Patent Publication Number: US-6666725-B2

Title: Broadband coaxial microwave connector

Description:
BACKGROUND 
     The present invention concerns microcircuit housing and cable connectors and pertains particularly to a broadband coaxial microwave connector. 
     For telecommunications applications with signal frequencies below 2 gigahertz, a variety of connectors for coaxial cable systems are used. For example, the most common type of connector is an F-connector that includes a male F-connector part and a female F-connector part. A male F-connector is typically used to terminate a coaxial cable. A female F-connector may be used to join two cables together or to connect a cable to a device. 
     Other coaxial cable connectors include use of an electrical socket that include cantilever spring tines which terminate in a convex cross section at their free ends. The spring tines expand as they guide an inserted pin during engagement. Another coaxial cable connector uses a circular sleeve having a plurality of spaced-apart, axially oriented tines. Another coaxial cable connector uses spring tabs. For a general discussion on low cost coaxial cable connectors, see for example, U.S. Pat. No. 5,865,654. 
     For microwave applications, conventional coaxial connectors can include an inner conductor, an outer conductor and an inwardly threaded nut. The inwardly threaded nut is designed to engage an outwardly threaded mating connector. Front faces of respective inner conductors and outer conductors contact each other at a reference plane once the nut is threaded onto the receiving outer conductor. To permit machining of the conductors, a moderately soft conductor material, such as beryllium-copper alloy, is used. To maximize performance, the inner and outer conductors can be gold plated. The gold provides optimal conductivity and resistance to oxidation and other forms of corrosion. 
     In one microwave coaxial connector, an outer conductor and a coupling nut are configured to incorporate ball bearings therebetween to minimize frictional engagement as the nut is tightened down on a receiving connector. The ball bearings are placed between an outer surface of the outer conductor and an inner surface of the nut. The ball bearings minimize friction between the nut and the outer conductor to which it is coupled. As a result, relative rotation of mating faces is minimized as the nut is tightened. Thus, damage to mating faces is minimized. As an additional advantage, torque-induced stress on cables and devices mechanically coupled to the connectors is minimized. See, for example U.S. Pat. No. 4,801,274. 
     To achieve a wiping contact on the center conductors, previous connector designs use a pin and slotted socket design. Alternatively, in sexless connectors, compressible collets are imbedded in the ends of the butting center conductors. While this works acceptably for coaxial connectors having a center conductor diameter of about 0.43 millimeter (mm), such connection of center conductors is not practical for a DC to 200 gigahertz (GHz) connector where the center conductor of a transmission line portion has a diameter of about 0.254 mm. 
     There are connection techniques that can be used for implementing connection of transmission lines where the center conductor of a transmission line has a diameter of about 0.254 mm. These include ribbon bonding or overlapping transmission line connections. However this style of connection is impractical for applications where there are repeated connects and disconnects. Nevertheless, it is desirable to have such a broadband coaxial connector for DC to 200 GHz that can be installed on a test instrument or a microcircuit to be used inside an instrument or a product. 
     SUMMARY OF THE INVENTION 
     In accordance with the preferred embodiment of the present invention, a connector assembly includes a first connector half and a second. The first connector half includes a first transmission line that has a first outer conductor and a first center conductor. The first center conductor has a first end that has an angled flat region. The second connector half includes a second transmission line. The second transmission line includes a second outer conductor and a second center conductor. The second center conductor has a first end that has an angled flat region. When the first connector half and the second connector half are connected together, the first outer conductor is electrically connected to the second outer conductor. A wiping contact is established between the angled flat region of the first end of the first center conductor and the angled flat region of the first end of the second center conductor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a back view of a keyed coupled mating system in accordance with a preferred embodiment of the present invention. 
     FIG. 2 shows a front view of a keyed coupled mating system in accordance with a preferred embodiment of the present invention. 
     FIG. 3 shows additional detail of one connector half in accordance with a preferred embodiment of the present invention. 
     FIG. 4 is a cross-sectional view of connection of connector halves in accordance with a preferred embodiment of the present invention. 
     FIG. 5 shows additional detail of the connection of the connector halves shown in FIG. 4 in accordance with a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a back view of two identical connector halves that form a keyed coupled mating system. A first connector half  150  is shown in FIG. 1 to include a flange  100  and a coupling nut  101 . A transmission line connected to the first connector half  150  includes an outer conductor  102  and a center conductor  103 . For example, outer conductor  102  has a 0.60 mm (0.0236 inch) interior diameter to enable it to work mode free to 200 GHz. Center conductor  103  has a 0.254 mm (0.010 inch) outer diameter. This results in a 50 ohm transmission line. 
     A second connector half  250  is shown in FIG. 1 to include a flange  200  and a coupling nut  201 . A transmission line connected to the second connector half  250  includes an outer conductor  202  and a center conductor  203 . For example, outer conductor  202  has a 0.60 mm (0.0236 inch) interior diameter to enable it to work mode free to 200 GHz. Center conductor  203  has a 0.254 mm (0.010 Inch) outer diameter. This results in a 50 ohm transmission line. 
     FIG. 2 shows a front view of the two connector halves forming the keyed coupled mating system. When an outer threaded body  108  with a flat  104  of first connector half  150  and an outer threaded body  208  with a flat  204  of second connector half  250  are oriented the same, they can be mated. In the preferred embodiment, first connector half  150  and second connector half  250  can only be mated in this one orientation. A close up of an area  104  of FIG. 2 is shown in FIG.  3 . 
     FIG. 3 shows an example arrangement of cogs  106  on threaded body  108 . When the connector is fully mated, an angled flat region  107  of center conductor  103  forms a wiping contact with a corresponding angled flat region of center conductor  203 . Thus, threaded body  108  and threaded body  208  act as keyed coupling bodies. 
     FIG. 4 is a cross-sectional view of connector halves  150  and  250  coupled together. The procedure to perform the mating is performed as described immediately below. 
     Coupling nuts  101  and  201  are spun completely back to connector flanges  100  and  200 , respectively. This exposes the threads on outer threaded bodies  108  and  208 . Connector halves  150  and  250  to be mated should be in the same orientation. This can be verified by orienting flat  104  and flat  204  either both up or down. Connector halves  150  and  250  are then swiveled 90 degrees toward each other and brought together so that they are axially in line. When they are in the right orientation, the cogs on outer threaded bodies  108  and  208  fit together (only one way). Connector halves  150  and  250  are brought together so that outer conductors  102  and  202  touch. The angled flat regions  107  and  207  (shown in FIG. 5) on center conductors  103  and  203 , respectively, are thus in the right orientation and since they are slightly longer then the outer conductors  102  and  202 , respectively, angled flat regions  107  and  207  will slide on each other and make a wiping contact as the connection of connector halves  150  and  250  is tightened. 
     One of the two coupling nuts is spun toward the interface of connector halves  150  and  250 , first over the threads of its&#39; own outer threaded body, then threaded on to the outer threaded body on the opposing side. For example, in FIG. 4, coupling nut  101  is spun toward the interface of connector halves  150  and  250 , first over the threads of outer threaded body  108 , then threaded on to outer threaded body  208  while disengaging thread on outer threaded body  108 . By this action outer threaded body  208  is pulled toward outer threaded body  108 . A 5 Inch-Pound torque wrench is used to tighten the connection. The torque wrench for subminiature type A (SMA) connectors is recommended. 
     A coupling nut snap ring  209  is also shown in FIG. 4. A close up of an area  110  of FIG. 4 is shown in FIG.  5 . 
     FIG. 5 shows additional detail of the connection of connector halves  150  and  250  shown in FIG.  4 . In FIG. 5, a length  211  represents the inner diameter of outer conductor  202 . Nonconductive filling  206  provides support for center connector  203 . Angled flat regions  107  and  207  are shown providing a wiping contact at a location  112 . Coupled thread  222  is shown to reside on outer threaded body  208 . 
     The dimensions of the outer conductor inner diameter can be scaled further down in size, for example, to 0.5 mm (0.0197 Inch) or less to work up to 220 GHz and above. In this case the outer diameter of the center conductor also has to be correspondingly reduced. The subsequent smaller/higher frequency versions can be interconnected with this configuration with a relatively small additional reflection and no mechanical problems at the interface of the two transmission lines. 
     The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For example, an embodiment of a connector used for microcircuit housing is disclosed. The invention works equally well for connection of coaxial cables when a different detail is used on the ends of the connector halves away from the mating plane. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.