Abstract:
A coaxial connector is combined with an inner conductor interconnection cap, for interconnection with a coaxial cable. The interconnection cap is provided with a bore adapted to seat upon and circumferentially contact an outer diameter of the inner contact and an outer diameter of the inner conductor. The interconnection cap extends along the inner contact to cover at least a contact portion at a cable end of the inner contact to enclose an interconnection between the inner conductor and the inner contact. Sealant may be applied to the interconnection to improve seal performance and the dimensions and materials of the interconnection cap may be adjusted to modify characteristic impedance for return loss optimization with respect to specific coaxial cables.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/184,573 “Coaxial Connector for Solid Outer Conductor Coaxial Cable” filed Jun. 5, 2009 by Nahid Islam and Al Cox, currently pending and hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to electrical connectors for coaxial cable. More particularly the invention relates to a coaxial cable interconnection cap that provides an exchangeable tuning element and/or environmental seal for at least the inner conductor to inner contact electrical interconnection. 
     2. Description of Related Art 
     Prior coaxial connectors typically rely upon multiple seals between the connector, coaxial cable and/or interface element joints to prevent entry of moisture and/or humid air into the coaxial connector. The plurality of environmental seals significantly increases the complexity of the coaxial connector manufacture as well as assembly and installation procedures. 
     Coaxial connectors may be tuned for impedance matching with the intended coaxial cable and/or operating frequency to improve electrical performance. However, tuning a coaxial connector for each likely coaxial cable and/or operating frequency may require manufacture and inventory of a large number of different coaxial connector designs. An alternative method of impedance matching a connector with a specific coaxial cable is to apply an additional cable specific coring tool to selectively remove foam dielectric from the coaxial cable end. Such coring tools are costly and not always precise in the amount of dielectric removed/impedance matching achieved. 
     Dielectric elements have been applied within coaxial connectors as supporting insulators for the inner contact and/or proximate the interconnection between the inner conductor and an inner contact, to align the inner contact concentric with the outer conductor, create/enhance an inward bias upon the inner conductor by the inner contact and/or to support ramp structures for guiding and/or flaring the outer conductor during connector to cable attachment. 
     Competition within the coaxial cable and connector industry has focused attention upon improving electrical performance as well as reducing manufacturing, materials and installation costs. 
     Therefore, it is an object of the invention to provide a method and apparatus that overcomes deficiencies in such 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 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 isometric 90 degree cut-away view of a first exemplary interconnection cap. 
         FIG. 2  is a schematic isometric 90 degree cut-away view of  FIG. 1 , including an inner contact. 
         FIG. 3  is a schematic isometric 90 degree cut-away side view of a coaxial connector assembly with the interconnection cap of  FIG. 1 , with a coaxial cable attached. 
         FIG. 4  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 5  is a schematic cut-away side view  FIG. 4 . 
         FIG. 6  is a schematic isometric 90 degree cut-away side view of a coaxial connector assembly with the interconnection cap of  FIG. 4 , with a coaxial cable attached. 
         FIG. 7  is a close-up view of  FIG. 6 . 
         FIG. 8  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 9  is a schematic cut-away side view  FIG. 8 . 
         FIG. 10  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 11  is a schematic cut-away side view  FIG. 10 . 
         FIG. 12  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 13  is a schematic cut-away side view  FIG. 12 . 
         FIG. 14  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 15  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 16  is a schematic isometric 90 degree cut-away side view of a coaxial connector assembly with the interconnection cap of  FIG. 15 , with a coaxial cable attached. 
         FIG. 17  is a close-up view of  FIG. 16 . 
         FIG. 18  is a schematic isometric view of another embodiment of an interconnection cap. 
         FIG. 19  is a schematic isometric view of another embodiment of an interconnection cap. 
     
    
    
     DETAILED DESCRIPTION 
     Prior coaxial cables typically have inner and outer conductors made from copper and copper alloy. The inventor has recognized that new coaxial cable configurations and/or materials such as inner and/or outer conductors of aluminum and/or aluminum with copper or other metallic outer coating may require improved protection of the electrical interconnection, especially when these materials are connected to the dissimilar metals commonly applied to electrical connectors. Further, prior coaxial connector designs originally prepared for specific prior copper conductor coaxial cables may require significant impedance matching redesign prior to use with these new coaxial cable configurations. 
     The environmental seals in prior coaxial connectors are typically located around entry paths through the connector body and therefore do not protect the electrical interconnection between the inner conductor and the inner contact from any moisture which (a) may migrate past environmental seals of the connector body, (b) is sealed within the connector during installation and/or (c) may migrate to the electrical interconnection area along the inside of the coaxial cable. 
     An installation error and/or failure of any one of these connector body environmental seals may allow moisture and/or humid air to enter the connection areas of the connector where it can pool and cause corrosion, oxidation, increased contact resistance and/or IMD resulting in significant performance degradation of the electrical connections. 
     In the case of metals such as aluminum, an oxide film is formed on surfaces exposed to atmosphere in a very short time (within seconds). Also, accelerated galvanic corrosion can occur between aluminum and other metals in presence of an electrolytic solution, such as water. 
     In a coaxial connector incorporating an interconnection cap according to the invention, local isolation of the interconnection area is provided, reducing the overall seal area required and improving the reliability of the environmental seal. Further, modifications to the materials and/or dimensions of the interconnection cap may be cost effectively applied to enhance an impedance match of the coaxial connector with a specific coaxial cable, such as smooth wall or corrugated outer conductor coaxial cable, without requiring extensive modifications to the remainder of the associated coaxial connector. 
     A first embodiment of an interconnection cap  1 , as shown in  FIGS. 1-3 , also supports the inner contact  3  within a coaxial cable connector assembly  5  replacing the traditional inner contact supporting insulator. The interconnection cap  1  may be formed as a unitary monolithic body  7 , for example by injection molding, with a connector end  9  and a cable end  11  provided with a mounting portion  13  proximate the connector end  9 . The outer diameter of the mounting portion  13  may be dimensioned to seat the interconnection cap  1  within a connector body  15  of the coaxial cable connector assembly  5 . 
     One skilled in the art will appreciate that connector end  9  and cable end  11  are applied herein as identifiers for respective ends of both the overall coaxial connector assembly  5  and also of discrete elements of the assembly described herein, to identify same and their respective interconnecting surfaces according to their alignment along a longitudinal axis of the coaxial connector assembly  5  between a connector end  9  and a cable end  11 . 
     A bore  17  through the dielectric body  7  is dimensioned to seat the inner contact  3  therein, retaining the inner contact  3  coaxial with the connector body  15 . The bore  17  may be formed with an inner diameter that increases between the connector end  9  and the cable end  11 , for example via a step  19  against which an increased diameter contact portion  21  of the inner contact  3  abuts, preventing further movement of the inner contact  3  towards the connector end  9 . The contact portion  21  receives and engages the inner conductor  27  in an electro-mechanical interconnection, for example via a spring basket or other plurality of inward biased spring fingers. 
     An annular first seal groove  23  may be provided in an inner diameter of the bore  17  proximate the cable end  11 . An inner conductor seal  25  may be seated in the first seal groove  23 , for example an o-ring or other form of annular gasket. To improve the seal characteristics of inner conductor seal  25  and/or minimize the chance for misplacing and/or unseating the inner conductor seal  25  during assembly and/or cable to connector installation, the inner conductor seal  25  may be over-molded upon the dielectric body  7 . The inner conductor seal  25  is dimensioned to seal between the interconnection cap  1  and the inner conductor  27  as the inner conductor  27  is inserted to couple with the contact portion  21  of the inner contact  3 . 
     Similar to the sealing of the electrical connection between the inner conductor  27  and the inner contact  3 , the interconnection cap  1  may also be configured to provide an alignment surface for and/or seal against the inner diameter of the outer conductor  29 , aligning the inner contact  3  concentric with the outer conductor  27 . Thereby, as the coaxial cable is manipulated with respect to the coaxial connector after interconnection the concentric alignment of the inner contact  3  and outer conductor  27  is maintained, reducing the tendency for such misalignments and/or shifts of increased magnitude along contact surfaces to generate IMD. 
     For example, an outer diameter aligning portion  31  of the dielectric body  7  proximate the cable end  11  may be provided with an annular second seal groove  33  around the outer diameter. The second seal groove  33  receives an outer conductor seal  35  dimensioned to seal between the interconnection cap  1  and an inner diameter of the outer conductor  29  when the outer conductor  29  is coupled to the connector body  15 . The outer conductor seal  35  may also be an o-ring or other form of annular gasket and/or may be over-molded directly upon the second seal groove  33 . 
     To reduce material costs and overall connector assembly weight, a material reduction groove  37  may be located between the mounting portion  13  and the aligning portion  31 . Depending upon the dimensions of the coaxial cable  39  and the selected connection interface for the coaxial cable connector assembly, the diameter of the mounting portion  13  may be smaller than the diameter of the aligning portion  31 . To locate the outer conductor seal  35  at a position for contacting the inner diameter of the outer conductor  29 , the interconnection cap  1  may extend beyond the connector body  15  at the cable end  11 . Further, the aligning portion may be provided with step and/or ramp surfaces to align the outer conductor seal  35  with the outer conductor  29 , for example where the outer conductor inner diameter is the same as the inner diameter of a body bore of the connector body  15  at the cable end  11 . 
     In addition to a seal design to prevent aluminum oxidation and/or corrosion, an interconnection cap  1  according to the invention may also include a surface sealant  41  (notation  41  in the various figures indicates several possible general surface sealant  41  application area(s), as the surface sealant  41  may be applied in coating thicknesses that are too thin to graphically represent in the various figures) such as an oxidation and/or corrosion inhibitor coating or grease. An example of suitable surface sealant(s) is the family of Dostex™ oxide inhibitors available from Dossert Corporation of Waterbury, Conn., US. 
     The surface sealant  41  may be applied to the inner conductor seal  25 , outer conductor seal  29 , first seal groove  23 , second seal groove  33 , inner contact  3 , the cable end  11  of the bore  17  and/or the inner conductor  27 . A filling of the interconnection area to the exclusion of air upon interconnection is preferred, short of spilling out of the interconnection area. 
     Where the surface sealant  41  is applied, for example to the inner conductor seal  25  and/or first seal groove  23 , displacement of the inner conductor seal  25  into/against the first seal groove  23  as the inner conductor  27  is moved towards the inner contact  3  will spread a coating of the surface sealant  41  upon the inner conductor  27 . When the inner contact  3  couples with the surface sealant  41  coated inner conductor  27 , the mechanical force of the inner contact  3  will displace the surface sealant  41  from the immediate area of the electrical interconnection, sealing the electrical interconnection from exposure to the atmosphere and any moisture that may be present. 
     Alternatively, the surface sealant may be applied to exposed surfaces of the electrical interconnection area, coaxial cable connector assembly  5  and/or coaxial cable  39  as a manual step of a method for coupling the coaxial cable connector assembly  5  to the end of the coaxial cable  39 . 
     One skilled in the art will appreciate that the present invention may be easily integrated with existing coaxial connector configurations with a minimum of engineering rework and/or tooling modification. The required modifications may be limited to the exchange of a conventional insulator configuration with an interconnection cap  1  according to the invention. 
     In another embodiment demonstrated in  FIGS. 4-7 , the several benefits of the invention may be realized without modifying the traditional inner contact supporting insulator  43 . As shown in  FIG. 3 , the interconnection cap  1  may be formed as a generally cylindrical body dimensioned to seat upon an outer diameter of the contact portion  21  of the inner contact  3  projecting from the cable end  11  of the insulator  43  and sealing against the outer diameter of the inner conductor  27 , for example via an inner conductor shoulder  47 . 
     The covering of the contact portion  21  is defined as a covering which forms a surrounding enclosure of the inner contact and inner conductor interconnection, sealing against the inner conductor  27  and against the inner contact  3  at a location which seals the contact portion  21 . For example, the contact portion  21  is covered such that any slots or the like between spring fingers forming the spring basket are covered, fully surrounding and sealing the interconnection. 
     As shown for example in  FIGS. 8 and 9 , the bore  17  may be provided with a taper between a minimum diameter proximate a cable end  11  of the interconnection cap  1  and a maximum diameter proximate a connector end  9  of the interconnection cap  1 . Thereby, the bore  17  follows a steady state contour of the contact portion  21 , for example the inward direction of the spring basket prior to insertion of the inner conductor  27 . To minimize slippage while seated along the taper of the contact portion  21 , the interconnection cap  1  may be provided with an inward projecting connector end shoulder  49  dimensioned to engage a groove and/or shoulder feature of the inner contact  3  in a snap fit. When the inner contact  27  contacts and radially spreads the spring basket during insertion, an elastic property of the material selected for the interconnection cap  1 , such as an elastomeric material with a high durometer, may provide additional strength to the contact portion  21 , enabling the inner contact  3  to be formed from a less expensive material such as brass, instead of the phosphor bronze typically utilized for its spring characteristic. 
     A stripping feature  51  may be applied to the interconnection cap  1  to provide a scraping action upon the inner conductor outer diameter immediately prior to entry into the interconnection area as a last cleaning of any surface contamination such as residue from dielectric of the coaxial cable  39  that might otherwise foul the interconnection. Alternatively, the scraping feature may be provided with sufficient grip and/or strength to scrape off any surface oxidation that may be present on the inner conductor surface. 
     For example as shown in  FIGS. 10 and 11 , the stripping feature  51  may be formed as a plurality of stripping finger(s)  53  provided arrayed around the cable end of the interconnection cap, projecting radially inward. 
     For example as shown in  FIGS. 12 and 13 , the stripping feature  51  may be formed as a scrape surface  55  provided on an inner diameter of the inner conductor shoulder  47 . The scrape surface  55  may be formed, for example, as a plurality of longitudinal or annular grooves. 
     The material selected for the interconnection cap  1  may impact the sealing characteristics. For example, where a material with an elastic characteristic is applied, the material may be relied upon to seal against the inner conductor  27  and contact portion  21  without additional seal features, for example as shown in  FIGS. 10 and 11 . Alternatively, where a relatively inelastic material is applied, for example where the interconnection cap  1  requires rigidity for supporting the inner contact  3  as in  FIGS. 1-3  and/or a metal material is used to obtain a scrape surface  55  as in  FIGS. 12 and 13 , the first seal groove  23  and a third seal groove  45 , provided in the bore  17  proximate the connector end, may be applied as seats for gaskets such as the inner conductor seal  25  and/or for filing with surface sealant  41 . 
     The interconnection cap  1  may be applied in embodiments similar to the first embodiment described in detail with respect to  FIGS. 1-3 , but where the inner contact  3  remains supported by a conventional separate insulator  43  and the interconnection cap  1  provides only sealing and/or characteristic impedance tuning for return loss optimization/coaxial cable matching. The outer diameter aligning portion  31  may be provided in an outer conductor aligning/flaring configuration, for example as shown in  FIG. 14 , or an outer conductor aligning/sealing configuration, for example as shown in  FIGS. 15-17 . 
     The configuration of the interconnection cap  1  impacts an impedance match between the overall coaxial connector assembly  5  and the coaxial cable  39 . By varying the dimensions and/or selecting interconnection cap materials with different dielectric constants, the interconnection cap  1  may also or alternatively be utilized as a coaxial connector assembly characteristic impedance tuning element. One skilled in the art will appreciate that material selection and/or modification of the interconnection cap radial dimensions, including the addition, for example, of an outward projecting impedance matching shoulder  57  as shown for example in  FIG. 18  and/or addition of aperture(s)  59  applied to the aligning portion  31 , as shown for example in  FIG. 19 , enables characteristic impedance tuning of the interconnection cap  1  and therethrough of the coaxial connector assembly  5  without requiring redesign of existing coaxial connector configurations. 
     By providing a range of differently configured interconnection cap  1 , a single coaxial connector assembly  5  may be field configured for high performance with specific coaxial cables, simply by exchanging the interconnection cap  1  prior to connector to cable installation. 
     An interconnection cap  1  according to the invention may provide an improved environmental seal located proximate the electrical interconnection connection between the inner conductor  27  and the inner contact  3 , thus reducing opportunities for connector failure due to corrosion and/or oxidation inherent in metals such as aluminum alloys and/or when these metals are mechanically coupled to dissimilar metals. The interconnection cap  1  according to the invention is especially suited for use in electrical connectors for a coaxial cable  39  with an aluminum inner conductor  11  having a copper or other metal coating about the outer diameter surface. Because the exposed end of the inner conductor  27  and the metal coating edge exposed by cable end preparation for coaxial cable connector assembly  5  attachment is protected from moisture and/or air exposure, opportunities for accelerated corrosion of the exposed aluminum and/or related delamination of the metal coating are reduced, especially when a surface sealant  41  is applied to the cavity formed by the inner contact  3  and the bore  17  prior to insertion of the inner conductor  27 , to further exclude air and/or moisture from the area of the electrical interconnection. Similarly, the interconnection cap  1  may be configured to provide a seal against the inner diameter of the outer conductor  29  further isolating the coaxial cable connector assembly  5  from any moisture that may be present in or migrating along the inside of the coaxial cable  39 . 
     Although exemplary combinations of the coaxial cable connector assembly  5  and coaxial cable  39  are provided demonstrating outer conductor threaded clamp retention configurations for smooth coaxial cable(s)  39 , one skilled in the art will recognize that the interconnection cap  1  is applicable to any desired combination of the coaxial cable connector assembly  5  and coaxial cable  39 , including corrugated conductor cable configurations. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 Table of Parts 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 interconnection cap 
               
               
                 3 
                 inner contact 
               
               
                 5 
                 coaxial cable connector assembly 
               
               
                 7 
                 dielectric body 
               
               
                 9 
                 connector end 
               
               
                 11 
                 cable end 
               
               
                 13 
                 mounting portion 
               
               
                 15 
                 connector body 
               
               
                 17 
                 bore 
               
               
                 19 
                 step 
               
               
                 21 
                 contact portion 
               
               
                 23 
                 first seal groove 
               
               
                 25 
                 inner conductor seal 
               
               
                 27 
                 inner conductor 
               
               
                 29 
                 outer conductor 
               
               
                 31 
                 aligning portion 
               
               
                 33 
                 second seal groove 
               
               
                 35 
                 outer conductor seal 
               
               
                 37 
                 material reduction groove 
               
               
                 39 
                 coaxial cable 
               
               
                 41 
                 surface sealant 
               
               
                 43 
                 insulator 
               
               
                 45 
                 third seal groove 
               
               
                 47 
                 inner conductor shoulder 
               
               
                 49 
                 connector end shoulder 
               
               
                 51 
                 stripping feature 
               
               
                 53 
                 stripping finger 
               
               
                 55 
                 scrape surface 
               
               
                 57 
                 impedance matching shoulder 
               
               
                 59 
                 aperture 
               
               
                   
               
             
          
         
       
     
     Where in the foregoing description reference has been made to 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.