US3458852A - High power microwave coaxial cable connector - Google Patents

Description

3 Sheets-Sheet l July 29, 1969 E. F. HIGGINS, JR

HIGH POWER MICROWAVE COAXIAL CABLE CONNECTOR Filed April 4, 1967 Jul-Y 29, 1969 E. F. HIGGINS, JR 3,458,852

HIGH POWER MICROWAVE COAXIAL CABLE CONNECTOR Filed April 4. 1967 3 Sheets-Sheet 2 July 29, 1969 E. F'. HIGGINS, JR 3,458,852

HIGH POWER MICROWAVE COAXIAL CABLE CONNECTR Filed April 4. 1967 3 Sheets-Sheet 3 United States Patent Olce Patented July 29, 1969 U.S. Cl. 339-177 8 Claims ABSTRACT OF THE DISCLOSURE together and (2) carrying the cable core an `appreciable distance inside the connector dielectric material with a tight, interfering lit, thereby both increasing the breakdown path length and substantially excluding all gas from between the cable core and the connector dielectric.

Background of the invention This invention relates to coaxial electrical connectors and more particularly to a high power connector capable of operation at microwave frequencies under very low ambient pressures.

Many prior art coaxial connectors exist for microwave applications at normal atmospheric pressures and some of these are quite reliable at these pressures. However, operation at low ambient pressures presents a very special problem because air ionizes so readily at low pressures that breakdowns occur at quite low power levels. The problem becomes very much more acute when it is essential that the connector withstand a high voltage. Coaxial connectors have been made with special seals to maintain near atmospheric pressures within their enclosures but they frequently leak and breakdowns result.

Summary of the invention The connector of this invention comprises a plug part and a receptable part, each containing a center conductor coaxial with an outer conductor, the intervening space being completely iilled with a solid dielectric material. Both conductors are tapered to provide a larger diameter at the mating interface where the plug and receptacle parts are joined. High power capability under low ambient pressures is made possible by 1) providing the mating surfaces of the dielectric materials in both parts with cornplementary conical shapes dimensioned to engage with a tight it to substantially exclude all gas as the two parts are coupled together and (2) carrying the cable core an appreciable distance inside the connector dielectric with a tight, interfering tit, thereby both increasing the path length along their interface and substantially excluding all gas from between the cable core and the connector dielectric.

In one embodiment of the invention, the conical shape of the dielectric comprises an annular groove in the mating surface of one of the connector parts while the other connector part has a complementary annular ridge on its dielectric material to closely iit in the groove as the two connector parts are coupled together.

In another embodiment, the conical shapes comprise an internal conic surface in the dielectric material of the plug part and a complementary external conic surface 0n the dielectric material of the receptacle part, these surfaces coming together with a tight, interfering t as the connector parts are coupled together.

Brief description of the drawings The invention may be better understood by reference to the accompanying drawings in which:

FIGS. 1 and 2 disclose receptacle and plug parts, respectively, of a connector embodying the principles of this invention;

FIG. 3 discloses fragmentary views of the plug and receptacle parts of another connector embodying the principles of this invention; and

FIG. 4 discloses the invention as embodied in FIG. 2 except that a bend is introduced in the enlarged end of the connector part.

Detailed description FIG. l discloses the invention embodied in the receptacle part of the connector. An inner or center conductor 1 is shown coaxial with an outer conductor or shell 2, the intervening space between these two conductors being substantially completely lled by a suitable solid dielectric material 3. While the material of which the dielectric is made is not particularly critical, it should, of course, be compatible with the environmental conditions under which the connector is to be used and it should be sufficiently pliable to effect a very close t at its interface with the dielectric of the plug part with which it is to be connected. Applicant has found that materials having an elastic modulus of about 2.6X pounds per square inch work quite satisfactorily. Moreover, the dielectric material should have dimensional stability over the working temperature range. Materials commercially available which meet these requirements are Teflon and Epen-919. More will be said about these materials with reference to the several embodiments to be described.

A conventional coaxial ca-ble having a center conductor 4, an insulating core 7 and a braided outer conductor 8 is shown brought into the right end of the receptacle part. The braid 8 is stripped back in accordance with conventional practice and the core 7 is stripped from the center conductor to expose the bare end 5, the extreme end of which is preferably rounded as at 6 to facilitate its entry into the bore hole 18 in the center conductor 1 of the receptacle part. Part way inside the bore hole 18 it has an enlarged diameter to form recess 13 to receive a suitable contact spring 14 which is inserted in the open end of the .bore hole 18 and permitted to expand and snap in place in recess 13. Contact spring .14 makes elastic contact with the bare end 5 of the coaxial cable center conductor. The use of a contact spring is preferred over soldering for two reasons. First, it facilitates easy separation of the cable from the connector part without heat and second, it permits the center conductor to slide back and forth when stresses are applied to the cable, the stresses being assumed by the braid 8. If the stresses were to be borne by the center conductor, it could cause either breakage of the soldered joint or damage to the cable core 7.

The dielectric material 3 has an inner cylindrical portion 25, a conically tapered portion 26 and an outer cylindrical portion 27. The length of the inner cylindrical portion 25 is substantially coextensive with the length of the inner cylindrical portion 15 of the center conductor 1, terminating rather abruptly along line 32 opposite the end 17 of the center conductor. The ratio of the diameters of parts 15 and 25 is such as to provide the same characteristic impedance as that of the coaxial cable, thereby preventing undesirable reflections. Likewise, the ratio of the diameters of the tapered portion 19 of the center conductor and the conical interface' between dielectric portion 26 and the shell 2 is a constant for the entire -tapered length, this ratio also providing the same characteristic impedance as that of the cable. When the connector parts are assembled, this same condition exists for the outer cylindrical portion 27 and the outer portion 20 of the center conductor.

Before assembling the coaxial cable t the connector, a portion of the end of the cable core 7 is machined away from the center conductor 4 to receive the outer end of the center conductor of the connector. The interface between conductor 15 and the remaining part of core 7 after assembly is shown at 16. The hole in theI outer end of the cylindrical portion 25 of the connector dielectric material is also given a larger diameter to accommodate the outside diameter of cable core 7. In actual practice, the enlarged hole in portion 25 is given a slight taper with the hole getting smaller in diameter at its inner end. This provides an interfering fit with the outer end of the cable core 7 so that, as the cable is driven into the connector, there will develop a tight fit between the cable core and the inside surface of the opening in the dielectric portion 25. This fit will effectively exclude all gas over an appreciable length of the interface between the core and the dielectric material. Moreover, the fact that the cable core has been carried into the dielectric material, a longer breakdown path has been created between inner conductor portion 15 and the outer conductor or shell 2. This longer path and the exclusion of gas along this path cooperate to greatly increase the breakdown strength of the connector at this point.

After the coaxial cable has been driven into the connector in the manner described, the braid 8 may be carried over the jacket sleeve 11 and secured as shown at 9 to the sleeve by crimping a ferrule 10 thereover. If desired, a shrinkable insulating sleeve, not shown, may be brought over the anchor ridges 12 and shrunk thereon.

Tapered portions 19 and 26 and the tapered inside surface of outer conductor 2 are frustums of cones beginning at plane 22 and ending at plane 23. The outer cylindrical portion 27 of the dielectric materials begin at plane 23 and ends at the surface 24 of the receptacle part of the connector. An annular groove 28 is formed in the surface of the dielectric material, the surface portion 28A of which is defined by a cone having its apex at the left of surface' 24 and its axis coinciding with the axis of the center conductor 1. Portion 28B is also defined by a cone which intersects the cone defining portion 28A, its axis coinciding with that of center conductor 1 but having its apex to the right of surface 24. The conically tapered portions 19 and 26 provide a larger diameter at the front surface 24 to make ample room for groove 28, thereby both increasing the radial breakdown path length as well as providing means for excluding gas along a significant part of the mating interface between the connector parts when they are coupled together.

FIG. 2 shows a plug part that may cooperate with the receptacle part of FIG. 1 to complete the connector. This plug part comprises a center conductor 51 coaxial with an outer conductor 52, the intervening space being filled with the dielectric material 53. In this figure, the coaxial cable is secured to the plug connector part in a different manner but nevertheless embodying the same principles as those employed in FIG. 1. lt is to be understood that these are alternative methods and that either may be used interchangeably. In FIG. 2, the tapered portion 76 of the dielectric material is brought down to the outer surface of the cable core 57, meeting the cable at plane 72. The taper of the dielectric material begins at plane 72 and extends to plane 73 where the dielectric material continues in the cylindrical portion 77. The center conductor 51 is in two parts, the first part starting wtih the cylindrical portion 70 and abruptly changing to the tapered portion 69 at plane 73. The second part is the tapered portion 65 which may, for convenience', be termed the compensator.

To assemble the cable in this connector, 1ts center conductor 54 is stripped of its braid 58 and insulating core 57 for the short distance extending from the large end of compensator 65 to its rounded end 56. A conical portion 66 of the core 57 is then machined away from around the conductor to receive' the compensator 65. The compensator is then slipped over the end of the cable conductor to the position shown in FIG. 2 and carefully sweated to the conductor 55 with soft solder. The cable is then inserted in the connector body or shell 52 after which the dielectric material 53 and the center conductor 51 are forced in to the positions shown. Note that the small diameter end of the dielectric material 53 has a substantially cylindrical hole extending inwardly to the larger end of compensator 65 where it intersects with the conic surface of the inner conductor. The diameter of this hole presents a snug fit to the outer surface of cable core 57. As these parts are forced together, the dielectric material very closely conforms to the outer periphery of the cable core 57, forcing out virtually all gas from between them. The breakdown path length extends from the larger end of compensator 65 to the vicinity of plane 72 and this increased length and the exclusion of gas cooperate to greatly increase the breakdown strength in this part of the connector. The smaller end of the tapered portion 69 of the center conductor 51 is bored out at 68 to receive the stripped end 55 of the center cable conductor and the outer end of the bore hole is enlarged to form the recess 63 to accommodate a conductive insert 64. This insert is a pliable composition containing many small metallic spheres and is quite readily penetrated by the center conductor 55 to complete electrical connection through contact between the many small spheres. After assembling the cable to the connector in the manner described, the cable braid 58 is brought over the flanged braid sleeve 61 and secured as at 59 by a crimped ferrule 60. Nut 67 is then brought over the ferrule to engage the threads 84 and secure the flange 62 against the left end of shell 52.

At the mating surface of the plug part, the shell 52 continues with the annular portion 79 which is adapted to enter the annular space 29 of the receptacle part of FIG. l. The connector is secured together by knurled nut 82, the threads of which engage their complementary threads 30 of the receptacle part. Nut 82 is captivated by a conventional retaining ring 83. The receptacle part may be conveniently held from turning by grasping its knurled portion 31 while knurled portion 81 serves this purpose for the plug part. The dielectric material 53 of the plug part has an annular ridge 78 adapted to enter the annular groove 28 of the receptacle part. Ridge 78, like groove 28, is also defined by two intersecting cones. The center conductor of the plug part has a split prong 71 adapted t0 engage the complementary receptacle 21 in the center conductor 1 of the receptacle part. As the two connector parts are brought together under the force applied by nut 82, the annular shell part 79 fills the space 29 and its end surface 74 firmly engages a pliable conductive gasket 38 bottomed in space 29 of the receptacle part. This gasket insures good electrical connection between the shell parts. At the same time, conical surfaces 78A and 78B of ridge 78 engage their complementary conical surfaces 28A and 28B, respectively, of annular groove 28. As the parts are forced together, these surfaces, being somewhat pliable, closely conform to each other to effectively exclude substantially all gas from between their contact surfaces. It will be noted that the outer end of annular ridge 78 is slightly flattened to ensure that ridge 78 will seat firmly with groove 28. This will leave a small space at the flattened portion of ridge 78 which will entrap some gas but this gas will be above atmospheric pressure and extends over only a very small part of the entire radial distance between the inner and outer conductors. Because of the pressure maintained in this entrapped gas, it will not ionize under potential gradients to which it will ordinarily be subjected even though the outside of the connector is in a very W pressure atmosphere. Because of the annular groove and ridge, the radial breakdown path extending between the inner and outer conductors of the connector is considerably increased, amounting to about eighty-five percent for the proportions shown in FIGS. 1 and 2. While FIGS. 1 and 2 are not to exact scale, they do approximate the true relative proportions of an enlarged cross section view of a practical embodiment of the invention. As is well known, the exact taper angle to be given to the tapered portions 26 and 76 of the dielectric materials is governed by the dielectric constant of the material selected.

FIG. 3 shows an alternative embodiment of the invention in which the mating surfaces are enlarged by the tapered dielectric portion 26 between the tapered center conductor portion 19 and the tapered portion of the shell 2. The details of the tapered portions of both connector parts and the manner of bringing the coaxial cables into the connector are the same as described -for FIGS. l and 2. The plug part is shown on the left in this figure and the receptacle part is shown on the right. The center conductor -51 of the plug part terminates in a split prong 71 which cooperates with the receptacle 21 in the center conductor of the receptacle part in the same manner described for FIGS. l and 2. Surrounding the center conductor of the plug part is the dielectric material 53 which has a conical inside surface 34, corresponding with the inside conical surface 78A of FIG. 2. This inside surface 34 engages the complementary conical outside surface 33 of the receptacle part with a tight, interfering t just as was described for surfaces 28A and 78A of FIGS. 1 and 2. It is evident that when the connector parts are coupled together, the complementary conical surfaces 33 and 34 are defined by a single cone symmetrically disposed about the principal geometric axis of the connector. As the two parts of FIG. 3 are brought together, the front surface 74 of the plug shell enters the annular space surrounding the dielectric material 53 to engage the conductive gasket 38. Contact springs A37 of the plug part engage the inner surface of receptacle shell 79. As the connector parts are forced together, surfaces 33 and 34 conform and force out substantially all gas from between them. This is aided by the inside cylindrical surface 35 of the receptacle part which supports the outer surface 36 of the dielectric material in the plug part. An annular anchor ridge 39 is formed integral with the outer cylindrical surface of the inner conductor 1 to engage a complementary groove formed in the inner surface of the dielectric material 3. This ridge anchors the center conductor against being drawn out as the connector parts are separated.

FIG. 4 shows a plug part with the body or shell bent through an angle of about forty-five degrees. This figure otherwise is identical with the embodiment shown in FIG. 2 and the reference numerals of corresponding parts are the same in both figures. The method of introducing the dielectric material, however, is different. The dielectric material in FIGS. l, 2 and 3 may be machined from a solid block of material before assembly. However, in the embodiment shown in FIG. 4, the bend makes this impossible. In this case, the dielectric is molded into shell 52 with the center conductor 51 in place. Ridge 78 could be included in the mold, but it is preferably machined after molding to insure precision. While a 'bend of fortyve degrees is illustrated, other angles, e.g., a right angle, are as easily constructed. It will be quite evident that two mating parts, each bent as shown in FIG. 4, can be assembled to complete a ninety degree turn or the parts may be rotated at their mating surfaces to establish a variety of angular relationships including a straight angle with an axial offset. Moreover, these bent units may be mated with a straight receptacle part such as shown in FIG. 1 or other ones having different angular bends, such as the right angle bend previously mentioned.

From the several embodiments described above, it is quite evident that various other embodiments employing the principles of this invention will be obvious to those skilled in this art and these should be considered within the scope of this invention.

What is claimed is:

1. A high power microwave coaxial cable connector comprising a plug part and a receptacle part, each part containing an inner conductor and an outer conductor arranged as a coaxial pair with means for electrically connecting the inner and outer conductors of one part to the inner and outer conductors, respectively, of the other part, the portions of the common lengths of said two conductors of each part being in the shapes of conic frustums, a solid dielectric material substantially filling the entire space between the conductors of each part, the portion of said dielectric material at the larger diameter ends of the conductors of each part being exposed, the exposed portion of the dielectric material of one of said parts having a surface defined by a cone whose axis coincides with the axis of said coaxial pair, a conic surface on the exposed portion of the dielectric material of said other part being complementary to that of said one part so that, as the connector is assembled, said conic surfaces engage with a tight fit to exclude substantially all gases, means for connecting a coaxial cable to each of said parts, said means including an opening in said dielectric material concentric with the `axis of said coaxial pair to receive a substantial length of the insulating core of a coaxial cable with a tight t to exclude substantially all gases.

2. The combination of claim 1 wherein the surface of the exposed portion of the dielectric material in each of said parts is defined by two intersecting cones having axes coinciding with the axis of said coaxial pair, the intersecting cones defining a groove in the surface of one of said parts and a complementary ridge on the surface of the other of said parts.

3. The combination of claim 1 wherein the surface of the exposed portion of the dielectric material in one of said parts is an inside conic surface of the exposed portion in the plug part and the complementary conic surface of the dielectric material of said other part is an outside conic surface of the receptacle part.

4. The combination of calim 1 wherein said means for connecting a coaxial cable to each of said parts comprises a cylindrical portion of said dielectric material extending from the smaller diameter ends of said two conductors, said opening in the dielectric material entering from the outer end of said cylindrical portion and tapering to a smaller diameter at its inner end, said smaller diameter being such as to present a tight t to the outer surface of the core of a coaxial cable with which the connector part is to be assembled.

5. The combination of claim 1 wherein the opening in said dielectric material to receive the insulating core of a coaxial cable is substantially cylindrical and extends inwardly from the smaller diameter ends of said two conductors and terminates at the plane of its intersection with the conic surface of said inner conductor.

6. A high power microwave coaxial cable connector having a plug part and a receptacle part, each part containing an inner and an outer conductor arranged as a coaxial pair with a solid dielectric material substantially filling the space between them, characterized in that the mating surfaces of said parts have a diameter larger than that of the coaxial cables they are to connect, the portions of the dielectric material of said parts at their mating surfaces have complementary conical shapes dimensioned to engage with a tight fit to substantially exclude all gas as the connector is assembled, said dielectric material contains a cyclindrical opening to receive a substantial length of the insulating core of a coaxial cable with a tight fit to substantially exclude all gases, and the ratio of the diameters of said inner and outer conductors is substantially constant throughout the lengths of said connector parts to give said connector substantially the same characteristic impedance as that of the coaxial cables to which they connect.

7. The combination of claim 6 wherein the complementary conical shapes of said dielectric material are dened by two intersecting cones which dene a groove in the surface of one of said parts and a complementary ridge on the surface of the other part.

8. The combination of claim 6 wherein the comple rnentary conical shapes of said dielectric material are defined by a single cone having its axis symmetrically disposed about the principal geometric axis of the connector.

References CitedV DAVID I. WILLIAMOWSKY, Primary Examiner 10 J. KARL BELL, Assistant Examiner U.S. C1. X.R.

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