Abstract:
The present invention relates generally to an apparatus for interconnecting coaxial connectors with stripline circuits. A general coaxial connector housing is by glue fixed adjacent to the stripline circuit and at least one conductive element is placed in between the connector housing and the stripline ground planes.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention generally concerns a connector for connecting transmissions paths. Specifically, the present invention relates to an apparatus for interconnecting coaxial connectors with stripline circuits. 
     DESCRIPTION OF RELATED ART 
     It is well known that special precautions must be taken when dealing with signal transmission circuits in the radio to microwave frequency range. Otherwise unwanted transmission losses, reflections and other undesirable characteristics can result. Microwave signals are often carried on shielded coaxial cables. These cables are typically used to transmit microwave signals to and from various end devices. Many of these end devices require that connections to them are made by way of flat or “stripline” conductors residing on a surface of a dielectric board (hereinafter “a stripline circuit”). Examples of such devices include power splitters, mixers, hybrid couplers, directional couplers, filters, attenuators, phase shifters, antenna elements and antenna arrays. 
     In e.g. U.S. Pat. No. 5,618,205 a transition between a stripline circuit and coaxial conductor approaching the circuit perpendicularly is shown as the right angle connector. 
     In e.g. U.S. Pat. No. 5,550,521 a coaxial connector socket is fixed to an outside wall of an electromagnetic shielded box, where inside the box an electronic circuit is implemented on a substrate. An electrically conductive ring is provided in such a way so the socket is in contact with the grounding surface of the socket and the bottom plate of the box simultaneously as the conductor core is insulated from the socket and bottom plate. 
     Further in e.g. U.S. Pat. No. 4,867,704 a coaxial connector is fixed to a stripline circuit by a fixture, a pair of metallic blocks providing an electrically and mechanically satisfactory connector. 
     SUMMARY OF THE INVENTION 
     The problem dealt with by the present invention is to provide electrical connections between the housing of a coaxial connector and the ground planes of a stripline circuit, particularly at microwave frequencies where relatively minor misalignment may cause serious electric field distortion. Other problems include facilitating mounting of a coaxial cable connector to a flexible stripline circuit, and improving mechanically the connection between the coaxial connector and the stripline circuit. 
     Briefly, the present invention solves said problem when using a general coaxial connector by gluing the connector housing so as to be terminated adjacent to the stripline circuit using a conductive element in between the connector housing and the stripline ground planes. 
     Specifically, the problem is solved by the coaxial connector according to claims  1  and  7 . 
     An object of the invention is to provide, between a stripline circuit and a coaxial conductor, a connection that has a relatively low VSWR (voltage standing wave ratio) over a wide range of frequencies, especially at microwave frequencies. 
     Another object is to provide good mechanical connection between the coaxial connector and the stripline circuit. 
     A further object is to provide proper alignment of the coaxial connector and the conductive elements to which existing stripline circuit can be readily adapted, and which is simple and economical to manufacture. 
     An advantage of the present invention is that a connection that has a relatively low VSWR (voltage standing wave ratio) over a wide range of frequencies, especially at microwave frequencies, between a stripline circuit and a coaxial conductor can be obtained. 
     Another advantage is that a good mechanical connection between the coaxial connector and the stripline circuit can be attained. 
     Still another advantage of the present invention is that proper alignment can be obtained of the coaxial connector and the conductive elements to which existing stripline circuit can be readily adapted, and which is simple and economical to manufacture. 
     Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial view of a coaxial connector assembly embodying the principles of one embodiment of the invention and depicted with a fragmentarily represented stripline circuit. 
     FIG. 1 a  is an enlarged part of FIG. 1 illustrating the conductor tab. 
     FIG. 1 b  is an enlarged part of FIG. 1 illustrating one conductive element. 
     FIG. 1 c  is an enlarged part of FIG. 1 illustrating the stripline circuit. 
     FIG. 2 a  is a projected part B—B of FIG. 1, illustrating the end part of the connector housing, the adhesive substance, and a part of the stiffening layers corresponding to FIG. 3 a.    
     FIG. 2 b  is a projected part B—B of FIG. 1, illustrating the end part of the connector housing, the adhesive substance, and a part of the stiffening layers corresponding to FIG. 3 d.    
     FIG. 2 c  is a projected part A—A of FIG. 1, illustrating the conductive elements and a part of the stiffening layers corresponding to FIGS. 3 a-d  and FIG.  5 . 
     FIG. 3 a  is a perspective view of a part of FIG. 1, illustrating the stripline circuit and a first embodiment of the stiffening layers. 
     FIG. 3 b  is a perspective view of a part of FIG. 5, illustrating the stripline circuit and a second embodiment of the stiffening layers. 
     FIG. 3 c  is a perspective view of a part of FIG. 1, illustrating the stripline circuit and a third embodiment of the stiffening layers. 
     FIG. 3 d  is a perspective view of a part of FIG. 1, illustrating the stripline circuit and a fourth embodiment of the stiffening layers. 
     FIG. 4 a  is a projected part C—C of FIG.  1  and FIG. 5, illustrating an exemplary general connector housing with a rectangular end part, a part of the stiffening layers and adhesive substance. 
     FIG. 4 b  is a projected part C—C of FIG.  1  and FIG. 5, illustrating an exemplary general connector housing with a round end part, a part of the stiffening layers and adhesive substance. 
     FIG. 5 is an axial view of a coaxial connector assembly embodying the principles of a second embodiment of the invention and depicted with a fragmentarily represented stripline circuit. 
     FIG. 5 a  is a projected part D—D of FIG. 5, illustrating the stripline circuit, the end part of the connector housing, and a fifth embodiment of the stiffening layers. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to the drawings, a coaxial cable connector is illustrated as coupling high frequency signals between a coaxial connector and an end device. It should be understood from the outset that the coaxial connector is shown in its most simple form, i.e., with one end device and one coaxial connector. However, it should be understood that the teachings of this invention are applicable to a future end device, which would accommodate a much larger number of connections. In addition, the specifically disclosed male/female positions can be reversed if desired. 
     Coaxial cable includes a conventional male end connector, which includes a shielded male pin extending therefrom. The male coaxial connector mates with a conventional female connector that is attached to a stripline circuit. As perhaps shown best in FIG. 1 a housing  110  of a female coaxial connector including one end part  117  with a planar end wall and opposite a protruding part  116  that mates with the male coaxial connector. The housing  110  includes a conductive center pin  111  having a recess  113  in its protruding part  116  receiving the male pin of the male connector. The opposite end of pin  111  terminates in a recess  114  to receive a tab  134 , a continuation of a center conductive layer  131  from the stripline circuit  130 . As will be recognized by those skilled in the art, the tab  134  could also be protruding out of the coaxial connector housing  110 , meeting a recess into the center conductive layer  131 . Some kind of dielectric material  112  surround the concuctive center pin  111 , it prevents the conductive center pin  111  from being in contact with the housing  110 , that can in turn be conected to ground. Threads  115  can be included on the housing  110  of the female coaxial connector, on its outer end, the threads  115  can engage inner threads on the male connector. 
     The conductive tab  134 , in FIG. 1 a , extending from the stripline circuit  130  is connected to the recess  114  in the end part  117  of the connector housing  110 , and the end part  117  is terminated adjacent to the stripline circuit  130 ; in the same plane  135 , longitudinally with the stripline circuit  130 . The stripline circuit  130  in FIG. 1 has a first ground plane  133   a , a first dielectric layer  132   a , a center conductive layer  131  including two layers  131 ,  121  see FIG. 1 c , a second dielectric layer  132   b , and a second ground plane  133   b . Normally the stripline circuit  130  in FIG. 1 c  is obtained from two dielectrics layers  132   a-b  made of e.g. microwave laminate. On each side of one of the dielectric layer  132   a  a conductive plane  133   a ,  131  of e.g. copper is attached. One of the conductive planes (e.g.  131 ) is etched to form the conductive pattern, and the conductive plane opposite become the ground plane  133   a . The second dielectric layer  132   b  with one conductive plane  133   b  is glued together with the part opposite the ground plane  133   b , with e.g. a bond film  121  to the etched conductive plane  131 . The conductive plane  133   b  of the second dielectric layer  132   b  is now the second ground plane  133   b , and the etched conductive plane  131  is forming the center conductive layer  131 . Before gluing the two dielectric layers  132   a-b  together, a pin  134  is soldered at the etched plane  131 , which is flat in one end and round in the opposite end. The pin  134  is soldered in such a way so the flat part is in contact with the etched plane  131  and the round part sticks out from the stripline circuit  130 . When the dielectric layers  132   a-b  are glued together with the bond film  121 , the etched conductive layer  131  with the side of the second dielectric layer  132   b  which is opposite of the second conductive plane  133   b , the pin  135  become the protruding tab  134 . As will be recognized by those skilled in the art, the center conductive layer  131  together with the tab  134  may be obtained in another way than described above e.g. made in one solid layer, and the protruding tab  134 , may be a continuation of the solid layer  131 . 
     The first and second dielectric layers  132   a-b  are made of e.g. a microwave laminate, RO3003, with a certain dielectric constant to perform isolation between the center conductive layer  131  and the first and second ground planes  133   a-b . The stripline circuit  130  including the ground planes  133   a-b  and dielectric layers  132   a-b  and center conductive layer  131  can be made of soft material so that it is necessary to put one stiffening layer  141   a  to the first ground plane  133   a , and another second stiffening layer  141   b  to the second ground plane  133   b . The stiffening layers  141   a-b  are e.g. made of FR4 laminate, which stiffens the soft stripline circuit  130  enough to avoid it from breaking. But it can be of any material that stiffens the stripline circuit such as e.g. plastic or metallic. The stiffening layers  141   a-b  are e.g. with NO-FLO PREPREG glued together with the ground planes  133   a-b.    
     A first stiffening layer  141   a  is attached to the first ground plane  133   a , a cavity  142   a ,  143   a ;  142   a ,  145   a  is formed in the first stiffening layer  141   a  so a first conductive element  150   a  can be provided in the cavity  142   a ,  143   a ;  142   a ,  145   a  see different form of cavities  142   a ,  143   a ;  142   a ,  145   a ;  142   b ,  143   b ;  142   b ,  145   b  in the stiffening layers  141   a-b.    
     The connector housing  110  include one end part  117  with a planar end wall that terminates in alignment with the stripline circuit  130 . The form of the end part  117  of the connector housing  110  can e.g. be rectangular as seen in FIG. 4 a  together with FIG. 1 or  5 , or e.g. round as can be seen in FIG. 4 b  together with FIG. 1 or FIG.  5 . The rectangular end part  117  in FIG. 1 or  5  together with FIG. 4 a  has four sides  119   a-d  (corresponding to  519   a-d  in FIG. 5, where only  519   a-b  is shown) and the round end part  117  in FIG. 1 or FIG. 5 together with FIG. 4 b  has one round side  118 . Mechanically the connector housing  110 , e.g. of a SMA type connector with serial number R12546001 from Radiall, is glued e.g. with a non-conductive adhesive substance  120  onto the stiffening layers  141   a-b . An example of a non-conductive glue that becomes solid when it gets dried is MVK89 with serial number AV138/998 from CIBA. But any adhesive substances  120  may be used that have these characteristics. 
     If the first stiffening layer  141   a  and second stiffening layer  141   b  are elongated so as to protrude above the stripline circuit  130 ,  135  as can be seen in FIGS. 3 a-d , the protruded parts  145   a-b  can support the connector housing  110 . In the first embodiment in FIG. 3 a  a terrace  144   a-b  is formed in between the remaining protruded parts  145   a-b  of the first and second stiffening layers  141   a-b , and the cavity  142   a ,  143   a ;  142   b ,  143   b . The end part  117  of the connector housing  110  may then get extra support from the terraces  144   a-b  in the case where the surface of the end part  117  has a size allowing it to be in contact with the terraces  144   a-b . In the projected view of FIG. 1, FIG. 2 a  B—B, the connector housing  110  is in contact with the terraces  144   a-b  as can be seen as the elongated side  119   a-b  that form a rectangular end part  117  over the edge  143   a ,  143   b  of the cavities  142   a ,  143   a ;  142   b ,  143   b . In the second embodiment in FIG. 3 b  the form of the stiffening layers  145   a-b  result in that the end part  117  of the connector housing  110  has support by the stripline circuit  130 ,  135 , but no support by any terraces. This second embodiment in FIG. 3 b  correspond to FIG. 5 where the stiffening layers  141   a-b ,  541   a-b  have attached extra layers  146   a-b ,  546   a-b . The end part  117 ,  517  must have a surface big enough so the conductive elements  150   a-b ,  550   a-b  is in contact with the end part  117 ,  517 . In the third embodiment in FIG. 3 c  similar to FIG. 3 b , where the difference is that beside the cavity  142   a ,  145   a ;  142   b ,  145   b  formed in between the first ground plane  133   a  and the first stiffening layer  132   a  and second ground plane  133   b  and the second stiffening layer  132   b , an extra bulge  147   a ,  147   b  is formed in the first and second stiffening layer  141   a-b . The end part  117  of the connector housing  110  has its support from the stripline circuit  130  and the bulge formed terraces  144   a-b . A connector housing  110  with a round formed end part  117  as can be seen in FIG. 4 b  is necessary. For the bulge form  147   a ,  147   b  side to be of any support for the connector housing  110 , the side  118  of the connector housing  110  should fit into the bulge  147   a ,  147   b  or leave a small space in between, see the adhesive substance  120  in the circle in FIG. 2 b  B—B. Actually the projected view in FIG. 2 b  B—B shows the embodiment in FIG. 3 d  where the stiffening layers  141   a-b  are adjacent to the ground planes  133   a-b  and the cavities  142   a ,  143   a ;  142   b ,  143   b  are more or less hidden. The end part  117  fit into the bulge part  147   a ,  147   b  in FIG. 3 d , and the bulge formed terraces  147   a ,  147   b  support the end part  117  as in FIG. 3 c . As will be recognized by those skilled in the art, e.g. drilling, or cutting can be used in making the cavities  142   a ,  143   a ;  142   b ,  143   b  and protruding parts  145   a ,  147   a ;  145   b ,  147   b  or the formation in the stiffening layers  141   a-b  can be made in the assembly of the stripline circuit  130 . 
     Returning to the conductive elements  150   a-b  shown respectively in a slit  142   a ,  143   a ;  142   b ,  143   b  in FIG. 1 or as shown in FIG. 5 the conductive elements  550   a ,  550   b  are placed in a recess  542   a ,  542   b  of the stiffening layers  541   a ,  541   b . In FIG. 1 is illustrated together with the projected view A—A in FIG. 2 c  that the conductive elements  150   a ,  150   b ,  550   a ,  550   b  are shaped in a tubular form. If they are made of a swamplike flexible material (e.g. elastomer shielding gasket) and are slightly bigger than the recesses  542   a ,  542   b  in FIG. 5 or the slits  142   a ,  143   a ;  142   b ,  143   b  in FIG. 1, they will be a bit deformed assuring good electrical performances between the end part  117 ,  517  of the connector housing  110 ,  510  and the ground planes  133   a-b ,  533   a-b . In FIG. 5 the conductive element  550   a  can protrude out a bit from the recess  542   a  when no extra layer  546   a  is fixed next to the side of the first stiffening layer  541   a . A mechanical improvement is obtained with the extra layers  546   a-b  as illustrated in FIG. 5 fixed adjacently towards the side of the first and second stiffening layers  541   a-b  compared to an embodiment without them. 
     As will be recognized by those skilled in the art the recess  542   a ,  542   b  in FIG. 5 or cavity  142   a ,  143   a ;  142   b ,  143   b  in FIG. 1 together with FIGS. 3 a-d  may have any shape, to provide the conductive elements  150   a-b ,  550   a-b  that may have any shape as well, the only limit is that a good transition must be made available for the end part  117 ,  517  of the connector housing  110 ,  510  and the ground planes  133   a-b ,  533   a-b . Dependant on the type of connector housing  110 ,  510  used in the embodiment, the form of the protruded part  145   a-b ,  545   a-b  of the stiffening layer  141   a-b ,  541   a-b  must be adjusted accordingly. For example a bulge form  147   a ,  147   b  illustrated in FIGS. 3 c-d  is not applicable if a rectangular shaped form of the end part  117  of the connector housing  110  is used, see FIG. 1 or  5  together with FIG. 4 a.    
     In FIG. 2 b  B—B a projected view shows the protruding parts  145   a-b  formed as a circular hole  147   a-b  with the adhesive substance  120  placed in between the side  118  of the end part  117  of the connector housing  110  and the circular protruding parts  145   a-b ,  147   a-b . In FIG. 2 a  B—B a projected view illustrates an elongated opening. The elongated opening of the protruded parts  145   a-b  is filled with the adhesive substance  120  between the protruded parts  145   a-b  and the side  118 ,  119   a-d  of the connector housing  110 . It is eligible that the adhesive substance  120  is applied between the edge  118 ,  119   a-d  of the connector housing  110  and the protruding parts  145   a-b  of the stiffening layers  141   a-b  and not smeared on the end part  117  of the connector housing  110 . In cases where at least one side  118 ,  119   a-d  of the end part  117  of the housing  110  is adjacent to the protruded stiffening layers  145   a-b ,  147   a-b  the adhesive substance  120  must be put where the adhesive substance  120  can be in contact with the connector housing  110  and the protruding sides  145   a-b ,  147   a-b , e.g. above the side  118 ,  119   a-d  of the connector housing  110 , between the neck part (the tapered part of the housing  110 ) of the housing  110  and the protruded stiffening layers  145   a-b ,  147   a-b . In this way the adhesive substance  120  will be functioning as an embedment for the connector housing  110  between the protruding parts  145   a-b  of the stiffening layers  141   a-b  at the same time as it is fixing the connector housing  110  to the stiffening layers  141   a-b . A preferred embodiment for the stiffening layers  141   a-b  are to include a terrace  144   a-b  in between the remaining protruding part  145   a-b  and the cavity  142   a ,  143   a ;  142   b ,  143   b  for best support of the end part  117  of the connector housing  110 , as in FIGS. 3 a ,  3   c-d.    
     A rigid connection between the connector housing  110  and the stripline circuit  130 , a good mechanical support, brings a good electrical connection, which is so important at microwave frequencies. If no remaining protruding parts  145   a-b ,  147   a-b  of the first and second stiffening layers  141   a-b  above the stripline circuit  130  surface  135  in FIG. 3 a  and no extra stiffening layers  546   a-b  are attached to the first and second stiffening layers  541   a-b  in FIG. 5, imply that the adhesive substance  120 ,  520  is smeared on the surface  135 ,  535  of the stripline circuit  130 ,  530  including the first and second ground planes  133   a-b ,  533   a-b  and first and second dielectric layers  132   a-b ,  532   a-b , this may cause non-conductive adhesive substance  120 ,  520  to be smeared on the conductive tab  134 ,  534  and on the side of the recess  142   a-b ,  542   a-b  of the ground planes  133   a-b ,  533   a-b . For this solution to work non-conductive adhesive substance  120 ,  520  may not be smeared on the conductive tab  134 ,  534 , or on the cavity or recess  142   a-b ,  542   a-b  side of the ground planes  133   a-b ,  533   a-b . High quality transition between the connector housing  110 ,  510  and the ground planes  133   a-b ,  533   a-b  (by the conductive elements  150   a-b ,  550   a-b ) as well as between the center pin  111 ,  511  of the connector housing  110 ,  510  and the conductive tab  134 ,  534  is necessary. Without the extra layers  546   a-b , in FIG. 5, a good mechanical support is hard to encounter. The whole support must then come from the bounding surface  517  between the connector housing  510  and stripline circuit  530 . With the extra layers  546   a-b  the non-conductive substance  520  is put between the side  518 ,  519   a-d  of end part  517  or between the side of the neck part (the tapered part of the housing  510 ) of the connector housing  510  and the extra layers  546   a ,  546   b , see especially in FIG. 5 the projected part D—D. Without the protruding parts  145   a-b  in FIG. 3 a , a good mechanical support is hard to encounter. The only support will be the terraces  144   a-b  that support the end part  117  of the connector housing  110  (on condition that the surface of the end part  117  of the connector housing  118  cover parts of the terraces  144   a-b ) the non-conductive adhesive substance  120  can be smeared on the parts of the end part  117  that is in contact with the terraces  144   a-b , avoiding non-conductive adhesive substance to be smeared on the stripline circuit. 
     Examples of different materials used in FIG. 1 in one exemplary embodiment of the invention see table TAB. 1. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                  Parts of one exemplary embodiment 
                 Type of material 
               
               
                   
               
             
             
               
                  First and second stiffening layer 
                 FR4 layer without copper 
               
               
                 141a-b, 541a-b 
               
               
                 First and second ground plane 
                 Copper layer (17.5 μm thick) 
               
               
                 133a-b, 533a-b 
               
               
                 First and second dielectric layer 
                 Microwave laminate RO3003 
               
               
                 132a-b, 532a-b 
               
               
                 Center conductive layer 131, 531 
                 Copper layer (17.5 μm thick) 
               
               
                 Tab 134,534 
                 R28046500 from RADIALL 
               
               
                 Adhesive substance 120, 520 
                 MVK89 AV138/HV998 from 
               
               
                   
                 CIBA 
               
               
                 Conductive element 140a-b, 540a-b 
                 Elastomer shielding gasket 
               
               
                 Coaxial connector 110, 510 
                 SMA type connector R125460001 
               
               
                   
                 from PADIALL 
               
               
                 Bondfilm 121 
                 6250 from ARLON 
               
               
                 Glue between ground plane 
                 NO-FLO PREPREG 
               
               
                 133a-b, 533a-b and stiffening 
               
               
                 layer 141a-b, 541a-b 
               
               
                   
               
             
          
         
       
     
     As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed.