Apparatus for connecting transmissions paths

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] Specifically, the problem is solved by the coaxial connector according to claims 1 and 7.

[0010] 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.

[0011] Another object is to provide good mechanical connection between the coaxial connector and the stripline circuit.

[0012] 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.

[0013] 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.

[0014] Another advantage is that a good mechanical connection between the coaxial connector and the stripline circuit can be attained.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] FIG. 1ais an enlarged part of FIG. 1 illustrating the conductor tab.

[0019] FIG. 1bis an enlarged part of FIG. 1 illustrating one conductive element.

[0020] FIG. 1cis an enlarged part of FIG. 1 illustrating the stripline circuit.

[0021] FIG. 2ais 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. 3a.

[0022] FIG. 2bis 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. 3d.

[0023] FIG. 2cis a projected part A—A of FIG. 1, illustrating the conductive elements and a part of the stiffening layers corresponding to FIGS. 3a-dand FIG. 5.

[0024] FIG. 3ais a perspective view of a part of FIG. 1, illustrating the stripline circuit and a first embodiment of the stiffening layers.

[0025] FIG. 3bis a perspective view of a part of FIG. 5, illustrating the stripline circuit and a second embodiment of the stiffening layers.

[0026] FIG. 3cis a perspective view of a part of FIG. 1, illustrating the stripline circuit and a third embodiment of the stiffening layers.

[0027] FIG. 3dis a perspective view of a part of FIG. 1, illustrating the stripline circuit and a fourth embodiment of the stiffening layers.

[0028] FIG. 4ais 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.

[0029] FIG. 4bis 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.

[0030] 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.

[0031] FIG. 5ais 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.

[0032] 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.

[0033] 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.

[0034] The conductive tab 134, in FIG. 1a, 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 133a, a first dielectric layer 132a, a center conductive layer 131 including two layers 131, 121 see FIG. 1c, a second dielectric layer 132b, and a second ground plane 133b. Normally the stripline circuit 130 in FIG. 1cis obtained from two dielectrics layers 132a-bmade of e.g. microwave laminate. On each side of one of the dielectric layer 132aa conductive plane 133a, 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 133a. The second dielectric layer 132bwith one conductive plane 133bis glued together with the part opposite the ground plane 133b, with e.g. a bond film 121 to the etched conductive plane 131. The conductive plane 133bof the second dielectric layer 132bis now the second ground plane 133b, and the etched conductive plane 131 is forming the center conductive layer 131. Before gluing the two dielectric layers 132a-btogether, 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 132a-bare glued together with the bond film 121, the etched conductive layer 131 with the side of the second dielectric layer 132bwhich is opposite of the second conductive plane 133b, 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.

[0035] The first and second dielectric layers 132a-bare 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 133a-b. The stripline circuit 130 including the ground planes 133a-band dielectric layers 132a-band center conductive layer 131 can be made of soft material so that it is necessary to put one stiffening layer 141ato the first ground plane 133a, and another second stiffening layer 141bto the second ground plane 133b. The stiffening layers 141a-bare 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 141a-bare e.g. with NO-FLO PREPREG glued together with the ground planes 133a-b.

[0036] A first stiffening layer 141ais attached to the first ground plane 133a, a cavity 142a, 143a; 142a, 145ais formed in the first stiffening layer 141aso a first conductive element 150acan be provided in the cavity 142a, 143a; 142a, 145asee different form of cavities 142a, 143a; 142a, 145a; 142b, 143b; 142b, 145bin the stiffening layers 141a-b.

[0037] 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. 4atogether with FIG. 1 or 5, or e.g. round as can be seen in FIG. 4btogether with FIG. 1 or FIG. 5. The rectangular end part 117 in FIG. 1 or 5 together with FIG. 4ahas four sides 119a-d(corresponding to 519a-din FIG. 5, where only 519a-bis shown) and the round end part 117 in FIG. 1 or FIG. 5 together with FIG. 4bhas 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 141a-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.

[0038] If the first stiffening layer 141aand second stiffening layer 141bare elongated so as to protrude above the stripline circuit 130, 135 as can be seen in FIGS. 3a-d, the protruded parts 145a-bcan support the connector housing 110. In the first embodiment in FIG. 3aa terrace 144a-bis formed in between the remaining protruded parts 145a-bof the first and second stiffening layers 141a-b, and the cavity 142a, 143a; 142b, 143b. The end part 117 of the connector housing 110 may then get extra support from the terraces 144a-bin the case where the surface of the end part 117 has a size allowing it to be in contact with the terraces 144a-b. In the projected view of FIG. 1, FIG. 2aB—B, the connector housing 110 is in contact with the terraces 144a-bas can be seen as the elongated side 119a-bthat form a rectangular end part 117 over the edge 143a, 143bof the cavities 142a, 143a; 142b, 143b. In the second embodiment in FIG. 3bthe form of the stiffening layers 145a-bresult 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. 3bcorrespond to FIG. 5 where the stiffening layers 141a-b, 541a-bhave attached extra layers 146a-b, 546a-b. The end part 117, 517 must have a surface big enough so the conductive elements 150a-b, 550a-bis in contact with the end part 117, 517. In the third embodiment in FIG. 3csimilar to FIG. 3b, where the difference is that beside the cavity 142a, 145a; 142b, 145bformed in between the first ground plane 133aand the first stiffening layer 132aand second ground plane 133band the second stiffening layer 132b, an extra bulge 147a, 147bis formed in the first and second stiffening layer 141a-b. The end part 117 of the connector housing 110 has its support from the stripline circuit 130 and the bulge formed terraces 144a-b. A connector housing 110 with a round formed end part 117 as can be seen in FIG. 4bis necessary. For the bulge form 147a, 147bside to be of any support for the connector housing 110, the side 118 of the connector housing 110 should fit into the bulge 147a, 147bor leave a small space in between, see the adhesive substance 120 in the circle in FIG. 2bB—B. Actually the projected view in FIG. 2bB—B shows the embodiment in FIG. 3dwhere the stiffening layers 141a-bare adjacent to the ground planes 133a-band the cavities 142a, 143a; 142b, 143bare more or less hidden. The end part 117 fit into the bulge part 147a, 147bin FIG. 3d, and the bulge formed terraces 147a, 147bsupport the end part 117 as in FIG. 3c. As will be recognized by those skilled in the art, e.g. drilling, or cutting can be used in making the cavities 142a, 143a; 142b, 143band protruding parts 145a, 147a; 145b, 147bor the formation in the stiffening layers 141a-bcan be made in the assembly of the stripline circuit 130.

[0039] Returning to the conductive elements 150a-bshown respectively in a slit 142a, 143a; 142b, 143bin FIG. 1 or as shown in FIG. 5 the conductive elements 550a, 550bare placed in a recess 542a, 542bof the stiffening layers 541a, 541b. In FIG. 1 is illustrated together with the projected view A—A in FIG. 2cthat the conductive elements 150a, 150b, 550a, 550bare 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 542a, 542bin FIG. 5 or the slits 142a, 143a; 142b, 143bin 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 133a-b, 533a-b. In FIG. 5 the conductive element 550acan protrude out a bit from the recess 542awhen no extra layer 546ais fixed next to the side of the first stiffening layer 541a. A mechanical improvement is obtained with the extra layers 546a-bas illustrated in FIG. 5 fixed adjacently towards the side of the first and second stiffening layers 541a-bcompared to an embodiment without them.

[0040] As will be recognized by those skilled in the art the recess 542a, 542bin FIG. 5 or cavity 142a, 143a; 142b, 143bin FIG. 1 together with FIGS. 3a-dmay have any shape, to provide the conductive elements 150a-b, 550a-bthat 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 133a-b, 533a-b. Dependant on the type of connector housing 110, 510 used in the embodiment, the form of the protruded part 145a-b, 545a-bof the stiffening layer 141a-b, 541a-bmust be adjusted accordingly. For example a bulge form 147a, 147billustrated in FIGS. 3c-dis 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. 4a.

[0041] In FIG. 2bB—B a projected view shows the protruding parts 145a-bformed as a circular hole 147a-bwith 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 145a-b, 147a-b. In FIG. 2aB—B a projected view illustrates an elongated opening. The elongated opening of the protruded parts 145a-bis filled with the adhesive substance 120 between the protruded parts 145a-band the side 118, 119a-dof the connector housing 110. It is eligible that the adhesive substance 120 is applied between the edge 118, 119a-dof the connector housing 110 and the protruding parts 145a-bof the stiffening layers 141a-band not smeared on the end part 117 of the connector housing 110. In cases where at least one side 118, 119a-dof the end part 117 of the housing 110 is adjacent to the protruded stiffening layers 145a-b, 147a-bthe adhesive substance 120 must be put where the adhesive substance 120 can be in contact with the connector housing 110 and the protruding sides 145a-b, 147a-b, e.g. above the side 118, 119a-dof the connector housing 110, between the neck part (the tapered part of the housing 110) of the housing 110 and the protruded stiffening layers 145a-b, 147a-b. In this way the adhesive substance 120 will be functioning as an embedment for the connector housing 110 between the protruding parts 145a-bof the stiffening layers 141a-bat the same time as it is fixing the connector housing 110 to the stiffening layers 141a-b. A preferred embodiment for the stiffening layers 141a-bare to include a terrace 144a-bin between the remaining protruding part 145a-band the cavity 142a, 143a; 142b, 143bfor best support of the end part 117 of the connector housing 110, as in FIGS. 3a, 3c-d.

[0042] 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 145a-b, 147a-bof the first and second stiffening layers 141a-babove the stripline circuit 130 surface 135 in FIG. 3aand no extra stiffening layers 546a-bare attached to the first and second stiffening layers 541a-bin 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 133a-b, 533a-band first and second dielectric layers 132a-b, 532a-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 142a-b, 542a-bof the ground planes 133a-b, 533a-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 142a-b, 542a-bside of the ground planes 133a-b, 533a-b. High quality transition between the connector housing 110, 510 and the ground planes 133a-b, 533a-b(by the conductive elements 150a-b, 550a-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 546a-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 546a-bthe non-conductive substance 520 is put between the side 518, 519a-dof 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 546a, 546b, see especially in FIG. 5 the projected part D—D. Without the protruding parts 145a-bin FIG. 3a, a good mechanical support is hard to encounter. The only support will be the terraces 144a-bthat 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 144a-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 144a-b, avoiding non-conductive adhesive substance to be smeared on the stripline circuit.

[0043] Examples of different materials used in FIG. 1 in one exemplary embodiment of the invention see table TAB. 1.

[0044] 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.