Patent Publication Number: US-6700548-B1

Title: Dual band antenna feed using an embedded waveguide structure

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to dual band antenna feeds for combining two or more different frequency antenna feeds to connect to a single antenna. 
     2. Related Art 
     The dual band antenna feeds are usually designed by connecting two waveguide ports carrying signals over two separate frequency bands to a common waveguide structure which connects to an antenna operating over both bands. As illustrated in block diagram form in FIG. 1, a conventional antenna feed receives a first high frequency band of signals at input  2 . The second lower frequency band is received at input  4 . A filter  6 , which may be a low pass, band pass, or band stop filter removes higher frequency components from the low frequency input  4  to prevent interference with signals from the high frequency input  2 . Cavity-type filters are used as filter  6  to connect the waveguide ports to the common waveguide and avoid interference between the two frequency bands. Since a filter is a frequency sensitive device, its cost is high due to the tight tolerance and tuning requirements. A common junction  8  combines the signals from ports  2  and  4  to provide an output for an antenna  10 . 
     SUMMARY 
     The present invention provides a dual band antenna feed using an embedded waveguide structure made without requiring an added cavity-type filter. The dual band antenna feed of the present invention is made amenable to die-casting. 
     The dual band antenna feed in accordance with the present invention, referring to FIG. 2, includes a Ka and Ku band interface section  22 . The interface section  22  has signals fed from a orthogonal mode transducer (OMT) and power combiner section  20 . The output of the Ka and Ku band interface section  22  is provided to an antenna section  24 . 
     The Ka and Ku band interface section  22 , referring to FIGS. 3A-3D, includes two Ka band vertical polarization waveguide sections  31  and  32 , and a single Ku band waveguide section  34  which carries both vertical and horizontal polarization Ku band signals. The opposing walls  36 - 37  of the Ku band waveguide  34  carrying the vertical polarization Ku band signals are transitioned to step down from an input section  40  to successively smaller dimensioned sections  41 - 44 , and then to step back up in successively larger dimensioned sections  45 - 47  to an output section  48 . The two Ka band sections  31 - 32  are fed into openings in the combined Ka/Ku band section  46 , on opposite sides of the opening for the Ku band transition section  45 . A slightly larger Ka/Ku band section  47  then transitions from section  46  to the output section  48 . The output section  48  provides a combined Ka band vertical and Ku band horizontal and vertical signals. The output section  48  connects to the separate antenna section ( 24 ). With the Ka-band waveguides  31 - 32  having ports  56 - 57  facing the antenna port for radiation on opposite sides of the Ku-band section  45  port, sufficient isolation will be provided between the Ka and Ku band signals without requiring an additional filter. 
     The OMT and power combiner section  20  can have components as shown in FIGS. 4A-4D. The OMT  90  is a conventional device with separate Ku band vertical and horizontal polarization inputs  12  and  14  which combines the inputs to produce a single output carrying both the vertical and horizontal polarization Ku band signals. The power combiner has a first input ( 16 ) for receiving the Ka band vertical polarization signal, and functions to split the input into two separate signals provided in two separate Ka band vertical polarization waveguides  81 - 82 . 
     The Ka and Ku band interface section  22  can be manufactured from a single block of stock metal. The stock metal block is first cut into two halves, and the Ka band waveguides are machined into the halves. The two halves are then each cut in half to form a total of four quarter sections. The Ku band waveguide is then machined into the quarter sections, and the quarter sections are reassembled to form the completed interface section  22 . The quarter sections can be used to form molds which are then used for die casting to enable rapid manufacturing of multiple interface sections  22 . 
     In one embodiment, the antenna feed can include a dielectric insert as shown in FIGS. 8A-8C. The dielectric insert includes Ka band inserts  110  and  111  which insert into Ka band sections  31  and  32  to improve matching between the Ka band sections  31  and  32  and combined Ka/Ku band section  46 . A notch  114  is further included to improve the match between the Ku band section  45  and combined Ka/Ku band section  46 . The insert has a rectangular portion  106  which transitions into a tapered conical section  108  which extends into the antenna portion  24  of the antenna feed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Further details of the present invention are explained with the help of the attached drawings in which: 
     FIGS. 1 show a block diagram of components of a conventional dual-band antenna feed; 
     FIG. 2 shows a perspective view of exterior and interior portions of an antenna feed assembly in accordance with the present invention; 
     FIGS. 3A-3D show cutaway and end views of a Ku and Ka band interface  22  section of the antenna feed of FIG. 2; 
     FIGS. 4A-4D show cutaway and end views of the OMT and power combiner section  20  of the antenna feed of FIG. 2; 
     FIGS. 5A-5B show a cutaway and a front view of the antenna section  24  of the antenna feed of FIG. 2; and 
     FIGS. 6A-6B show a cutaway and a front view of an alternative conical antenna usable as the antenna portion  24  of the antenna feed of FIG. 2; and 
     FIGS. 7A-7E, illustrate cuts made in stock metal to enable manufacturing of an embodiment of the antenna feed of the present invention. 
     FIGS. 8A-8C illustrate a dielectric insert which can be provided as part of the antenna feed of the present invention for improved performance. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 shows an antenna feed in accordance with the present invention. The antenna feed has four ports: Ku-band vertical polarization  12 , Ku-band horizontal polarization  14 , Ka-band vertical polarization  16 , and the antenna port  18 . The ports  12  and  14  are indicated as being Ku-band, while the port  16  is indicated as being Ka band for purposes of illustration. Other bands may be used in accordance with the present invention. 
     The antenna feed of FIG. 2 can be considered as three separate sections  20 ,  22  and  24 . A first section  20  is a combined orthogonal mode transducer (OMT) and power combiner, which is shown in more detail in FIGS. 4A-4D. The OMT portion combines signals from the horizontal and vertical polarization Ku band inputs  12  and  14 . The power combiner portion splits the Ka vertical band signal received at port  16  into two separate waveguides. The combined OMT and power combiner  20  is described in more detail with reference to FIGS. 4A-4D to follow. 
     The second section  22  is a Ku and Ka band interface, which is shown in more detail in FIGS. 3A-3D. The Ku and Ka band interface  22  is configured to direct the Ku and Ka band signals from the combined OMT and power combiner section  20  to form a single combined signal for launching at an antenna connection port. The Ku and Ka band interface section  22  is described in more detail with reference to FIGS. 3A-3D to follow. 
     The third section  24  is the antenna for connecting to the Ku and Ka band interface section  22 . The antenna section  24  shown in FIG. 2 is described in more detail with reference to FIGS. 5A-5B. An alternative conical shaped antenna may be used in place of antenna  24 , and is described with reference to FIGS. 6A-6B to follow. 
     FIGS. 3A-3D show cutaway and end views of a Ku and Ka band interface  22  section of the antenna feed of FIG.  2 . The Ku and Ka band interface section  22  includes two rectangular Ka band waveguides  31 - 32 . The two Ka band waveguides  31 - 32  are fed from two similar waveguides in the combined OMT and power combiner  20 , as described in more detail to follow with regard to FIGS. 4A-4D. 
     The Ku and Ka band interface section  22  further includes a single Ku band waveguide  34  for carrying both Ku vertical and horizontal polarization signals. The Ku band waveguide  34  includes a square input section  40 . From the square input section  40 , the opposing waveguide walls  36 - 37  carrying the vertical polarization signals are transitioned in steps  41 - 44  down to a minimum size and then back in steps  45 - 47  to a section  48 . Section  48  is the size of the square input section  40 , and forms the output of the Ku band waveguide  34 . The opposing waveguide walls  38 - 39  carrying the horizontal polarization signals remain the same dimension from the input section  40  through transitions  41 - 47  to the output section  48 . 
     The Ka band waveguides  31 - 32  are routed from initial points  51  and  52  spaced laterally a slight distance from respective opposing vertical waveguide walls  36 - 37  of the initial section  40  of the Ku band waveguide  34  to final points  54  and  55  spaced a slight distance from respective opposing vertical waveguide walls of the transition section  45 . The Ka band waveguides  31 - 32  are then terminated in openings  56  and  57  in the Ka/Ku band section  46 . By terminating the Ka band waveguides  31 - 32  in openings  56  and  57  in the Ka/Ku band section  46 , the Ka band signals are launched and combined with the Ku band signals in section  46 . The combined Ku and Ka band vertical polarization signals are then transitioned using section  47  to the square waveguide output section  48 . The output section  48  of the Ku and Ka band interface provides a connection to the antenna section  24 . 
     Since the openings  56  and  57  of the Ka-band waveguides  31  and  32  are facing the antenna port for radiation and provided on opposite sides of the Ku-band port of section  45 , there will be sufficient isolation even without a filter. Thus a filter, such as filter  6  of FIG. 1, provided between the Ku band input and the common junction at section  46  with the higher frequency Ka band signals is unnecessary. 
     The two separated Ka-band waveguides  31 - 32  are used instead of a single waveguide launch into section  46  to excite symmetrical modes. The symmetrical modes enable an antenna beam created from a signal at the output section  48  to be aligned with the physical center of the antenna section  24 . 
     As shown in FIGS. 3A-3D, Ku and Ka band interface section  22  includes six tuning stubs  61 - 66  on the initial section  40 , and another six tuning stubs  71 - 76  on the output section. The tuning stubs help optimize the performance of the Ku and Ka band interface section  22  by minimizing reflections or return losses. Although shown with tuning stubs located in the areas illustrated, it is understood that the tuning stubs might be located at other areas without significantly degrading performance. Likewise, the tuning stubs may be eliminated without a significant degradation in performance, depending on desired performance. 
     FIGS. 4A-4D show cutaway and end views of the OMT and power combiner section  20  of the antenna feed of FIG.  2 . As indicated above the OMT and power combiner of FIGS. 4A-4D includes a single Ka band input  16  and a power combiner  80  (or power splitter) which transitions the single Ka band input  16  into two Ka band waveguide portions  81 - 82  which are routed around an ortho-mode transducer (OMT)  90  to provide Ka band waveguide outputs  84 - 85  for connection to matching waveguide sections  31 - 32  in the Ka and Ku band transition section  22 . Note that labels to similar items, such as Ka band input  16 , are carried over from FIG. 2 to FIG.  4 . Labels for items carried forward will likewise be similarly labeled in other subsequent drawings. 
     The OMT  90  is a conventional device and includes the vertical polarization Ku band input  12  and the horizontal polarization Ku band input  14 . The vertical and horizontal polarization signals from inputs  12  and  14  are combined by the OMT  90  into a single square waveguide section  92  which supports both horizontal and vertical polarizations. The square waveguide section  92  mates with the similar square wave guide section  40  of the Ku and Ka band interface section  22  shown in FIGS. 3A-3D. 
     FIGS. 5A-5B show a cutaway and a front view of the antenna section  24  of the antenna feed of FIG.  2 . As shown the antenna section  24  includes a square waveguide  94  matching the dimensions of the square waveguide output section  48  of the Ku and Ka band interface section  22 . One port  95  of the square waveguide  94  mates with the Ku and Ka band interface section  22 , while a second port  18  forms the antenna output  18 . 
     FIGS. 6A-6B show a cutaway and a front view of an alternative conical antenna usable as the antenna portion  24  of the antenna feed of FIG.  2 . The conical antenna of FIGS. 6A-6B provides one alternative to simply using the square waveguide of FIGS. 5A-5B, although other antennas may be used depending on desired design and performance requirements. The conical antenna of FIGS. 6A-6B will typically provided decreased return losses and a lower VSWR than the square waveguide of FIGS. 5A-5B. The antenna section of FIGS. 6A-6B includes a square waveguide portion making up a first port  98  for mating with the square waveguide output section  48  of the Ku and Ka band interface section  22 . The antenna section then includes a conical shaped transition section for transitioning from the first square port  98  to a second larger round port  18  which forms the antenna output. A part of the exterior  98  of the antenna portion  24  is also machined to form a conical shape feed horn to improve antenna performance. 
     FIGS. 7A-7E illustrate cuts to make in stock metal to enable manufacturing of all of sections  20 ,  22  and  24  combined as a single unit. For such manufacturing, a solid stock metal block sized to form the entire assembly of sections  20 ,  22  and  24  is used. Assuming that a conical antenna portion  24  is used as illustrated in FIGS. 6A and 6B, both the inside and outside portion of the conical horn is initially machined using a lathe. Next, the metal block is cut in half longitudinally along line  100  as illustrated in FIG.  7 A. Next a deep double ridge is cut into each half so that when the halves are reassembled the Ka band waveguides  31 ,  32 ,  81  and  82  are formed. With the halves reassembled, another longitudinal cut  102  is made to cut the stock metal block into quarters as illustrated in FIG.  7 A. The four quarter sections are then machined with the additional Ku band waveguide and combined Ku and Ka band waveguide portions as shown in FIGS. 7B-7E. The four quarter sections of FIGS. 7B-7E are then reassembled to form the completed unit. 
     Once machined, the quarter sections of FIGS. 7B-7E can be used for form casts so that molds may be made to allow die casting. Die cast sections can be manufactured at a low cost relative to machined sections. Note that although the entire assembly of sections  20 ,  22  and  24  are illustrated as being manufactured together, the individual sections may be manufactured in a similar manner by matching quarter sections, and then assembling the quarter sections to form a completed unit. 
     FIGS. 8A-8C illustrate a dielectric insert which can be provided as part of the antenna feed of the present invention for improved performance. FIG. 8A shows a perspective view of the dielectric insert. FIG. 8B shows a side view of the dielectric insert, and FIG. 8C shows a back view. The dielectric insert includes Ka band insert portions  110  and  111  which are designed to extend into the Ka band waveguide portions  31  and  32  at respective ends  54  and  55 . The Ka band insert portions  110  and  111  preferably extend a distance ¼ λg of the Ka band waveguide into sections  31  and  32  to improve matching between the Ka band waveguides  31  and  32  and the combined Ka/Ku band waveguide section  46 . 
     The dielectric insert further includes a rectangular portion  106  with dimensions preferably matching the Ka/Ku band section  46 . The rectangular section  106  then extends through sections  47  and  48 , transitioning into a conical tapered section  108 . The conical tapered section  108  extends into the antenna portion  24  and preferably terminates at a point prior to the antenna opening  18 . The dielectric insert provides improved antenna performance for either the waveguide antenna shown in FIGS. 5A and 5B, or the conical antenna shown in FIGS. 6A and 6B. 
     The dielectric insert in one embodiment further includes a notch  114  cut into the rectangular section  106  for the purpose of matching and reducing the backward wave of a Ka band signal. The notch  114  has a height dimension h and a width dimension w. The height dimension h is preferably ¼ λg at Ka band. This notch produces another backward wave  180  degrees out of phase to cancel the original residue backware wave. This minimizes the Ka band backward wave. The width dimension w is adjusted to a desired value to maximize performance of the antenna feed over the desired bandwidth of operation. The tapered conical portion  108  is tapered to minimize reflections of signals launched from the antenna portion  24 . 
     The dielectric insert can be manufactured from a desired material such as Nylon or Teflon if a low dielectric constant is desired, or from other materials if a higher dielectric constant is desired. For manufacturing the stock material is simply machined into the shape shown in FIG.  8 A. The dielectric insert is securely attached to the antenna feed by applying an adhesive material to the Ka band inserts  110  and  111 , and to the rectangular portion  106  which contacts the walls of the Ka/Ku band section  46 . 
     Although the present invention has been described above with particularity, this was merely to teach one of ordinary skill in the art how to make and use the invention. Many additional modifications will fall within the scope of the invention, as that scope is defined by the claims which follow.