Abstract:
A waveguide has distal, medial and proximal sections. The distal and medial sections rotate relative to each other and to the proximal section. In a first configuration, the waveguide transforms linearly polarized electromagnetic radiation at the proximal end of the proximal section to linearly polarized electromagnetic radiation at the distal end of the distal section and vice versa. In a second configuration, the waveguide transforms linearly polarized radiation at the proximal end of the proximal section into circularly polarized electromagnetic radiation at the distal end of the distal section and vice versa. Preferably, the distal and medial sections include respective eight-wavelength polarizers and the proximal section includes a quarter-wavelength polarizer. A multi-band antenna feed includes two such waveguides, one nested inside the other, for transforming electromagnetic radiation of respective frequency bands.

Description:
This application claims priority of U.S. Provisional Patent Application No. 61/428,248, filed Dec. 30, 2010 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to electromagnetic communication between the ground and an orbiting satellite and, more particularly, to a feed assembly, for a ground station antenna, that supports communication with satellites that transmit and receive in several frequency bands and/or using linear and circular polarizations. 
       FIGS. 1A and 1B  shows a typical parabolic dish antenna  10  for communicating with a communication satellite such as a Fixed Service Satellite (FSS). Antenna  10  includes a parabolic dish  12  and a Low Noise Block downconverter Feed horn (LNBF)  14  supported by supports  16  at the focus of dish  12 . Dish  12  is mounted on a mount  18 .  FIG. 1A  is a perspective view of antenna  10 .  FIG. 1B  is a frontal view of dish  12  and LNBF  14 . LNBF  14  includes a Low Noise Block (LNB) with two orthogonal receive dipoles  20  shown in  FIG. 1B  in phantom. Each dipole receives Ku-band signals from the FSS at which antenna  10  is aimed. 
     An FSS is a geostationary satellite whose transponders transmit and receive linearly polarized radio waves in the Ku-band. One transponder of a transponder pair transmits and receives horizontally polarized waves. The other transponder of the transponder pair transmits and receives vertically polarized waves. LNB dipoles  20  are intended for receiving signals in respective allocated frequency segments from respective transceivers of the FSS: the horizontal dipole antenna  20  is for receiving signals from the transponder that transmits horizontally polarized waves and the vertical dipole antenna  20  is for receiving signals from the transponder that transmits vertically polarized waves. If the FSS is at the same longitude as a stationary antenna  10 , then when dish  12  is aimed at the FSS by appropriate adjustment of mount  18  in azimuth and elevation, the horizontal LNB dipole  20  is aligned with the horizontal polarization direction of the FSS and the vertical LNB dipole  20  is aligned with the vertical polarization of the FSS. If the FSS is not at the same longitude as a stationary antenna  10  then the polarization directions of the FSS are tilted with respect to LNB dipoles  20  and dish  12  must be rotated, as indicated by an arrow  22  in  FIG. 1B , to align LNB dipoles  20  with the polarization directions of the FSS. 
     If antenna  10  is stationary, then dish  12  only needs to be rotated once and then fixed in place on mount  18 . If antenna  10  is mounted on a moving platform such as a truck, a boat, an aircraft or some other vehicle, the orientation of dish  12  must be adjusted continuously to keep dish  12  pointed at the FSS and to keep LNB dipoles  20  aligned with the polarization directions of the FSS. Even if antenna  10  is stationary, if antenna  10  communicates with a satellite that is not in a geosynchronous obit, dish  12  must be adjusted continuously to keep dish  12  pointed at the satellite and to keep LNB dipoles  20  aligned with the satellite&#39;s polarization directions. Hsiung, in U.S. Pat. No. 6,377,211, teaches an antenna aiming apparatus for keeping an antenna that is mounted on a moving vehicle properly aligned with a satellite in a non-geosynchronous orbit. U.S. Pat. No. 6,377,211 is incorporated by reference for all purposes as if fully set forth herein. 
     U.S. patent application Ser. No. 12/555,007, which is incorporated by reference for all purposes as if fully set forth herein, teaches a LNBF that makes it unnecessary to rotate dish  12  as a whole, in the directions indicated by arrow  22 , to keep LNB dipoles  20  aligned with the polarization directions of the satellite with which antenna  10  communicates. 
       FIGS. 2A-2D  illustrate two embodiments  30  and  31  of a LNBF of U.S. Ser. No. 12/555,007.  FIG. 2A  is a side view of LNBF  30  showing that LNBF  30  includes, in series, a feed horn  48 , a waveguide  50  and a LNB  35 .  FIG. 2B  is a side view of LNBF  31  showing that LNBF  31  includes, in series, feed horn  48 , waveguide  50  and an Orthogonal Mode Transducer (OMT)  36 . Waveguide  50  includes a rotating distal section  32  and a fixed proximal section  34 .  FIG. 2C , a cross section of LNBF  30  through section A-A, shows that rotating distal section  32  of LNBF  30  includes a quarter-wavelength dielectric slab polarizer  42 .  FIG. 2D , a cross section of LNBF  30  through section B-B, shows that fixed proximal section  34  of LNBF  30  includes a quarter-wavelength dielectric slab polarizer  44 . Also shown in phantom in  FIG. 2D  are the orientations of the horizontal dipole  38  and the vertical dipole  40  of LNB  35 . Slab  44  is fixed at a 45-degree angle to both horizontal dipole  38  and vertical dipole  40 . OMT  36  includes, instead of two orthogonal dipoles, a horizontal port  39  that corresponds to dipole  38  and a vertical port  41  that corresponds to dipole  39 . 
     In general, a single quarter-wavelength dielectric slab polarizer that is placed at a 45-degree angle to a linearly polarized electromagnetic wave, transverse to the direction of propagation of the linearly polarized electromagnetic wave, transforms the linearly polarized electromagnetic wave to a circularly polarized electromagnetic wave. Appropriate rotation of just rotating distal section  32 , as indicated by an arrow  46  in  FIG. 2C , suffices to keep LNB dipoles  38  and  40  aligned with the polarization directions of the satellite with which an antenna that includes LNBF  30  communicates. Specifically, distal section  32  is rotated to place slab  42  at a 45-degree angle to the polarization directions of the satellite. Distal section  32  transforms the linearly polarized signal from the satellite to a circularly polarized signal, and fixed proximal section  34  transforms the circularly polarized signal to a linearly polarized signal that is aligned correctly with the appropriate LNB dipole  38  or  40 . Mathematical details are provided in U.S. Ser. No. 12/555,007. 
     To minimize reflections in waveguide  50 , slabs  42  and  44  should be tapered in the direction of propagation, as shown in  FIG. 3 . The lengths A and B should satisfy 2A+B≈0.25λ/√∈, where λ is the wavelength of the electromagnetic signal in free space and ∈ is the dielectric constant of the dielectric material of slabs  42  and  44 . Length C is tuned for optimal matching of the propagating wave through waveguide  50 . Typical values of A, B and C for a Ku-band LNBF  30  are 2 mm, 4 mm and 4 mm, respectively. The dielectric material of slabs  42  and  44  should be of low loss tangent at the operating frequency, e.g. Plexiglas™ (polymethyl methacrylate). 
       FIG. 4 , which is adapted from FIG. 2 of U.S. Pat. No. 6,377,211, is a simplified block diagram of a mechanism for pointing a parabolic dish antenna, that includes LNBF  31  and that is mounted on a moving vehicle, at a geostationary earth satellite while rotating distal section  32  to keep OMT ports  39  and  41  aligned with the polarization directions of the satellite. A Global Positioning System (GPS) receiver  110  mounted on the vehicle receives signals from GPS satellites in a known manner and produces signals that represent vehicle position, the current time (coordinated Universal Time or UPC) and a one-pulse-per-second timing pulse, all of which are applied to a Digital Signal Processor (DSP)  112 . The vehicle position information includes latitude, longitude and altitude. A vehicle speed sensor  114  produces signals representing the speed of the vehicle, which are applied to DSP  112 . DSP  112  also receives signals representing vehicles roll, inclination (pitch) and azimuth angle (yaw) from (an) appropriate sensor(s)  116  mounted on the vehicle. One such sensor is the Crossbow Model HDX-AHRS, available from Crossbow Technology, Inc. of San Jose Calif., that senses roll, inclination and azimuth angle, and that includes a three-axis magnetometer to make a true measurement of magnetic heading. The azimuth information may be in the form of signals representing vehicle yaw relative to magnetic north; magnetic correction then can be performed in DSP  112  based on the location information from GPS receiver  110  together with stored magnetic declination data. GPS receiver  110 , orientation sensor(s)  116  and speed sensor  114  provide DSP  112  with data at an update rate faster than once per second, thereby allowing the antenna pointing system to have a near-real-time response. 
     The location of the satellite also is stored in DSP  112 . DSP  112  processes the sensor signals relative to the location of the satellite to produce antenna drive or control signals, which are applied to the drive motors of the parabolic dish antenna, including a motor for rotating distal section  32 , to keep LNBF  31  pointed at the satellite and to rotate distal section  32  to keep OMT ports  39  and  41  aligned with the polarization directions of the satellite. 
     It also is known to concentrically nest two or more waveguides, of a LNBF, that are tuned to two or more respective frequency bands, so that the ground station antenna can communicate with a satellite that transmits and receives in more than one frequency band without having to swap an LNBF of one band for an LNBF of another band. See, for example, West, U.S. Pat. No. 7,102,581, which is incorporated by reference for all purposes as if fully set forth herein. 
     It is shown in U.S. Ser. No. 12/555,007 that LNBF  30  can be used for communicating with a satellite that transmits and receives circularly polarized radio waves if slab  42  is kept at a 90 degree angle to slab  44 . This is not the case with LNBF  31 . It would be highly advantageous to have a LNBF, in which the proximal end of the waveguide is coupled to an OMT, and that can be used for communicating both with satellites that transmit and receive linearly polarized radio waves and with satellites that transmit and receive circularly polarized radio waves. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a waveguide including: (a) a distal section; (b) a medial section; and (c) a proximal section; wherein the distal section and the medial section are configured to rotate relative to each other and to relative to the proximal section; wherein, when the distal section and the medial section are in a first configuration relative to each other and to the proximal section, the waveguide transforms linearly polarized electromagnetic radiation input to a proximal end of the proximal section into linearly polarized electromagnetic radiation output from a distal end of the distal section and transforms linearly polarized electromagnetic radiation input to the distal end of the distal section into linearly polarized electromagnetic radiation output from the proximal end of the proximal section; wherein, when the distal section and the medial section are in a second configuration relative to each other and to the proximal section, the waveguide transforms linearly polarized electromagnetic radiation input to the proximal end of the proximal section into circularly polarized electromagnetic radiation output from the distal end of the distal section and transforms circularly polarized electromagnetic radiation input to the distal end of the distal section into linearly polarized electromagnetic radiation output from the proximal end of the proximal section; and wherein the distal section and the medial section are rotated differently with respect to each other in the second configuration than in the first configuration. 
     According to the present invention there is provided a back end, for an orthogonal mode transducer that includes a port for exchanging signals of a certain polarization, the back end including: (a) a diplexer, for being coupled operationally to the port; (b) a block up-converter; (c) a low noise block; (d) a receive reject filter wherethrough the block up-converter is operationally coupled to the diplexer; and (e) a transmit reject filter, wherethrough the low noise block is opearationally coupled to the diplexer. 
     A basic waveguide of the present invention includes three sections: a distal section, a medial section and a proximal section. The distal and medial sections are configured to rotate relative to each other and relative to the proximal section. When the distal and medial sections are in a first configuration relative to each other and to the proximal section, the waveguide transforms linearly polarized radiation that is input to the proximal end of the proximal section into linearly polarized electromagnetic radiation (usually but not necessarily polarized in a different direction) that is output from the distal end of the distal section (for example, for transmission to a satellite) and transforms linearly polarized electromagnetic radiation that is input to the distal end of the distal section into linearly polarized electromagnetic radiation (usually but not necessarily polarized in a different direction) that is output from the proximal end of the proximal section (for example for receiving transmissions from a satellite). When the distal and medial sections are in a second configuration relative to each other and to the proximal section, the waveguide transforms linearly polarized radiation that is input to the proximal end of the proximal section into circularly polarized electromagnetic radiation that is output from the distal end of the distal section (for example, for transmission to a satellite) and transforms circularly polarized electromagnetic radiation that is input to the distal end of the distal section into linearly polarized electromagnetic radiation that is output from the proximal end of the proximal section (for example for receiving transmissions from a satellite). The distal section and the medial section are rotated differently with respect to each other in the second configuration than in the first configuration. 
     Preferably, the distal and medial sections include respective eight-wavelength polarizers and the proximal section includes a quarter-wavelength polarizer. In some embodiments, the polarizers include respective dielectric slabs. In other embodiments, the polarizers are quad ridge polarizers. 
     Preferably, the angular orientation of the distal section to the medial section in the second configuration is displaced by 90 degrees from the angular orientation of the distal section to the medial section in the first configuration. 
     The scope of the present invention also includes an antenna feed that includes the waveguide of the present invention. Preferably, the antenna feed also includes an orthogonal mode transducer that is operationally coupled to the proximal end of the proximal section of the waveguide. Most preferably, the orthogonal mode transducer is fixedly attached to the proximal end of the proximal section of the waveguide. 
     Also most preferably, the orthogonal mode transducer includes a first port for exchanging vertically polarized signals and a second port for exchanging horizontally polarized signals. Each port has a diplexer operationally coupled thereto. A block up-converter is operationally coupled to the diplexer via a receive reject filter. A low noise block is operationally coupled to the diplexer via a transmit reject filter. 
     The scope of the present invention also includes a ground station antenna that includes the antenna feed of the present invention and a mechanism for rotating the distal and medial sections of the waveguide relative to each other and relative to the proximal section of the waveguide to place the waveguide alternately and reversibly in either of its two configurations. 
     The scope of the present invention also includes a multi-band antenna feed that includes two waveguides of the present invention, each waveguide for transforming electromagnetic radiation of respective frequency bands. One waveguide is nested within the other waveguide. The waveguides could have circular cross sections, in which case the inner waveguide is nested concentrically within the outer waveguide. Alternatively, the waveguides could have rectangular cross sections. 
     Preferably, the multi-band antenna feed also includes, for each waveguide, a respective orthogonal mode transducer operationally coupled to the proximal end of the proximal section of the waveguide. Each orthogonal mode transducer includes a first port for exchanging vertically polarized signals and a second port for exchanging horizontally polarized signals. Each port has a diplexer operationally coupled thereto. A block up-converter is operationally coupled to the diplexer via a receive reject filter. A low noise block is operationally coupled to the diplexer via a transmit reject filter. 
     The respective frequency bands of the waveguides could be the C and X-bands, the C and Ku-bands, the C and Ka-bands, the X and Ku-bands, the X and Ka-bands, or the Ku and Ka-bands. 
     The scope of the present invention also includes, as an invention in its own right, the kind of back end that is coupled to the orthogonal mode transducer(s) of the antenna feed(s) of the present invention: a diplexer for being coupled operationally to a port of the orthogonal mode transducer, a block up-converter coupled operationally to the diplexer via a receive reject filter, and a low noise block operationally coupled to the diplexer via a transmit reject filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIGS. 1A and 1B  show a prior art parabolic dish antenna; 
         FIGS. 2A-2D  illustrate a prior art LNBF for keeping a moving ground station antenna aligned with a satellite that transmits and received linearly polarized electromagnetic waves; 
         FIG. 3  illustrates the tapering of the dielectric slab polarizers of the LNBF of  FIGS. 2A-2D ; 
         FIG. 4  is a simplified block diagram of a prior art mechanism for pointing a moving ground station antenna at a geostationary satellite; 
         FIGS. 5A-5E  illustrate a LNBF of the present invention; 
         FIG. 6  illustrates the tapered eighth-wavelength dielectric slab polarizers of the LNBF of  FIGS. 5A-5E ; 
         FIGS. 7A-7C  show dual-band antenna feeds of the present invention, each with its two nested waveguides configured for communicating with a satellite that transmits and receives linearly polarized electromagnetic radiation; 
         FIG. 8A-8C  show dual-band antenna feeds of the present invention, each with its two nested waveguides configured for communicating with a satellite that transmits and receives circularly polarized electromagnetic radiation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The principles and operation of a feed assembly for a ground station antenna according to the present invention may be better understood with reference to the drawings and the accompanying description. 
     The present invention is based on the insight that a straightforward modification of LNBF  31  renders LNBF  31  suitable for communicating either with a satellite that transmits and receives linearly polarized electromagnetic radiation or with a satellite that transmits and receives circularly polarized electromagnetic radiation. Referring again to the drawings,  FIGS. 5A-5E  and  6  illustrate such a modified LNBF  131 . LNBF  131  is LNBF  31  with distal section  32  of waveguide  50  split into two rotating sections of a waveguide  150 : a rotating distal section  132  and a rotating medial section  134 . Dielectric slab  42  is split transversely in half, into two dielectric slabs  142  and  144 , as shown in  FIG. 6 . As shown in  FIGS. 5B and 5C , to communicate with a satellite that transmits and receives linearly polarized electromagnetic radiation, distal section  132  and medial section  134  are rotated together, in the same manner as distal section  32 , with dielectric slabs  142  and  144  held parallel, so that dielectric slabs  142  and  144  function identically to dielectric slab  43 .  FIGS. 5B and 5C  are cross sections of LNBF  131  through sections A-A and B-B that correspond to  FIG. 2C . As shown in  FIGS. 5D and 5E , that also are cross-sections of LNBF  131  through sections A-A and B-B, to communicate with a satellite that transmits and receives circularly polarized electromagnetic radiation, distal section  132  is rotated so that dielectric slab  142  is oriented 45 degrees counter-clockwise relative to dielectric slab  44  and medial section  134  is rotated so that dielectric slab  144  is oriented 45 degrees clockwise relative to dielectric slab  44 . In  FIGS. 5D and 5E , dielectric slab  44  is shown in phantom behind dielectric slabs  142  and  144 . It can be shown that if dielectric slab  142  is held at the 45 degree counter-clockwise orientation relative to dielectric slab  44  that is shown in  FIG. 5D  and dielectric slab  144  is held at the 45 degree clockwise orientation relative to dielectric slab  44  that is shown in  FIG. 5E , then circularly polarized transmissions from a satellite that are received at feed horn  48  are transformed to linearly polarized received signals at OMT  36  and linearly polarized transmitted signals at OMT  36  are transformed into circularly polarized transmissions to the satellite at feed horn  48 . The ground station antenna in which LNBF  131  is mounted is provided with two motors for rotating distal section  132  and medial section  134 , in place of the single prior art motor for rotating distal section  32 . For communicating from a moving platform with a satellite that transmits and receives linearly polarized electromagnetic radiation, the motors rotate distal section  132  and medial section  134  together the way the prior art motor rotates distal section  32 . For communicating with a satellite that transmits and receives circularly polarized electromagnetic radiation, one motor rotates distal section  132  to the orientation shown in  FIG. 5D  and holds distal section  132  in that orientation, and the other motor rotates medial section  134  to the orientation shown in  FIG. 5E  and then holds medial section  134  in that orientation. 
     Just as prior art waveguides can be nested concentrically to enable a ground station antenna to communicate with a satellite that transmits and receives in more than one frequency band, so waveguides of the present invention can be nested concentrically to enable a ground station antenna to communicate with a satellite that transmits and receives in more than one frequency band.  FIGS. 7A and 8A  show a dual-band antenna feed, of the present invention, that includes two concentrically nested waveguides of the present invention, each with its respective OMT and back end. The inner waveguide is for communicating in the Ka-band (17.7 GHz to 31 GHz). The outer waveguide is for communicating in the Ku-band (10.7 GHz to 14.5 GHz).  FIG. 7A  shows the two waveguides configured for communicating with a satellite that transmits and receives linearly polarized electromagnetic radiation: distal sections  132  and medial sections  134  of the waveguides rotate together to function as quarter-wavelength polarizers.  FIG. 8A  shows the two waveguides configured for communicating with a satellite that transmits and receives circularly polarized electromagnetic radiation: distal sections  132  and medial sections  134  of the waveguides are fixed in place as separate eighth-wavelength polarizers. 
     Insets in  FIGS. 7A and 8A  also show that the propagation mode in the waveguides is the TE 11  mode. 
     Each OMT in  FIG. 7A  is coupled to its own back end for receiving vertically and horizontally polarized signals to transmit from respective Block Up-Converters (BUCs) and for sending received vertically and horizontally polarized signals to respective LNBs. The vertical polarization port  152  of the Ku-band OMT is coupled, via a diplexer  154  and a receive reject filter  156 , to the Ku-band vertical polarization BUC  160 , and, via diplexer  154  and a transmit reject filter  158 , to the Ku-band vertical polarization LNB  162 . The horizontal polarization port  164  of the Ku-band. OMT is coupled, via a diplexer  166  and a receive reject filter  168 , to the Ku-band horizontal polarization BUC  172 , and, via diplexer  166  and a transmit reject filter  170 , to the Ku-band horizontal polarization LNB  174 . Similarly, the vertical polarization port  176  of the Ka-band OMT is coupled, via a diplexer  178  and a receive reject filter  180 , to the Ka-band vertical polarization BUC  184 , and, via diplexer  178  and a transmit reject filter  182 , to the Ka-band vertical polarization LNB  186 ; and the horizontal polarization port  188  of the Ka-band OMT is coupled, via a diplexer  190  and a receive reject filter  192 , to the Ka-band horizontal polarization BUC  196 , and, via diplexer  190  and a transmit reject filter  194 , to the Ka-band horizontal polarization LNB  198 . To achieve the required Cross Polarization Discrimination (XPD) of better than 30 dB in transmission and better than 25 dB in reception, the diplexers and the filters need to be load-matched in their respective bands. These back ends support simultaneous transmission and reception in both polarizations in both frequency bands. 
     The following table shows the XPD of the configuration of  FIG. 7A . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Rx frequency 
                 Tx frequency 
                 XPD in 
                 XPD in 
               
               
                   
                 (GHz) 
                 (GHz) 
                 Rx 
                 Tx 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ku-band 
                 10.7-12.75 
                 13.75-14.5 
                 &gt;25 
                 &gt;30 
               
               
                 Ka-band 
                 17.7-21.2  
                 27.5-31  
                 &gt;20 
                 &gt;25 
               
               
                   
               
             
          
         
       
     
     The following table shows the XPD of the configuration of  FIG. 8A . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Rx frequency 
                 Tx frequency 
                 XPD in 
                 XPD in 
               
               
                   
                 (GHz) 
                 (GHz) 
                 Rx 
                 Tx 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ku-band 
                 10.7-12.75 
                 13.75-14.5 
                 &gt;22 
                 &gt;27 
               
               
                 Ka-band 
                 17.7-21.2  
                 27.5-31  
                 &gt;17 
                 &gt;22 
               
               
                   
               
             
          
         
       
     
     Waveguides of the present invention that are tuned to other frequency bands can be nested similarly and can be provided with similar, load-matched back ends. The following table shows the XPD of a nested waveguide configuration for linear polarization that is similar to the configuration of  FIG. 7A  but in which the inner waveguide is for the Ka-band and the outer waveguide is for the X-band (7.25 GHz to 8.4 GHz). This nested waveguide configuration is illustrated in  FIG. 7B . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Rx frequency 
                 Tx frequency 
                 XPD in 
                 XPD in 
               
               
                   
                 (GHz) 
                 (GHz) 
                 Rx 
                 Tx 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ka-band 
                 17.7-21.2 
                 27.5-31 
                 &gt;20 
                 &gt;25 
               
               
                 X-band 
                 7.25-7.75 
                     7.9-8.4 
                 &gt;25 
                 &gt;30 
               
               
                   
               
             
          
         
       
     
     The following table shows the XPD of a nested waveguide configuration for circular polarization that is similar to the configuration of  FIG. 8A  but in which the inner waveguide is for the Ka-band and the outer waveguide is for the X-band. This nested waveguide configuration is illustrated in  FIG. 8B . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Rx frequency 
                 Tx frequency 
                 XPD in 
                 XPD in 
               
               
                   
                 (GHz) 
                 (GHz) 
                 Rx 
                 Tx 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ka-band 
                 17.7-21.2 
                 27.5-31 
                 &gt;17 
                 &gt;22 
               
               
                 X-band 
                 7.25-7.75 
                     7.9-8.4 
                 &gt;22 
                 &gt;27 
               
               
                   
               
             
          
         
       
     
     The following table shows the XPD of a nested waveguide configuration for linear polarization that is similar to the configuration of  FIG. 7A  but in which the inner waveguide is for the Ku-band and the outer waveguide is for the C-band (3.4 GHz to 6.725 GHz). This nested waveguide configuration is illustrated in  FIG. 7C . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Rx frequency 
                 Tx frequency 
                 XPD in 
                 XPD in 
               
               
                   
                 (GHz) 
                 (GHz) 
                 Rx 
                 Tx 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ku-band 
                 10.7-12.75 
                 13.75-14.5 
                 &gt;25 
                 &gt;30 
               
               
                 C-band 
                 3.625-4.2   
                  5.85-6.425 
                 &gt;20 
                 &gt;25 
               
               
                   
               
             
          
         
       
     
     The following table shows the XPD of a nested waveguide configuration for circular polarization that is similar to the configuration of  FIG. 8  but in which the inner waveguide is for the Ku-band and the outer waveguide is for the C-band. This nested waveguide configuration is illustrated in  FIG. 8C . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Rx frequency 
                 Tx frequency 
                 XPD in 
                 XPD in 
               
               
                   
                 (GHz) 
                 (GHz) 
                 Rx 
                 Tx 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ku-band 
                 10.7-12.75 
                 13.75-14.5 
                 &gt;22 
                 &gt;27 
               
               
                 C-band 
                 3.625-4.2   
                  5.85-6.425 
                 &gt;17 
                 &gt;22 
               
               
                   
               
             
          
         
       
     
     The present invention is not limited to only two nested waveguides. The following table shows the preferred cross-sectional dimensions of two configurations of four nested waveguides for simultaneous transmission and reception in all four of the bands that are used for satellite communication. One configuration uses nested concentric waveguides of circular cross-section. The other configuration uses nested waveguides of rectangular cross-section. The innermost waveguide is the Ka-band waveguide that is nested inside a Ku-band waveguide. The Ku-band waveguide is nested inside an X-band waveguide. The X-band waveguide is nested inside a C-band waveguide. 
     
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Circular cross-section 
                 Rectangular cross section 
               
             
          
           
               
                 Frequency 
                 Inner diameter 
                 Outer diameter 
                 Height 
                 Width 
               
               
                 band 
                 (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
               
               
                   
               
             
          
           
               
                 Ka 
                   
                 12.79 
                 4.32 
                 10.67 
               
               
                 Ku 
                 12.79 
                 26.15 
                 9.53 
                 19.05 
               
               
                 X 
                 26.15 
                 45.62 
                 12.62 
                 28.50 
               
               
                 C 
                 45.62 
                 80.65 
                 29.08 
                 58.17 
               
               
                   
               
             
          
         
       
     
     The Ku-band XPDs configurations of  FIGS. 7 and 8  are adequate for separate transmission and reception but not for simultaneous transmission and reception. U.S. Ser. No. 12/555,007 points out that the dual quad ridge polarizer of Vezmar, U.S. Pat. No. 6,097,264, gives better XPD than the dielectric slab design described above. Using dual quad ridge polarizers in the distal  132 , medial  134  and proximal  34  sections of a Ka waveguide  150  gives XPDs of &gt;35 dB in transmission and &gt;20 dB in reception. 
     While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. Therefore, the claimed invention as recited in the claims that follow is not limited to the embodiments described herein.