiments, the horn  204  and first waveguide section  342  may be made of a single additive construction method such as electroforming or direct laser sintering or other known manufacturing processes in the art. In some embodiments, a waveguide seal  306  may be provided to block or otherwise reduce RF leakage where the horn  202  joins the waveguide  212 . In some embodiments, a secondary dielectric insert (not shown) may be installed surrounding the dielectric insert  206  to secure the dielectric insert  206  to the waveguide  212 . 
       FIG. 3A  shows a cross sectional view of the feed assembly  114  depicted in  FIG. 2 . The cross sectional view illustrates that, in some embodiments, the first portion  362  of dielectric insert  206  may extend through the multi-flare mode conversion section  344  of horn  204 . The second portion  364  may extend beyond the aperture  242  of horn  204  by a given length, L. The cross sectional view further illustrates the input port and the output port formed through the coupling flange  216 . 
       FIG. 4  shows details of horn  204  in accordance with the present disclosure. In some embodiments, the horn  204  may comprise several horn segments  412   a ,  412   b ,  412   c ,  412   d . For example, the first waveguide section  342  may comprise horn segment  412   a . The multi-flared mode conversion section  344  may comprise horn segments  412   b ,  412   c ,  412   d . It will be appreciated that either or both the first waveguide section  342  and the multi-flared mode conversion section  344  may comprise fewer or more horn segments. 
     The horn segments  412   a - 412   d  may have a circular cross section. In some embodiments, the horn segments  412   a - 412   d  may be a metal such as copper, aluminum, etc. In other embodiments, the horn segments  412   a - 412   d  may be a metal alloy such as brass, zinc alloy, etc. Each horn segment  412   a ,  412   b ,  412   c  may be joined to a respective horn segment  412   b ,  412   c ,  412   d , defining respective transitions  414   a ,  414   b ,  414   c  at the joints. Any suitable joining technique may be used to join the horn segments  412   a - 412   d , including, for example, soldering, brazing, welding, and the like. 
     In accordance with the present disclosure, a cross sectional diameter d of the horn  204  may vary along the axial length of the horn  204 , thus shaping the horn  204 . Referring to  FIG. 4A , a cross-sectional view of the horn  402  illustrates that, in some embodiments, horn segments  412   a ,  412   b ,  412   c ,  412   d  can shape the horn  204  in piece-wise fashion using a linear series of flare angle changes to vary the diameter d. The horn segments  412   a ,  412   b ,  412   c ,  412   d  may be conical frusta with respective constant flare angles (e.g., the diameter d may vary linearly in a given horn segment), or cylinders (e.g., the diameter d may remain constant in a given horn segment). For example, in the particular embodiment shown in  FIG. 4A , horn segments  412   b  and  412   d  are conical frusta configured to define respective flare angles θ 2  and θ 3  measured relative to an axis of the horn  204 . In the particular embodiment shown, horn segment  412   c  is a cylinder, having no flare (e.g., the flare angle is 0°, diameter d is constant). In the particular embodiment of  FIG. 4A , horn segment  412   a  includes a portion that is a cylinder and a portion that is a conical frustum. 
     In the particular embodiment illustrated in  FIG. 4A , the horn segments  412   a ,  412   b ,  412   d  have respective flare angles θ 1 , θ 2 , θ 3 , and horn segment  412   c  has a 0° flare angle. When the horn segments  412   a ,  412   b ,  412   c ,  412   d  are joined, the flare angle along the axial length of horn  204  varies from θ 1  to θ 2  to 0° and then to  83 , respectively, at a transition within horn segment  412   a  and at transitions  414   a ,  414   b ,  414   c . In some embodiments, the flare angles may be different from one another. In other embodiments, some of the flare angles may be the same. 
     In some embodiments, the transitions of flare angles along the axial length of the horn  204  may be smooth or gradual. For example, the transitions  414   a ,  414   b ,  414   c  illustrated in  FIG. 4A  are discrete and have sharp corners. In other embodiments, the transitions  414   a ,  414   b ,  414   c  may be rounded or smoothed out; e.g., by buffing the corners. 
     Whereas each horn segment  412   b ,  412   c ,  412   d  in  FIG. 4A  is defined by a corresponding constant flare angle, in other embodiments, the flare angle may change continuously along the axial length of the horn to provide a smooth walled horn.  FIG. 5 , for example, shows a horn  504  comprising a multi-flare mode conversion section  544  having flare angles that vary in a continuous manner along an axial length of the horn  504 . Thus, for example, the flare angle may be represented by a line tangent to each point (e.g., p 1 , p 2 , p 3 ) on a cross sectional profile of horn  504  whose angle relative to the axis of the horn  504  varies from one point to the next. Stated differently, the cross sectional diameter d of horn  504  may vary continuously along its axial length. In some embodiments, for example, the change in diameter d may be defined by one or more continuous functions. For example, a spline may be used to define the cross sectional profile of horn  504  to define a flare angle that continuously varies along the axial length of the horn  504 . 
     In some embodiments, the multi-flare mode conversion section may be a single-piece construction. The horn  504  in  FIG. 5 , for example, comprises a single-piece multi-flare mode conversion section  544 . The horn  504  may further comprise a sleeve  542  joined to the multi-flare mode conversion section  544 . The sleeve  542  may be configured to couple the horn  504  to a waveguide (e.g.,  212 ,  FIG. 2 ). 
       FIG. 6A  shows additional details of dielectric insert  206  in accordance with the present disclosure. In some embodiments, the dielectric insert  206  may be a tube, a rod, or other suitable elongate structure. The particular structure selected may be decided based on factors such as mechanical stability, thermal stability, expected operating environment, and so on. As noted above, the first portion  362  of dielectric insert  206  may be configured for being positioned and supported within the horn  204 . In some embodiments, the first portion  362  may include fingers  602  configured to secure the dielectric insert  206  to the horn  204 .  FIGS. 6B and 6C  show alternate configurations of the fingers  602 . Referring for a moment to  FIG. 7 , a magnified portion of the cross sectional view shown in  FIG. 3A  illustrates that dielectric insert  206  may be disposed within the throat of the horn  204 . The fingers  602  of the dielectric insert  206  can provide a friction fit with the interior surface of horn  204  for a self-supporting structure. The locking screws  304  may help to secure the dielectric insert  206  in position. In other embodiments, a web-like structure (not shown) may be used to support the dielectric insert  206 . 
     In some embodiments, the dielectric insert  206  may be a dielectric material comprising a quartz fiber weave construction supported by a cyanate-ester resin system that exhibits low-loss RF performance and suitable mechanical properties for the environment. In other embodiments, plastic materials such as Rexolite® plastic or Ultem® plastic may be used. In general, the dielectric insert  206  may comprise any material or combination of materials having suitable dielectric properties, mechanical properties, thermal properties and the like. 
       FIG. 6D  shows a cross-sectional view of an alternative embodiment of the dielectric insert  206 . In this embodiment, the dielectric insert  206  is a dielectric tube having an inner diameter  650  and an outer diameter  652 . As can be seen in the figure, in the illustrated embodiment both the diameters  650 ,  652  decrease with distance from the location  656  where the dielectric insert  206  contacts the interior surface of horn  204 . In other embodiments, only one of the diameters  650 ,  652  may decrease with distance from the location  626 . Decreasing the distance of one or both of the diameters  650 ,  652  may provide improved performance over a wide frequency range, such as the low frequency band and the high frequency band of a diplexer-polarizer unit (discussed below) of the feed assembly. In some embodiments, the thickness  654  of the dielectric tube may be constant with distance from the location  652 . In other embodiments, the thickness  654  may vary with distance from the location  652 . For example, the thickness  654  may decrease with distance from the location  652 , such as linearly decreasing with distance. Decreasing the thickness  654  may also provide improved performance over a wide frequency range, such as the low frequency band the high frequency band of the diplexer-polarizer unit (discussed below). 
     Operational characteristics of a feed (e.g.,  202 ,  FIG. 2 ) in accordance with the present disclosure will now be discussed. The term “dominant waveguide mode” refers to the propagation mode in a waveguide that propagates with minimum degradation (e.g., propagates with the lowest cutoff frequency). Furthermore, one of ordinary skill understands that the propagation modes in a waveguide may include:
         transverse electromagnetic (TEM) mode—This is a propagation mode in which neither the electric field nor the magnetic field are in the direction of propagation.   transverse electric (TE) mode: This is a propagation mode in which there is no electric field in the direction of propagation, but there is a non-zero magnetic field along the direction of propagation.   transverse magnetic (TM) mode: This is a propagation mode in which there is no magnetic field in the direction of propagation, but there is a non-zero electric field along the direction of propagation.   hybrid mode: This is a propagation mode in which there is a non-zero electric field and a non-zero magnetic field along the direction of propagation.       

     As explained with reference to  FIGS. 2-4 , the feed  202  comprises a horn  204  and a dielectric insert  206 . The multi-flare mode conversion section  344  of horn  204  may function in conjunction with the first portion  362  of dielectric insert  206  to convert a signal between a dominant waveguide mode and a hybrid mode. The hybrid mode may propagate along the second portion  364  of the dielectric insert  206  to define an illumination beam toward a reflector (e.g.,  112 ,  FIG. 1A ). 
     In some embodiments, the feed  202  may be used to transmit a transmit signal. Waveguide  212  can propagate the transmit signal in its dominant waveguide mode. The transmit signal may, for example, be provided to the waveguide  212  from a signal source (e.g., transceiver  20 ) via one or more suitable RF components such as those discussed above. The multi-flare conversion section  344  of the horn  204  may function in conjunction with the first portion  362  of the dielectric insert  206  to convert the transmit signal from the dominant waveguide mode to the hybrid mode. The hybrid mode may then propagate along the second portion  364  of the dielectric insert  206  and radiate largely from the distal end of the dielectric insert  206  to define the illumination beam directed toward the reflector. The reflector can then reflect the illumination beam to form a desired secondary beam in which the reflected electromagnetic energy adds constructively in a desired direction (e.g. the direction corresponding to the satellite), while partially or completely cancelling out in all other directions. 
     In other embodiments, the feed  202  may be used to receive a receive signal. The reflector can cause electromagnetic energy of the received signal to converge at the location of the feed  202  if an incident plane wave arrives from a desired direction (e.g., the direction corresponding to the satellite). The second portion  364  of the dielectric insert  206  can cause the converged electromagnetic energy to propagate along it in the hybrid mode. The multi-flare conversion section  344  of the horn  204  may function in conjunction with the first portion  362  of the dielectric insert  206  to convert the receive signal from the hybrid mode to the dominant waveguide mode. Waveguide  212  can then propagate the transmit signal in its dominant waveguide mode and provide the transmit signal to a receiver (e.g., transceiver  20 ) via one or more suitable RF components such as those discussed above. 
     In other embodiments, the feed  202  may be used to both transmit a transmit signal and receive a receive signal. The operation may, for example, be full duplex, may be time duplexed, or may be a combination of time duplexed with different and varying intervals of transmit and receive signal flow. 
     The radiation pattern from the hybrid mode has the often desirable properties of circular symmetry or pseudo circular symmetry in the main beam to a significant degree and corresponding low off axis cross-polarization energy. The hybrid mode radiation pattern is further defined as having high purity Huygens polarized source properties. In some embodiments, the dominant waveguide mode is a TE mode, which is typical in square waveguides and circular waveguides. 
     In accordance with the present disclosure, the hybrid mode produced by feed  202  may have minimal or at least reduced cross-polarization energy. Cross polarization refers to the polarization orthogonal to the polarization being discussed. For instance, if the fields from an antenna are meant to be horizontally polarized, the cross-polarization in this case would be vertical polarization. As another example, if the polarization is right hand circularly polarized, the cross-polarization would be left hand circularly polarized. The cross polarization energy may be expressed as a power level in units of dB, indicating how many decibels below the desired polarization&#39;s power level the cross polarization power level is, and is known as cross-polarization discrimination (XPD). In some embodiments, the XPD of the illumination beam may be less than −24.5 dB. 
     In some embodiments, the signal may comprise several frequencies (frequency components). The multi-flare mode conversion section  344  of horn  204  may function in conjunction with the first portion  362  of dielectric insert  206  to convert the signal between a dominant waveguide mode and a hybrid mode at each frequency. In some embodiments, the ratio between the frequency of the highest frequency component in the signal and the frequency of the lowest frequency component in the signal may be about 1.5 or higher. In some embodiments, the axial ratio of the illumination beam may be less than 1 dB at each of the frequencies when expressed as the ratio of the large quantity over the small quantity. 
     In accordance with the present disclosure, the dielectric insert  206  can improve the directivity of the illumination beam. In some embodiments, directivity may be computed as a ratio of the power of the signal measured along the axis of propagation to the total power in the signal. Propagation of the hybrid mode may be largely confined to the second portion  364  of the dielectric insert  206  to improve directivity. For example, in a configuration comprising only a horn and no dielectric insert, the illumination beam propagates along the horn and radiates from the aperture of the horn. The directivity of this illumination beam may be less than the directivity of an illumination beam that propagates along a dielectric insert (e.g.,  206 ) and radiates from the distal end of the dielectric insert. The improved directivity may be useful in a feed array (e.g.,  1000 ,  FIG. 10 ) because increased directivity can mitigate the challenge of having to isolate the individual horns in the feed array. 
     Increasing the length L of the second portion  364  of the dielectric insert  206  may increase feed directivity. However, the distribution of energy in the illumination beam decreases as the length L increases. Therefore, in a particular implementation, design decisions might be made to trade off energy distribution in the illumination beam for directivity of the secondary beam of the reflector. The reflector edge illumination values can be an indication of optimum illumination and the trade off between the portion of energy illuminating the reflector and the portion of energy spilling past the reflector (spillover energy). An edge illumination of approximately −8 to −14 dB relative to a central peak value can result in near optimum net efficiency and can be achieved with a feed assembly in accordance with the present disclosure. In some embodiments, the edge illumination may be less than −14 dB (e.g., −18 dB). In an example, a dual band full duplex feed may be designed for a near optimum illumination in a lower frequency band, and under illuminate the reflector in a higher frequency band. A single transmit or receive reflector with a SFPB horn design in either a focused or non-focused configuration with dense contiguous feeds in an array without the dielectric insert may have an edge illumination value of approximately −5 dB relative to a central peak value and will be substantially below the optimum illumination as a result of the spillover energy. The portion of cross-polarization energy detracts from the overall performance of the antenna system when frequency reuse and polarization are applied to provide isolated areas of coverage in the form of spot beams. Minimizing the cross-polarization is an often applied design objective in systems that use polarization for coverage signal isolation. 
     A feed assembly (e.g.,  114 ,  FIG. 2 ) in accordance with the present disclosure may be used with any suitable RF component.  FIG. 8 , for example, shows an illustrative embodiment of a feed assembly  814  in accordance with the present disclosure. The feed  802  may comprise a horn  804  and a dielectric insert  806 . The horn  804  may comprise a single-piece multi-flare mode conversion section  844  coupled to a sleeve  842 . The dielectric insert  806  may have a first portion (not shown) disposed within the horn  804 , and a second portion that extends beyond an aperture  842  of the horn  804 . 
     In some embodiments, the feed assembly  814  may further comprise a housing  824  which may house an RF component (not shown). In some embodiments, the RF component may be a diplexer-polarizer unit ( 826 ,  FIG. 8A ). It will be appreciated, of course, that in other embodiments, the feed  802  may be used with RF components other than a diplexer-polarizer. For example, in some embodiments, the feed  802  may be used in combination with RF components such as a four-port OMT, a two-port OMT, a single-band septum polarizer, a dual-band septum polarizer, a polarizer and a filter, and so on. 
     Referring to  FIG. 8A , the hidden line view of feed assembly  814  shown in the figure illustrates that a portion of the dielectric insert  806  may extend into the horn  804  and through the multi-flare mode conversion section  844  where the dielectric insert  806  can be supported at the throat of horn  804 . A portion of the dielectric insert  806  may extend beyond the aperture  842  of horn  804 . The figure shows the diplexer-polarizer unit  826  disposed within the housing  824 . 
       FIG. 9  shows an illustrative embodiment of diplexer-polarizer unit  826  depicted in  FIG. 8A . The diplexer-polarizer unit  826  may comprise a diplexer  902 , waveguides  904   a ,  904   b  coupled to the diplexer  902 , and a polarizer  906 . In some embodiments, the diplexer  902  may be a 4-port diplexer. The waveguides may be divided into high-side waveguides  904   a  to transmit and receive signals in a high frequency band and low-side waveguides  904   b  to transmit and receive signals in a low frequency band, as indicated by dividing plane  92 . Merely to provide an illustrative example of the use of a diplexer-polarizer for a dual-band full-duplex configuration, the high frequency band may span a range of about 27.5-31.0 GHz (a bandwidth of about 3.5 GHz) and the low frequency band may span a range of about 17.7-21.2 GHz (a bandwidth of about 3.5 GHz). 
     The waveguides  904   a ,  904   b  may be further divided according to the polarization of the signal propagated in the waveguides, as indicated by dividing plane  94 . For example, the high-side waveguides  904   a  may comprise one waveguide configured to transmit and receive right hand circularly polarized signals and another waveguide configured to transmit and receive left hand circularly polarized signals. Similarly, the low-side waveguides  904   b  may comprise one waveguide to transmit and receive right hand circularly polarized signals and another waveguide to transmit and receive left hand circularly polarized signals. 
       FIG. 9A  is a hidden line representation of the diplexer-polarizer unit  826 . In some embodiments, the polarizer  906  may comprise a square waveguide  962  having a staircase septum polarizer  964  disposed within the square waveguide  962 . The septum polarizer  964  may divide the waveguide  962  into a first waveguide portion  966   a  and a second waveguide portion  966   b , as indicated in the figure by the dividing plane  96 . The septum polarizer  964  may be configured to convert signals between a polarized state in the waveguide  962  and a first polarization component in the first waveguide portion  966   a  and a second polarization component in the second waveguide portion  966   b . In some embodiments, the first polarization component may correspond to a first polarization at the aperture  842  of horn  802  shown in  FIG. 8 . Similarly, the second polarization component may correspond to a second polarization at the aperture  842  of horn  802 . In some embodiments, the first polarization may be a first circular polarization and the second polarization may be a second circular polarization different from the first circular polarization. 
     The hidden line representation of  FIG. 9A  reveals that waveguides  904   a  comprise high-side ports  942   a ,  942   b  and waveguides  904   b  comprise low-side ports  944   a ,  944   b . In some embodiments, the ports  942   a  and  944   a  may be configured to transmit and receive right hand circularly polarized signals, and the ports  942   b ,  944   b  may be configured to transmit and received left hand circularly polarized signals. 
       FIG. 9B  shows a perspective view of an air model of an alternative embodiment of diplexer-polarization unit  826 .  FIG. 9C  is a top view of the diplexer-polarization unit  826  of  FIG. 9B . In the illustration of  FIG. 9B , the diplexer-polarization unit  826  is rotated 90-degrees along the axis of the polarizer  906  relative to the illustration in  FIGS. 9 and 9A . The septum polarizer  964  may divide the waveguide  962  into first waveguide portion  966   a  and second waveguide portion  966   b . As indicated by dividing plane  98 , the first waveguide portion  966   a  is associated with a first polarization and the second waveguide portion  966   b  is associated with a second polarization. In the illustrated example, the first polarization is left hand circularly polarized, and the second polarization is right hand circularly polarized. Alternatively, the polarizations may be different. 
     Diplexer  902  incudes a first pair of waveguides  932  coupled to the first waveguide portion  966   a . The first pair of waveguides  932  includes a high-side waveguide  932   a  and a low-side waveguide  932   b . The high-side waveguide  932   a  includes a filter configured to communicate signals in the high frequency band between the first waveguide portion  966   a  and high-side port  952   a . Similarly, the low-side waveguide  932   b  includes a filter configured to communicate signals in the low frequency band between the first waveguide portion  966   a  and low-side port  954   a . In the illustrated example, each of the filters of the high-side and low-side waveguides  932   a ,  932   b  include multiple E-plane elements that may be of varying stub lengths with varying lengths of interconnecting waveguides between the E-plane elements. In other embodiments, each filter may be different. In some embodiments, each filter may include at least one of an input matching section and an output matching section. 
     Diplexer  902  further includes a second pair of waveguides  934  coupled to the second waveguide portion  966   b . The second pair of waveguides  934  includes a high-side waveguide  934   a  and a low-side waveguide  934   b . The high-side waveguide  934   a  includes a filter configured to communicate signals in the high frequency band between the second waveguide portion  966   b  and high-side port  952   b . Similarly, the low-side waveguide  934   b  includes a filter configured to communicate signals in the low frequency band between the second waveguide portion  966   b  and low-side port  954   b . In the illustrated example, the filters of the high-side and low-side waveguides  934   a ,  934   b  are the same as those of the high-side and low-side waveguides  932   a ,  932   b  respectively. In other embodiments, the filters may be different. In some embodiments, each filter may include at least one of an input matching section and an output matching section. 
     In the illustrated embodiment of  FIGS. 9B and 9C , the  4  ports  952   a ,  952   b ,  954   a ,  954   a  of the diplexer  902  are arranged in a row along an E-plane of the pairs of waveguides  932 ,  934  in a direction normal to the dividing plane  98 . Having the ports arranged in a row can permit efficient transition to an edge-launch circuit board interface within a transceiver (e.g., ref. no.  20  of  FIG. 2 ) In the illustrated example, the low-side ports  954   a ,  954   b  are arranged between the high-side ports  952 ,  952   b . Accordingly, in this example the filter of low-side waveguide  932   b  has a first waveguide wall that is shared with the filter of high-side waveguide  932   a , and has a second waveguide wall that is shared with the filter of low-side waveguide  934   b . Similarly, the low-side waveguide  934   b  has a first (already mentioned) waveguide wall that is shared with the filter of the low-side waveguide  932   b , and a second waveguide wall that is shared with the filter of the high-side waveguide  934   a . As used herein, shared waveguide walls refers to conductive material (e.g., metal) having a first surface that forms the waveguide wall of a first filter of a first waveguide and having a second surface opposing the first surface that forms the waveguide wall of a second filter of a second waveguide, where the conductive material extends between the first surface and the second surface. The conductive material extending between the first surface and the second surface may for example be a solid material or a web of interconnected material. Having the filters share walls can provide one or more benefits including minimizing the amount of material needed to form the diplexer  902 , minimizing the mass of the diplexer  902 , and/or maximizing the volumetric efficiency of the diplexer. In other embodiments, the pairs of waveguides may be arranged differently (e.g., in a 2×2 arrangement as shown  FIGS. 9 and 9A ), and thus the filters that share walls can be different. 
     Referring to  FIG. 10 , in some embodiments, a feed array  1000  may comprise an array of feed assemblies  1002  in accordance with the present disclosure. Illustrative examples of feed assemblies  1002  are shown in  FIGS. 2 and 8 . In some embodiments, the spacing (e.g., center-to-center spacing, s) between the horns of adjacent feed assemblies  1002  may be the same. Merely to illustrate, for example, in some embodiments, the spacing s between the horns of adjacent feed assemblies  1002  may be about 2.5 wavelengths of a highest frequency of the signal to be transmitted or received. In other embodiments, the spacing s between horns of adjacent feed assemblies  1002  may vary. 
     The feed assemblies  1002  comprising the feed array  1000  may be arranged in a regular pattern. In some embodiments, for example, the feed assemblies  1002  may be arranged in a lattice. For example, feed assemblies  1002  shown in  FIG. 10  are arranged in a hexagonal lattice. In some embodiments, the feed assemblies  1002  may be arranged in a rectilinear pattern. In other embodiments, the feed assemblies  1002  may be arranged in a triangular pattern. In still other embodiments, the feed assemblies  1002  may be arranged in an irregular pattern. 
     In some embodiments, the feed assemblies  1002  comprising the feed array  1000  may be arranged in a planar configuration. For example, the feed assemblies  1002  may be disposed on a planar surface so that the distal ends of the dielectric inserts of the feed assemblies  1002  lie on a plane. In other embodiments, the feed assemblies  1002  comprising the feed array  1000  may be arranged in non-planar configurations. For example, in some embodiments, the feed array  1000  may be arranged on a convex surface or a concave surface relative to the curvature of the reflector (e.g.,  112 ,  FIG. 1A ). More generally, in other embodiments, the feed array  1000  may be arranged on a surface having any suitable contour. 
     The feed array  1000  may be incorporated in a reflector antenna of a satellite.  FIG. 11 , for example, shows a reflector antenna  1100  for a satellite (e.g., satellite  105 ,  FIG. 1 ) that incorporates feed array  1000 . The reflector antenna  1100  is an example of an offset fed parabolic reflector configuration. However, it will be appreciated that the feed array  1000  may be incorporated in other antenna configurations. 
     In the configuration shown in  FIG. 11 , the feed array  1000  lies within the focal plane of the reflector  1112 . In other embodiments, the feed array  1000  may lie on the focal plane, or beyond the focal plane of reflector  1112 . 
     Referring to  FIG. 12 , a process for designing a feed (e.g.,  202 ,  FIG. 2 ) in accordance with the present disclosure will be explained. In some embodiments, the process may be performed using suitable simulation tools. The feed may be designed using, for example, the High Frequency Structure Simulator (HFSS) software available from Ansys, Inc. Alternatively, other software may be used to design the feed. 
     At block  1202 , a suitable reflector (e.g.,  112 ,  FIG. 1A ) design may be selected. For example, the shape of the reflector may be specified, the dimensions of the reflector may be specified, and so on. 
     At block  1204 , a feed may be positioned relative to the reflector. This may include designing a horn (e.g.,  204 ,  FIG. 2 ) by selecting an initial number of flare angles and their initial values, and designing a dielectric insert (e.g.,  206 ,  FIG. 2 ) by selecting an initial length L ( FIG. 3A ) of the portion of the dielectric insert that extends beyond the aperture of the horn. 
     At block  1206 , an illumination beam directed toward the reflector may be simulated. A cross-polarization of the illumination beam may be computed. If at block  1208 , the cross-polarization is greater than a predetermined value, then processing may proceed to block  1210 . At block  1210 , one or more of the flare angles may be adjusted. Processing may return to block  1206 , where a cross-polarization is recomputed with the adjusted flare angle(s). The flare angles may be iteratively adjusted in this way until the cross-polarization of the illumination beam directed toward the reflector becomes less than or equal to the predetermined value (goal). At block  1208 , when the cross-polarization goal has been met, processing may continue to block  1212 . 
     At block  1212 , a directivity metric of the illumination beam that is directed toward the reflector may be computed. If at block  1214 , the directivity metric is not equal to a predetermined value, then processing may proceed to block  1216 . At block  1216 , the length L of the portion of the dielectric insert that extends beyond the aperture of the horn may be adjusted. In some embodiments, the length may be increased or decrease depending on whether the directivity computed at block  1212  is greater than or less than the predetermined value. Processing may return to block  1212 , where a directivity metric is recomputed with the adjusted length. The length L may be iteratively adjusted in this way until the directivity metric of the illumination beam directed toward the reflector reaches the predetermined value (goal), at which time the design process may complete. 
     Referring back to block  1204 , in some embodiments, a feed array (e.g.,  1000 ,  FIG. 10 ) may be positioned relative to the reflector. At block  1206 , the cross-polarization may be computed for an illumination beam of at least one of the feeds in the feed array directed towards the reflector. At block  1208 , the flare angles of each of the feeds comprising the feed array may be adjusted, and the process may be iterated until the cross-polarization of the illumination beam becomes less than or equal to a predetermined value. Similarly, in blocks  1212 - 1216 , the lengths of each dielectric insert in the feed array may be iteratively adjusted until the directivity metric of an illumination beam from at least one of the feeds in the feed array reaches a predetermined value. 
     Referring back to block  1206 , in some embodiments, cross-polarization may be computed for two or more angles of the illumination beam. At block  1208 , the cross-polarization goal may be that the cross-polarization for each angle of the illumination beam be less than or equal to a predetermined value. In some embodiments, each angle may have a corresponding predetermined value that the cross-polarization is compared to. 
     In other embodiments, at block  1206 , cross-polarization may be computed for two or more frequencies of the illumination beam. At block  1208 , the cross-polarization goal may be that the cross-polarization for each frequency be less than or equal to a predetermined value. In some embodiments, each frequency may have a corresponding predetermined value that the cross-polarization is compared to. 
     Referring to  FIG. 13 , an illustrative implementation of a design system to facilitate the design of a feed (e.g.,  202 ,  FIG. 2 ) may include a computer system  1302  having a processing unit  1312 , a system memory  1314 , and a system bus  1311 . The system bus  1311  may connect various system components including, but not limited to, the processing unit  1312 , the system memory  1314 , an internal data storage device  1316 , and a communication interface  1313 . In a configuration where the computer system  1302  is a mobile device (e.g., smartphone, computer tablet), the internal data storage  1316  may or may not be included. 
     The processing unit  1312  may comprise a single-processor configuration, or may be a multi-processor architecture. The system memory  1314  may include read-only memory (ROM) and random access memory (RAM). The internal data storage device  1316  may be an internal hard disk drive (HDD), a magnetic floppy disk drive (FDD, e.g., to read from or write to a removable diskette), an optical disk drive (e.g., for reading a CD-ROM disk, or to read from or write to other high capacity optical media such as the DVD, and so on). In a configuration where the computer system  1302  is a mobile device, the internal data storage  1316  may be a flash drive. 
     The internal data storage device  1316  and its associated non-transitory computer-readable storage media provide nonvolatile storage of data, data structures, computer-executable instructions, and so forth. Although the description of computer-readable media above refers to a HDD, a removable magnetic diskette, and a removable optical media such as a CD or DVD, it is noted that other types of media which are readable by a computer, such as zip drives, magnetic cassettes, flash memory cards, cartridges, and the like, may also be used, and further, that any such media may contain computer-executable instructions for performing the methods disclosed herein. 
     The system memory  1314  and/or the internal data storage device  1316  may store a number of program modules, including an operating system  1332 , one or more application programs  1334 , program data  1336 , and other program/system modules  1338 . For example, the application programs  1334 , which when executed, may cause the computer system  1302  to perform method steps of  FIG. 12 . The application programs  1334  may also include simulation software (e.g., the HF SS software mentioned above). An external data storage device  1342  may be connected to the computer system  1302 , for example, to store the design data for a feed or feed array. 
     Access to the computer system  1302  may be provided by a suitable input device  1344  (e.g., keyboard, mouse, touch pad, etc.) and a suitable output device  1346 , (e.g., display screen). In a configuration where the computer system  1302  is a mobile device, input and output may be provided by a touch sensitive display. 
     The computer system  1302  may operate in a networked environment using logical connections via wired and/or wireless communications to one or more remote computers (not shown) over a communication network  1352 . The communication network  1352  may be a local area network (LAN) and/or larger networks, such as a wide area network (WAN). 
     Embodiments described herein can provide a very light weight solution for enhanced aperture directivity to achieve a near optimum efficiency that improves off-axis cross-polarization that is applicable to high through-put satellite antenna architectures. The light weight attribute can be increasingly important for arrays of feeds of large numbers. The shaped horn affords optimizing gain, cross-polarization and impedance match in a feed array environment or for isolated feeds. 
     The above description illustrates various embodiments of the present disclosure along with examples of how aspects of the particular embodiments may be implemented. The above examples should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the particular embodiments as defined by the following claims. Based on the above disclosure and the following claims, other arrangements, embodiments, implementations and equivalents may be employed without departing from the scope of the present disclosure as defined by the claims.