US2995718A - Constant-impedance cable connector - Google Patents

Description

x- J. D. MURPHY 2,995,718

" CONSTANT-IMPEDANCE CABLE CONNECTOR Filed June 2, 1960 2 Sheets-Sheet 1 l I l 3o 3 5s Q5 5e t: f? ov I I r INVENTOR. JAMES D. MURPHY 8, 1961 Ju m. MURPHY 2,995,718

CONSTANT-IMPEDANCE CABLE CONNECTOR Filed June 2, 1960 2 Sheets-Sheet 2 mmvrox. JAMES 0. MURPHY United States Patent The present invention relates to an improved connecting device for coaxial cables of the type in which the insulating material disposed between the cable conductors, rather than being formed as a homogeneous solid, is instead composed of a plurality of layers of'some substance having suitable dielectric properties.

Many forms of connecting devices for coaxial cables are known in which both the electrical and mechanical requirements of the assembly are met by removing a portion of the inner dielectric material and arranging the conductive portions of the assembly so as to preclude any leakage of energy between the conductors and also to avoid any sharp mechanical discontinuities which might result inan undesirable increase in the standing wave ratio.

When coaxial cables of the type formed with a solid dielectric between the inner and outer conductors are to be interconnected, the problem of maintaining the electrical characteristics of the cable is not too difficult of solution; One expedient in common usage is to counter-bore the dielectric surrounding the center con ductor, and then to employ a relatively long pin or sleeve surrounding therespective terminal portions of the center conductor. However, such a process is not practicable in cases where the coaxial cables to be joined are manufactured with a dielectric in the form of an insulating tape which is wrapped around the center conductor so as to create a plurality of layers filling the space between the latter. and a braided metal outer conductor. With such cable constructions, it is apparent that the wrapped dielectric of the cable cannot be bored out by the same operation used in modifying a cable having a solid dielectric. Consequently, previously-known methods of interconnecting coaxial cables are not suitable for employ- .ment under these particular conditions.

Furthermore, it is highly desirable that any resulting alteration of the respective terminal portions-of two cables to be interconnected be such that each subassembly is capable of being quickly and easily inspected for mechanical uniformity prior to the time that the two units are joined together. arranged that tightening of the connector housing will not result in any change in the physical relationship of the elements of the connector assembly or in their electrical characteristics.

In accordance with a feature of the present invention, there is provided a constant-impedance high-voltage conncctor especially designed for use with wrapped-dielectric cables of the coaxial type, in which the electrical path between the respective conductors of each cable possesses avery low resistance factor, while at the same time mechanical discontinuities are eliminated Still further, each subassembly should be so Patented Aug. 8, 1961 conductor of the cable and with the inner surface of the sleeve or housing which encloses the connector components. The presence of such a collar at each cable terminal portion establishes a low-resistance electrical path between the respective outer conductors of the two cables to be interconnected, so that the loss factor of the assembly compares very favorably with many connectors conventionally employed to join together cables of the solid-dielectric type.

One object of the present invention; therefore, is to provide an improved connector for coaxial cables which are so designed that the insulation lying between the inner and outer cable conductors is made up of a plurality of wrapped layers.

' A further object of the invention is to provide a cable k connector of the above nature which acts to maintain the high-voltage breakdown characteristics of the cable, while at the same time precluding any appreciable increase in the standing-wave ratio thereof.

An additional object of the invention is to provide a p connector for wrapped-dielectric coaxial cables in which which, when present, are undesirable in the sense that into electrical engagement both with the outer tubular Y .which will be set forth hereinafter.

the connector components associated with each cable,

terminal portion may be quickly and easily assembled, inspected, and then the two cable terminal portions joined together without the interconnecting operation causing any significant alteration in the cables electrical characteristics.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein;

FIG. 1 is a partly sectional" view (with the housing member disengaged) of a connector subassembly designed in accordance with the principles of the present invention and intended for use at the terminal of one structed somewhat along the lines of FIG. 1, but intended for use at the terminal of the remaining cable portion to be interconnected;

FIG. 3 is a side view of one of the components of the connector subassembly of FIG. 1;

FIG. 4 is an end view of FIG. 3; and

FIG. 5 is. a side view of a still further component of the connector subassembly of FIG. 1.

Referring first to FIG. 1 of the drawings, there is shown one terminal portion of a coaxial cable 10 fabricated to include a center conductor 12, a braided metal outer conductor 14, and a series of layers of wrapped dielectric material 16 filling the space between the cable conductors. This dielectric material 16 may be of any suitable type which possesses both thinness and high insulating properties. For example, it may be inthe form of tape made from some plastic such as Teflon. Surrounding the outer tubular conductor 14 in conventional fashion is a layer of suitable insulation.

As shown in FIG. 1, the twoconductors 12 and 14 at the extremity of coaxial cable 10 are rendered accessible by removing a portion of both the inner and outer in-. sulating material of the cable. This permits the present invention to be practiced by the employment of means The outer cable conductor 14 is first stripped back and then bent in reverse fashion to encircle a clamp 18 adjacent to which is positioned an O ring, or rubber gasket, 20. All of the layers of insulating material 16 are then cut away for a short distance back from the end of the cable to allow the center conductor 12 thus exposed to project outwardly from a shoulder indicated in the drawing by the ing, the rubber gasket 20 lies between the cable clamp 18 and the inner shoulder of a threaded sleeve 24 which 'is formed integrally with a nut 26, the sleeve 24 being designed for engagement with the threaded inner surface of a more or less conventional housing member 28.

As above stated, the center conductor :12 of cable is initially exposed for a short distance back from the end thereof. A male pin 30, composed of electricallyconductive material, is designed with a sleeved portion 32 adapted to slip over the exposed end of conductor 12 in such a manner as to establish a tight-fitting relation therebetween, or, preferably, to permit these two elements to be soldered together. As shown in the drawing, the rear surface of the sleeve pin portion 32 abuts the shoulder 22 formed by removal of a portion of the cable dielectric material 16.

Encircling the pin 30 is a generally cylindrical bushing 34 which may be formed of the same dielectric material as that of the cable insulation 16 except that it is in one 4 remaining subassembly is illustrated in FIG. 2. Many of the elements of this latter figure are similar both in structure and function to those of FIG. 1, and consequently only those which possess significant variations will be discussed hereinafter. Such variations are found primarily in the surface configuration of a second bushing which mates with that of the bushing 34, and in the provision of a female pin associated with the center cable conductor, this female pin being designed to receive the male pin 30 of FIG. 1.

The bushing element of FIG. 2 is generally identified in the drawing by the reference numeral 56. ing incorporates a central section 58-substantaially identical to that of the central bushing section 36 of bushing piece rather than of tape form. As an illustration. the

bushing 34 mav be fabricated of Teflon which has been molded or machined to the configuration best shown in FIG. 5 of the drawings. That is. it possesses a central portion 36. of maximum outer diameter. having an axial openin in which the sleeved pin portion 32 is receivable.

. Longitudinallv offset from this central bushing portion 36 is a second section 38. of reduced outer diameter. and possessing a conical recess 39 the axis of which coincides with the rincipal axis of the bushing as best shown in FIG. 1. This recess 39 in the bushin section 38 is confi ured to receive a conical proiection formed as part of a further bushing to be hereinafter described in connection with FIG. 2.

Lying on the opposite side in a longitudinal sense of the central bushing portion 36 from that of bushing section 38'is a still further bushing section 40 which is of minimum outer diameter. this construction being again best shown in FIG. 5 of the drawings. This bushing section 40 is in the form of a tubular sleeve. and forms with the central bushing portion 36 a shoulder 42 designed to be in contact with the shoulder 22 of the dielectric material 16 when the components are assembled as shown in FIG. 1. The inner surface of the bushin section 40 (shown in FIG. "5 by the reference numeral 44) is adapted to fit tightly over the outer surface of the cables wrapped dielectric material 16. To position a collar 46 so that it encircles the outer surface 48 of the bushing portion 40. several layers of the ,wrapned dielectric material 16 are removed in this region to forma still further shoulder 50. the end surface 52 of the bushing sleeve 0 abutting this shoulder 50 in the manner brought out in FIG. 1. The collar 46 mentioned above is designed to fit snuglv over the bushin section 40 and to lie between the mid-portion 36 of the bushing and the turnedback outer cable conductor 14 in the manner illustrated.

Collar 46 is composed of material having high conductive characteristics. such, for example. as beryllium copper, and is shown in detail in FIGS. 3 and 4 of the drawings. It is designed with a flanged innerportion 54 which makes electrical contact with the outer cable conductor 14. this flanged inner portion 54 also making direct electrical contact with the inner surface of the shell or housing element 28 when the latter is brought into such position that the threaded inner surface thereof engages the threaded surface of the sleeve 24. When the components of FIG. 1 are assembled, the collar 46 will assume the position within the housing elemen-t28 indicated by the broken lines, the outer, or forward, end of the collar 46 being designed to lie in abutting relation with the central portion 36 of the bushing 34.

The preceding description of the components shown in FIG. 1 covers one of two subassemblies which together comprise the connector of the present invention. The

34. Bushing 56 also includes an inner sleeved portion 60 corresponding to the sleeved bushing portion 40 of FIGS. 1 and 5, and an outer conical section 62 the surface of which isjconfigured to fit within the conical recess 39 formed in the bushing section 38. When the two subassemblies of FIGS. land 2 are brought together and fastened in a manner to be later described, the recessed bushing section 38 of FIG. 1 will receive therewithin the conical outer bushing section 62 of FIG. 2 to form a solid dielectric mass extending between the collar 46 of FIG. 1 and a similar collar 64 associated with the assembly of FIG. 2.

To accommodate the male pin 30 of the unit illustrated in FIG. 1, there is shown in FIG. 2 a female pin 66 having an inner sleeved portion 68 which fits over the center conductor 70 of the cable 72 in the same manner that the sleeved pin portion 32 of pin 30 fits over the center conductor 12 of coaxial cable 10. This pin 66, however, is formed with a tubular terminal portion 73 which is split longitudinally by the slot 74 to thereby permit a tight fit to be established when the male pin 30 is received therewithin. It will be noted from the drawing that the length of the tubular terminal portion 73 of the female pin 66 is chosen to create a large area of electrical contact between the pins 30 and 66 and thus prevent any loss of energy which would cause the transmission efiiciency of the connector to be adversely affected.

In a manner similar to that in which the component assembly of FIG. 1 is receivable within the shell or housing element 28, the device of FIG. 2 is intended for insertion in a housing 76 having an innner threaded surface 78. The latter is designed for engagement with the outer threaded surface 80 of a sleeve which is associated with the terminal portion of cable 72 in the same manner that threaded sleeve 24 encircles the terminal portion of cable 10. Following such engagement, a tightening of nut 82 completes the subassembly of FIG. 2 and brings the collar 64 into a position as'shown by the dotted lines.

It has been stated above that the collars 46 of FIG. 1 and 64 of FIG. 2 act as media by which the respective outer cable conductors are electrically joined through the connector unit. To perform this function with maximum efficiency, the collars 46 and 64 are arranged not only to have excellent contact with their respective cable conductors, but also with the inner surface of their respective housing members. To achieve this result, each of the collars 46 and 64 is designed with a configuration best illustrated in FIGS. 3 and 4 of the drawings. Referring now to these latter figures, it will be seen that collar 46, for example, not only incorporates the previously-mentioned flanged inner portion 54, but is alsoprovided with a beveled outer flange 84 one surface of which contacts the inner surface of the housing unit 76 when each subassembly is in condition for a final interconnection. of the two cable portions 10 and 72.

The collar 46, as hereinabove stated, is receivable over the sleeve portion 40 of the bushing element 34, as shown in FIG. 1. To ensure a proper fit between these two components, the iner diameter of the collar 46 is essentially identical to the outer diameter of the This bushbushing portion 40. To allow for manufacturing tolerances, and to permit these elements to enter into slidable engagement with one another, and to permit positive contact between flnage 84 of the collar and the inner surface of housing unit 76, the collar 46, which is of generally tubular design, is provided with a plurality of longitudinal slots 86 which extend from the outer, or forward, portion of the collar 46 toward the flanged inner portion 54. This permits a limited degree of flexing of the electrically-conductive material of which .the collar is composed. The number of slots which are thus formed in the beveled outer flange 84 (see FIG. 4) will depend both on the diameter of the collar and upon the flexibility of the material used in its manufacture.

As an important feature of the invention, the diameter relationship of the inner and outer conductors are maintained throughout the connector subassemblies in the same ratio as they possess in cables and 72 thus providing constant impedance throughout the entire length of the cables and the connector., For this purpose, and as will be seen in FIG. 1, the inner diameter of collar 46 is so dimensioned that the ratio of that diameter to the diameter of center conductor 12 is equal to the ratio between the diameter of the inner surface of the outer conductor to the diameter of the central conductor in cable 10. The same ratio relationship is held between the diameter of sleeve pin portion 32 and the inner diameter of housing 28, and also between the diameter of male pin 30 to the inner diameter of housing 28. Similarly, the same ratios are held between the corresponding parts in the subassemblies shown in FIG. 2 as are held between the inner and outer conductors of cable 72.

It will be noted that only a minimum number of operations are required to complete the connector assembly of the present invention. After the cable has been properly trimmed to expose the center cable conductor 12 (for example) and the braided metal outer conductor 14 has been turned back in the manner shown by FIG; 1, approximately three layers of the wrapped dielectric material 16 are removed in the region where the sleeved bushing portion 40 will be received. The male pin 30 (in the assembly of FIG. 1) is then secured, preferably by soldering, to the center cable conductor 12. The collar 46 is positioned to encircle the sleeved bushing portion 40, and then the latter is slipped over that portion of the cable insulation which has been stripped away. In so doing, it follows that the central bushing portion 36 is caused to overlie the sleeved portion 32 of pin 30, and the outer bushing portion 38 positioned so that the terminal portion of pin 30 lies in the conical recess 39. The outer surface 48 of the sleeved bushing portion 40 consequently carries the collar 46 thereon, the inner surface 44 of this sleeved bushing portion 40 lying over and contacting that portion of the wrapped dielectric material 16 which had been previously stripped back.

All of the parts of each subassembly are inspected to ensure that they conform to the mechanical and electrical specifications laid down for the apparatus, and then the threaded portion 94 of shell or housing element 28 is brought into contact with the threaded sleeve 24 following which the nut '26 is tightened to complete this phase of the operation. In a similar fashion, the elements shown in FIG. 2 are assembled and inspected and then the housing unit 76 moved into a position which permits engagement between the threaded inner surface 78 of the housing unit 76 and the threaded outer surface 80 of the cable sleeve. Tightening of the nut 82 then completes this subassembly.

The two units thus assembled are brought into proximity with one another and then the male pin 30 inserted in the tubular terminal portion 73 of female pin 66. At the same time, the recess 39 in bushing section 38 receives the conical projecting portion 62 of bushing 56,

while the threaded outer surface portion 88 of housing 76 comes into engagement with the threaded inner portion of end portion 92 of the housing 28. As shown in FIG. 1, end portion 92 is rotatable relative to the balance of housing 28. In the above assembled position, rotation of end portion 92 will engage threaded portions 88 and 90 to result in a tight fastening of housing element 28 to housing element 76, together with good electrical contacting engagement of their corresponding elements as described above.

It will be noted that tubular bushing section 40 lies within collar 46 and serves to close the minimum distance path between the upper end of sleeve 32 and the conductor collar 46 at the joint between bushing 34 and insulating material 16. With the bushing section 40 in place in the assembled condition, the electrical leakage path between conductive sleeve 32 and conductive collar 46 is lengthened appreciably to a course from the upper end of sleeve 32 along the joint at shoulder 22, thence upwardly along the inner surface of upstand-bushing section 48 and along the joint at shoulder 50 to conductive collar 46 thus providing minimum electrical energy loss. This characteristic is of particular importance since it enables my invention to be used as a connector on high-voltage cables. Thus, the high-voltage, constant-impedance connector described above is superior to other constant-impedance connectors now available which do not have the high-voltage characteristic described above.

While operating results will depend at least in part on the dimensions of the connector components and on the materials used in their construction, it may be mentioned purely as an example that in one particular assembly, designed in accordance with the above teachings, voltage standing wave ratio measurements were made over a range of 400 to 6000 megacycles, with the highest reading being 1.5: l at 5000 me. v

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A connecting device for coaxial cables of the type in which the insulating material disposed between the cable conductors is made up of a plurality of layers of a dielectric substance, and in which such dielectric substance is stripped back from the terminal portion of each of the cable sections to be connected, said device comprising a pair of connector subassemblies respectively associated with the said terminal cable portions, one of said subassemblies incorporating a pin having a sleeved extension encircling the teminal portion of the center conductor of the cable section with which the said subassembly is associated, a dielectric bushing composed of homogeneous material and having three sections the intermediate one of which is adapted to encircle the sleeved extension of said pin and one end section which is adapted to encircle the multilayer insulation of said cable in the region where one or more layers of such insulation have been stripped back, this particular end section of said bushing thus being of tubular configuration, the remaining end section of said bushing substantially enclosing the outer portion of said pin and having a conical recess axially formed therein, a collar of electrically-conductive material and of generally annular shape designed to encircle that particular bushing section which overlies the stripped-back portion of said cable dielectric, said collar having a rear wardly-positioned shoulder for electrical engagement with the tubular outer conductor of said cable and a forwardly-positioned shoulder for engagement with the mid-section of said bushing, a housing for said subassembly one portion of which is secured to said cable and a further I portion of which is adapted for threadable engagement with said one portion, whereby threadable engagement between the two said housing portions results in the 7 establishment of electrical contact between said collar and the inner surface of said housing, the second of the two said connector'subassemblies including a pin having inner and outer sleeved portions, the former being designed to encircle the terminal portion of the center condoctor of the cable section with which such second subassembly is associated, the remaining sleeved portion of said pin being adapted for electrical engagement with the outer portion of the pin incorporated in said first subassembly when the connecting operationis carried out, a bushing of electrically-insulating material having a midportion designed to encircle the inner sleeved portion of said pin and an end portion of tubular configuration designed to encircle that region of said cable dielectric which has been stripped back, the remaining end portion of said bushing being of conical shape andadapted to be receivable in the conical recess formed in the bushing member of said first subassembly, a collar of electrically eonductive material encircling the tubular portion of saidibushing, said collar being of annular configuration and having a pair of shoulders the rearward one of which is adapted for electrical engagement with the outer conductor of said cableand the forwardly-positioned one of whichis adapted to engage the mid-portion of said bushing, a tubular housing for said second subassembly, said housing having a portion secured to said cable and a further portion adapted for threadable engagement therewith and also for threadable engagement with the housing of said first subassembly, whereby such a threadable engagement of the housings respectively associated with the two said subassemblies will establish electrical contact between the respective inner cable conductors through the two said pins and between the outer cable conductors through their respective housing portions and through the collars respectively associated with each of the two said subassemblies.

2. A connecting device in accordance with claim 1, in which the collars respectively associated with each of the two said subassemblies are each designed with a plurality of longitudinal apertures permitting a limited degree of flexing of said collar when the latter is brought into a position where it encircles that tubular portion of its respective bushing which is designed to overlie the stripped-back region of said cable dielectric.

References Cited in the file of this patent

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