Patent Publication Number: US-10320080-B2

Title: Tri-band feed assembly systems and methods

Description:
BACKGROUND 
     As is known in the art, conventional SATCOM terminals utilize small or low profile reflector antennas in applications having significant size constraints. The small or low profile reflector antennas typically include a feed assembly that transmits signals from a transmitter or receives signals to a receiver in the respective antenna system. However, the size of the feed assembly can limit the type of SATCOM applications the small or low profile reflector antennas can be utilized in. Further, many feed assemblies are only configured to provide and support single-band or dual-band operation. 
     SUMMARY 
     The concepts, systems and techniques disclosed herein provide a compact tri-band feed assembly for that operates at first, second and third frequency bands (e.g., low, mid and high frequency bands) and can be utilized in various reflector antenna applications. The tri-band feed assembly includes various components to provide a feed assembly having smaller dimensions as compared with feed assemblies known in the art. For example, in some embodiments, the feed assembly includes a compact feed horn and a compact match section that support low, mid and high frequency bands, a coaxial polarizer and an orthomode transducer (OMT) to support signals in a low frequency band, a polyrod and polarizer in a center conductor using circular waveguide to support signals in mid and high frequency bands, and a diplexer to separate one or more mid-band ports to a high-band port. Thus, the feed assembly provides a tri-band feed assembly having different portions to support signals in the low frequency band and signals in the mid and high frequency bands. 
     The tri-band feed assembly can be designed for relatively small or low profile reflector antennas for applications, such as, but not limited to, airborne, shipboard, or ground mobile platforms, having limited space for the respective reflector antennas. The components of the tri-band feed assembly can have smaller (e.g., compact) dimensions as compared to comparable components of other feed assemblies known in the art. For example, a length of the coaxial polarizer can be approximately equal to one-half a wavelength at a frequency of operation in the low frequency band. In embodiment, the coaxial polarizer includes one or more portions having a notched rectangular shape. In some embodiments, the reduced size can be achieved based at least in part on the properties of the one or more portions having a notched rectangular shape and the properties of the material used to form the coaxial polarizer. 
     The OMT can have compact dimensions such that two low band ports are disposed in close proximity but orthogonal to each other. In the coaxial waveguide, a pair of shorting fins are used to provide additional isolation between the two orthogonal ports. The distance between the two ports can be adjusted based on a return loss threshold and an isolation threshold of a respective reflector antenna. 
     Two key challenges of multi-band feed design for reflector antenna are having similar beamwidths and having a common phase center for all bands. With different beamwidths, antenna illumination or spillover efficiency will be compromised. Without having a common phase center, antenna phase efficiency will be compromised. The physics for a feed horn is that it usually has broader beamwidth at lower frequency and it becomes narrower as frequency increases. Most of the feed horns also have phase center locations vary with frequency. In embodiments, the respective beamwidths of the feed assembly at each of the low, mid and high frequency bands are approximately equal. For example, in some embodiments, the beamwidths (e.g., 10-db beam widths) for each of the low, mid and high frequency bands can be about 74 degrees. In embodiment, the feed assembly has a common phase center for each of the low, mid and high frequency bands to provide high antenna efficiencies at each of the low, mid and high frequency bands. 
     In a first aspect, a feed assembly for a reflector antenna is provided having a feed horn common to low, mid and high frequency bands, a coaxial polarizer to launch signals in the low band frequency band and supports the mid and high frequency bands, a coaxial orthomode transducer (OMT) to launch signals in the low band frequency band and supports the mid and high frequency bands, and a polyrod disposed in a center conductor of the feed assembly, the polyrod common to the mid and high frequency bands and supports the low frequency band. 
     A length of the coaxial polarizer may correspond to one-half a wavelength at an operating frequency in the low frequency band. In some embodiments, the length of the coaxial polarizer corresponds to properties of a material forming the coaxial polarizer and a shape of the coaxial polarizer. The coaxial polarizer may include a portion having a notched rectangular shape. 
     The coaxial OMT further can include at least two ports disposed at a predetermined distance from each other. The predetermined distance may correspond to a return loss threshold and an isolation threshold of the reflector antenna. 
     The feed assembly may include a matching section coupled to the feed horn that is common to the low, mid and high frequency bands. A polarizer can be disposed in the center conductor of the feed assembly, the polarizer common to the mid and high frequency bands. The feed assembly can include a diplexer configured to separate a first and second port for mid frequency bands from a third port for high frequency bands. 
     In an embodiment, the respective beamwidths (e.g., 10-dB beamwidths) for the low, mid and high frequency bands is approximately equal. For example, the respective 10-dB beamwidths can be about 74 degrees. The feed assembly can include a co-located phase center for launching signals in the low, mid and high frequency bands. 
     In another aspect, a method is provided comprising receiving and transmitting signals using a feed assembly for a reflector antenna at low, mid and high frequency bands, providing a feed horn common to the low, mid and high frequency bands, launching signals in the low frequency band using a coaxial polarizer and a coaxial orthomode transducer (OMT), and launching signals in the mid and high frequency band using a polyrod and a diplexer, wherein the polyrod and the diplexer support the low frequency band. 
     The method may include providing the coaxial polarizer at a length that corresponds to one-half a wavelength of an operating frequency in the low frequency band. In some embodiments, the length of the coaxial polarizer corresponds to properties of a material forming the coaxial polarizer and a shape of the coaxial polarizer. 
     A portion of the coaxial polarizer can be formed having a notched rectangular shape. First and second ports can be disposed at a predetermined distance corresponding to a return loss threshold and an isolation threshold of the reflector antenna. 
     In some embodiments, a polarizer can be provided in a center conductor of the feed assembly. The polarizer can be common to the mid and high frequency bands. The diplexer can be configured to separate first two ports for mid frequency bands from a third port for high frequency bands. 
     The respective 10-dB beamwidths for the low, mid and high frequency bands can be approximately equal. In some embodiments, the respective beamwidths are about 74 degrees. The feed assembly can be configured to have a co-located phase center for launching signals in the low, mid and high frequency bands. 
     The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cut-away view of a tri-band feed assembly; 
         FIGS. 1A-1B  are two isometric views of the tri-band feed assembly of  FIG. 1 ; 
         FIG. 2  is a cut-away view of two coaxial polarizers and a coaxial orthomode transducer (OMT) of the tri-band feed assembly of  FIG. 1 ; 
         FIGS. 2A-2B  are cut-away views of the coaxial polarizer of the tri-band feed assembly of  FIG. 1 ; 
         FIGS. 2C-2D  are isometric views of the coaxial OMT of the tri-band feed assembly of  FIG. 1 ; 
         FIGS. 2E-2F  are cut-away views of the OMT of the tri-band feed assembly of  FIG. 1 ; 
         FIG. 2G  is a cut-away view of a center conductor disposed within the coaxial OMT of the tri-band feed assembly of  FIG. 1 ; 
         FIGS. 3-3B  are different views of the tri-band feed assembly of  FIG. 1  coupled to a reflector antenna; and 
         FIG. 4  is a flow diagram of a method for receiving and/or transmitting signals using the tri-band feed assembly of  FIG. 1 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Described herein is a tri-band feed assembly for that operates at multiple different frequency bands (e.g., low, mid and high frequency bands) that can be utilized in various satellite communications (SATCOM) applications, such as reflector antenna applications. In embodiments, the tri-band feed assembly comprises multiple portions having smaller (or compact) dimensions as compared with similar components of other feed assemblies known in the art. Thus, the tri-band feed assembly can be applied in small or low profile reflector antenna applications, such as but not limited to, airborne, shipboard or ground mobile platforms having limited real estate. The different components of the tri-band feed assembly can be configured to support one or more different frequency bands such that the respective beamwidths for the different frequency bands are approximately equal and maintain a common phase center for each of the different frequency bands. 
     In embodiments, the low, mid, and high bands that make up the tri-bands of the feed include K (20.2-21.2 GHz), Ka (30-31 GHz), and Q (43.5-45.5 GHz) bands, respectively. It should be appreciated that while a tri-band feed is described herein, it is understood that additional frequency bands can use one or components of the tri-band feed assembly described herein. The terms “common” and “support” can refer to the ability of a component of the feed assembly to perform an operation on, receive and/or transmit signals in the respective frequency band. In some embodiments, an operation may include conveying or transitioning signals to other components in the feed assembly. Components of the feed assembly may include, but not limited to, a feed horn, matching section, coaxial polarizer, coaxial OMT, polarizer, diplexer and center conductor. 
     Referring now to  FIG. 1 , a tri-band feed assembly  100  includes a feed horn  102 , a matching section  104 , a coaxial polarizer  106 , a coaxial orthomode transducer (OMT)  108 , a polyrod  110 , a polarizer  112 , and a diplexer  114 . In the illustrative embodiment, the low, mid, and high bands that make up the tri-bands of the feed include K (20.2-21.2 GHz), Ka (30-31 GHz), and Q (43.5-45.5 GHz) bands, respectively. 
     Feed horn  102  may be coupled to a reflector antenna (not shown, such as reflector antenna  302  of  FIG. 3 ). In an embodiment, feed horn  102  can receive signals from the reflector antenna and convey the signals to other components within feed assembly  100 . Feed horn  102  can include a tri-band feed horn and can be configured to receive and transmit signals at low, mid and high frequency bands. 
     Matching section  104  may be disposed in an inner cavity/channel of feed horn  102 . In an embodiment, matching section  104  may include a dielectric ring sandwiched between two metallic iris rings to provide impedance matching between the feed and free space where the transmitted signal is radiated into or the received signal is coming from. Matching section  104  is configured to support each of the low, mid and high frequency bands. 
     Coaxial polarizer  106  is disposed within an inner cavity of feed assembly  100  and is configured to launch signals in a low frequency band. In some embodiments, one or more coaxial polarizers are coupled to a center conductor  116  disposed in the inner cavity of feed assembly  100 . Coaxial polarizer  106  can have a length of one-half a wavelength of frequencies (e.g., operating frequency) in the low frequency band. The length can correspond to properties of a material forming the coaxial polarizer and a shape of the coaxial polarizer. Coaxial polarizer  106  will be described in greater detail with respect to  FIGS. 2-2A  below. 
     Coaxial OMT  108  is coupled to feed horn  102  and can be disposed around center conductor  116  and coaxial polarizer  106 . Coaxial OMT  108  can include one or more ports (here one port  124  is shown) to launch signals in the low frequency band. In some embodiments, the ports may include left-hand and/or right-hand circular polarization ports. Coaxial OMT  108  can be formed having a compact shape such that the ports can be disposed at a reduced distance from each. The reduced (or predetermined) distance can be selected based at least in part on a return loss threshold and an isolation threshold of the reflector antenna. Coaxial OMT  108  may include a pair of shorting fins that are used to provide additional isolation between the two orthogonal ports. In each of the two orthogonal ports, a wedge section is used to provide compact transition from the coaxial waveguide to rectangular waveguide, which also serves as a matching section for the transition. Coaxial OMT  108  will be described in greater detail with respect to  FIGS. 2 and 2C-2D  below. 
     Polyrod  110  is disposed within center conductor  116 . In the illustrative embodiment of  FIG. 1 , polyrod  110  is disposed within a first (end) portion  116   a  of center conductor  116  such that a first end  110   a  extends into feed horn  102  to launch the signal from center conductor  116  and a second end  110   b  is disposed proximate to polarizer  112 . The second end  110   b  can be started within a taper circular waveguide section that reduce the diameter with dielectric loading provided by the polyrod. In an embodiment, this dielectric loading can be utilized to support proper inner diameter for the coaxial waveguide. Polyrod  110  can be configured to launch signals in mid and high frequency bands. 
     Polarizer  112  is disposed within a second (middle) portion  116   b  of center conductor  116 . Polarizer  112  can be configured to launch signals in mid and high frequency bands. Polarizer  112  can be configured to convert a linearly polarized wave into a circular polarized wave, or a circular polarized wave into a linearly polarized wave. Polarizer  112  can be configured to apply a phase differential or a phase shift (e.g., 90° phase shift) for the conversion. Polarizer  112  can be configured to launch signals in mid and high frequency bands. 
     Diplexer  114  is can be disposed proximate to polarizer  112  and can be configured to launch signals in mid and high frequency bands. In an embodiment, a third (end) portion  116   c  of center conductor  116  can disposed within and extend through diplexer  114 . As is known in the art, a waveguide diplexer is a device for combining/separating multi-band and multi-port signals to provide band or polarization discrimination. Diplexer  114  can include one or more ports to separate mid band ports and high band ports to launch signals in the respective frequency bands. For example, and as illustrated in  FIG. 1 , diplexer  114  can include first two ports  120  (although one port is shown for clarity) for signals in the mid frequency band and a third port (e.g., second port  122  of  FIG. 1B ) for signals in the high frequency band. It should be appreciated that the number of ports and properties of the diplexer can based at least in part on a particular application of feed assembly  100 . For example, in one embodiment, diplexer may include a four-port diplexer to separate two mid-band ports and two high-band ports. 
     Briefly referring to  FIGS. 1A-1B , alternate views of feed assembly  100  are provided illustrating the entire feed assembly coupled together (i.e., two portions of feed assembly  100  coupled together). As illustrated in  FIGS. 1A-1B , feed horn  102 , coaxial OMT  108  having a port  126 , and diplexer  114  having a first port  120  (e.g., mid band port) and a second port  122  (e.g., high band port) are shown. Matching section  104 , coaxial polarizer  106 , polyrod  110 , polarizer  112  and center conductor  116  are not shown in  FIGS. 1A-1B , as they are disposed within an inner cavity of feed assembly  100 . 
     Referring now to  FIGS. 2-2C , a first coaxial polarizer  202   a  and a second coaxial polarizer  202   b  are coupled to a coaxial OMT  204  having a first OMT port  206  and a second OMT port  208 . Coaxial polarizers  202   a ,  202   b  and coaxial OMT  204  may be the same or substantially similar to coaxial polarizer  106  and coaxial OMT  108  of  FIG. 1 , respectively. 
     First and second coaxial polarizers  202   a ,  202   b  and coaxial OMT  204  can be provided having compact dimensions as compared with other polarizers and OMTs known in the art. In embodiments, a length of each of first and second coaxial polarizers  202   a ,  202   b  can be approximately one-half a wavelength at frequencies (e.g., operating frequency) in the low frequency band. The reduced length can be based at least in part on a shape of the respective coaxial polarizer  202   a ,  202   b  and/or properties of the material forming the respective coaxial polarizer  202   a ,  202   b . For example, a vain polarizer, as is known in the art, can utilize taper shape to provide good impedance matching while slow down the E-field to provide 90-degree phase shift. However, first and second coaxial polarizers  202   a ,  202   b  (and other polarizers include a notched region (and other polarizers described herein having a notched shape or notched region). The notched shape can provide sufficient phase shift and/or good matching within a polarizer of a shorter length, as compared to a polarizer not having a notched shape. It should be appreciated that with the same length, the notched regions can have more dielectric material than, for example, a tapered section. Thus, the overall length of first and second coaxial polarizers  202   a ,  202   b  can be reduced by including one or more notched regions. Further, first and second coaxial polarizers  202   a ,  202   b  can include high-k dielectric material having a high dielectric constant (e.g., Hi-K material) to further shorten their respective lengths from other types of vane polarizers having material such as Rexolite or Teflon with a dielectric constant from 2.1 to 2.54. 
     For example, and now referring to  FIGS. 2A-2B , coaxial polarizer  202 , which is the same as first and second coaxial polarizers  202   a ,  202   b  of  FIG. 2 , is illustrated having a rectangular shape and includes a first portion  210   a , second portion  210   b  and a third portion  210   c . The first and third portions  210   a ,  210   c  (or end portions) can include notched regions (or notched rectangular regions)  212   a ,  212   b  respectively. Second portion  210   b  (or middle portion) can be formed in a generally rectangular shape and couple first and third portions  210   a ,  210   c . In an embodiment, the shape of notched regions (i.e., the notched shape) of first and second coaxial polarizers  202   a ,  202   b  can provide sufficient phase shift and good matching with a shorter length than a polarizer not having a notched shape. 
     Coaxial polarizer  202  can include one or more materials having a high dielectric constant, such as but not limited to high-k dielectric material having a high dielectric constant (e.g., Hi-K material). 
     Now referring to  FIGS. 2C-2D , different views of coaxial OMT  204  are provided without ports attached (e.g., first port  206  and second port  208  of  FIG. 2 ). As illustrated in  FIG. 2B , coaxial OMT  204  includes a first cavity  212 , a second cavity  214  and a hollow region  216  formed within and extending a length of coaxial OMT  204 . First cavity  212  and second cavity  214  can be configured to couple with and receive a port, such as first port  206  and second port  208  of  FIG. 2 . In an embodiment, first cavity  212  and second cavity  214  can be communicatively coupled with hollow region  216  to transmit and receive signals in the low frequency band. 
     Now referring to  FIGS. 2E-2F , a first half  204   a  and a second half  204   b  of coaxial OMT  204  are shown. Each of first and second halves  204   a ,  204   b  include a half of first cavity  212  to couple with and receive a first port (e.g., first port  206  of  FIG. 2 ) and a half of second cavity  214  to receive a second port (e.g., second port  208  of  FIG. 2 ). First and second halves  204   a ,  204   b  further include a half of hollow region  216  (here having a generally cylindrical shape), such that when first and second halves  204   a ,  204   b  are coupled together hollow region  216  of  FIGS. 2C-2D  is formed. Hollow region  216  can be configured to hold a center conductor of the feed assembly. For example, and as illustrated in  FIG. 2G , a center conductor  220  can be disposed within hollow region  216  of coaxial OMT  204 . First and second coaxial polarizers  202   a ,  202   b  are coupled to an outer surface of center conductor  220 . 
     Now referring back to  FIG. 2 , coaxial OMT  204  can be formed such that first port  206  and second port  208  are disposed at a predetermined distance from each other. The predetermined distance can be based at least in part on a return loss threshold and an isolation threshold of a reflector antenna coaxial OMT  204  is coupled to. In one embodiment, the overall length of coaxial OMT  204  can be approximately 1.75 wavelengths at low band and separation between two ports (i.e., first and second ports  206 ,  208 ) can be less than 0.4 wavelength. However, it should be appreciated that the overall length of coaxial OMT  204  and separation between two ports can vary based at least in part on the requirements of a particular application. 
     Referring now to  FIGS. 3-3B , different views of a reflector antenna  302  coupled to a feed assembly  306  are shown. Feed assembly  306  includes a feed horn  308 , matching section  310 , coaxial polarizer  312 , coaxial OMT  314 , a polyrod  316 , a polarizer  318 , a diplexer  320 , and a center conductor  322 . Feed assembly  306  may be the same as or substantially similar to feed assembly  100  of  FIG. 1 . 
     Feed assembly  306  can be coupled to reflector antenna  302  to provide a tri-band feed such that reflector antenna  302  can transmit and/or receive signals in multiple frequency bands, such as low, mid and high frequency bands. In an embodiment, feed assembly  306  can be configured to have a common phase center for each of the different frequency bands and achieve high phase efficiencies for the reflector antenna  302  for all three bands. Feed assembly  302  can have equal or substantially equal beamwidths for each of the different frequency bands. In some embodiments, the 10-db beamwidths for the different frequency bands can be approximately 10 dB can be about 74 degrees. 
     Referring now to  FIG. 4 , a flow diagram of a method  400  for receiving and/or transmitting signals using the tri-band feed assembly  100  of  FIG. 1 , begins at block  402  by receiving and transmitting signals using a feed assembly for a reflector antenna at low, mid and high frequency bands. The feed assembly can be coupled to the reflector antenna and be configured to support signals in each of the low, mid and high frequency bands (e.g., low—K (20.2-21.2 GHz), mid—Ka (30-31 GHz), and high—Q (43.5-45.5 GHz) bands). 
     At block  404 , a feed horn common to the low, mid and high frequency bands can be provided. The feed assembly can include a feed horn that couples with the reflector antenna. The feed horn can be configured to launch signals in each of the low, mid and high frequency bands and thus convey (or transmit) signals received by the reflector antenna to other components within the feed assembly. 
     A matching section is coupled to the feed horn. The matching section can be configured to process signals in each of the low, mid and high frequency bands and convey them to a coaxial polarizer and coaxial OMT of the feed assembly. 
     At block  406 , signals in the low frequency band can be launched using the coaxial polarizer and the coaxial OMT. The coaxial polarizer can apply a phase differential to a received signal to perform polarization conversion. 
     In some embodiments, one or more coaxial polarizer can be disposed on an outer surface of a center conductor. The coaxial polarizers and the center conductor can be disposed within an inner cavity of the coaxial OMT. The coaxial OMT can include multiple ports to launch signals in the low frequency bands. For example, in some embodiments, the coaxial OMT can include a first port for signals having left hand circular polarization properties and a second port for signals having right hand circular polarization properties. 
     At block  408 , signals in the mid and high frequency bands can be launched using a polyrod and a diplexer. Signals having frequencies corresponding to the mid or high frequency bands be received at the polyrod. The polyrod can be disposed in the center conductor of the feed assembly such that a first end extends to the feed horn to receive the signals and a second end is disposed in a generally middle portion of the center conductor to convey the signals to other components (e.g., polarizer, diplexer) in the feed assembly. Each of the first and second end of the polyrod can include a tapered portion. The tapered portions of the polyrod can provide a gradual impedance change to minimize mismatch for both mid and high frequency bands. Thus, the polyrod can be configured to support signals in the mid and frequency band and convey them to a polarizer. 
     The polarizer can be configured to support signals in the mid and frequency bands and convey them to the diplexer. The diplexer can include multiple ports to separate signals in the mid frequency band from signals in the high frequency band. In some embodiments, the diplexer can include at least one mid band output port and at least one high band output port. The mid band output port can launch signal in the mid frequency band and the high band output port can launch signal in the high frequency band. 
     The feed assembly supports and launches signal in each of the low, mid and high frequency bands by including a portion for low frequency band signals and a portion for mid and high frequency band signals. For example, and as described herein, the coaxial polarizer and coaxial OMT can be configured to launch signals in the low frequency band and the polyrod, polarizer and diplexer can be configured to launch signals in the mid and high frequency bands. Thus, the feed assembly is a tri-band feed assembly. 
     Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent that other embodiments incorporating these concepts, structures and techniques may be used. Accordingly, it is submitted that the scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims. 
     Accordingly, other embodiments are within the scope of the following claims.