Patent Publication Number: US-7898491-B1

Title: Reflector antenna feed RF seal

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates to microwave reflector antennas. More particularly, the invention relates to a Radio Frequency (RF) seal for the joint between the feed and main reflector/antenna base of a reflector antenna. 
     2. Description of Related Art 
     Self supported feed assemblies typically include a subreflector supported proximate a focal point of the main reflector by a feed waveguide coupled to a mounting hub fastened to an antenna base that also supports the main reflector. A joint between the main reflector/antenna base and the mounting hub creates an RF leakage path to the rear of the reflector antenna that generates signal backlobes known to degrade the reflector antenna signal pattern. A vertex plate is commonly applied to the proximal end of the feed waveguide and/or mounting hub to improve the overall return loss of the antenna. 
     Prior reflector antennas typically apply a plurality of conductive seal(s), such as a spring ring(s) and/or conductive grease, to seal the joint and/or area between the vertex plate and the main reflector/antenna base. Conductive grease application is time-consuming and may be difficult for installation personnel to correctly apply in exposed reflector antenna mounting environments, such as high atop radio towers. Also, conductive grease application may require skin protection for the installation personnel, further complicating application. 
     Competition in the reflector antenna market has focused attention on improving electrical performance and minimization of overall manufacturing, inventory, distribution, installation and maintenance costs. Therefore, it is an object of the invention to provide a reflector antenna feed assembly mounting hub joint seal that overcomes deficiencies in the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, where like reference numbers in the drawing figures refer to the same feature or element and may not be described in detail for every drawing figure in which they appear and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic exploded isometric partial cut-away view of a reflector antenna feed hub/antenna base joint RF seal. 
         FIG. 2  is a schematic isometric partial view of  FIG. 1 , with the feed hub coupled to the antenna base. 
         FIG. 3  is a schematic partial back view of  FIG. 2 . 
         FIG. 4  is a schematic side section view of  FIG. 3 , along line A-A. 
         FIG. 5  is a close-up view of area B of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have developed a cavity conforming conductive and/or RF absorbent compressible gasket arrangement that eliminates the prior requirement for multiple RF seals and/or application of conductive grease, significantly reducing manufacture and assembly requirements for a reflector antenna. 
     A first exemplary embodiment is demonstrated in  FIGS. 1-5 . As best shown in  FIG. 1 , the main reflector  3  is coupled to the antenna base  5 . The antenna base  5  is adapted to receive a feed hub  7  supporting the feed waveguide  9  and subreflector  11 , forming a joint  13  upon assembly. A vertex plate  15  at the proximal end of the feed waveguide  9  has a diameter greater than a periphery of the joint  13 . A generally annular gasket  17  is adapted to seat between an outer surface of the feed hub  7 , the vertex plate  15  and the antenna base  5 . 
     The gasket  17  may be provided as a portion of compressible material with an outer diameter greater than at least a periphery of the mating surfaces between the feed hub  7  and the antenna base  5  and lesser than the outer diameter of the vertex plate  15 . For ease of initial assembly, the gasket  17  may be dimensioned for retention in a stretch fit around the outer surface of the feed hub  7 . Upon insertion of the feed hub  7  into the antenna base  5 , the gasket  17  is compressed within a cavity between the vertex plate  15 , feed hub  7  and antenna base  5 , for example via tightening of fasteners such as screws or bolts (not shown) extending through the antenna base  5  into mounting hole(s)  19  of the feed hub  7 . 
     The gasket  17  may be formed from a compressible conductive and/or RF absorbent material. Alternatively, the gasket  17  material may be a compressible media coated with RF absorbent material and/or conductive material. An example of a suitable compressible material coated with an RF absorbent is urethane foam with a gradient lossy coating such as C-Ram AR, by Cuming Microwave, of Avon Mass., USA. The gasket  17  may be cost effectively formed by cutting or stamping gasket(s)  17  of desired dimensions out of bulk sheets of the selected material. 
     The compression of the gasket  17  form fills the cavity between the outer diameter of the feed hub  7 , the vertex plate  13  and the antenna base  5 , as best shown in  FIG. 5 , sealing the joint  13  against RF leakage. Further, where a junction  23  between the main reflector  3  and the antenna base  5  has an outer diameter less than the outer diameter of the gasket  17 , the junction  23  is also sealed by the gasket  17 . 
     The compression of the gasket  17  may be primarily in a direction parallel to a longitudinal axis of the feed, reducing deformation of the gasket  17  in a direction normal to the longitudinal axis such that the gasket  17  does not extend beyond the diameter of the vertex plate  13  when compressed. 
     One skilled in the art will appreciate that, in addition to improving the electrical performance of the assembled reflector antenna, the gasket  17  arrangement also enables significant manufacturing, delivery, installation and/or maintenance efficiencies as manufacture, inventory, delivery and assembly of multiple conventional point sealing gaskets and/or conductive grease are eliminated. 
     
       
         
           
               
             
               
                   
               
               
                 Table of Parts 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 3 
                 main reflector 
               
               
                 5  
                 antenna base 
               
               
                 7 
                 feed hub 
               
               
                 9 
                 feed waveguide 
               
               
                 11 
                 subreflector 
               
               
                 13 
                 joint 
               
               
                 15 
                 vertex plate 
               
               
                 17 
                 gasket 
               
               
                 19 
                 mounting hole 
               
               
                 23 
                 junction 
               
               
                   
               
            
           
         
       
     
     Where in the foregoing description reference has been made to materials, ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth. 
     While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant&#39;s general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.