US3209287A

US3209287A - Electrical coaxial cable connecting assembly with impedance matching

Info

Publication number: US3209287A
Application number: US48534A
Authority: US
Inventors: Edwin S Oxner
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1960-08-09
Filing date: 1960-08-09
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28

Description

p 1965 E. s. OXNER ET AL 3,209,287

ELECTRICAL COAXIAL CABLE CONNECTING ASSEMBLY WITH IMPEDANCE MATCHING Flled Aug. 9, 1960 2 Sheets-Sheet 1 w \\\\V\VVWvW Wvv vv,m mvvvvV/r H/////////////////////////////////N Sept. 28, 1965 E. s. OXNER ET AL 3,209,287 ELECTRICAL COAXIAL CABLE CONNECTING ASSEMBLY WITH IMPEDANCE MATCHING Filed Aug. 9, 1960 2 Sheets-Sheet 2 E E N mmwb Q l H United States Patent ELECTRICAL COAXIAL CABLE CONNECTING ASSEMBLY WITH IMPEDANCE MATCHING Edwin S. Oxner, Menlo Park, Calif., assignor, by inesne assignments, to The Bendix Corporation, Detroit,

Mich., a corporation of Delaware Filed Aug. 9, 1960, Ser. No. 48,534 8 Claims. (Cl. 333-34) The present invention deals with electrical connectors and more particularly, is directed to the multi-conductor or coaxial type connector assembly.

Up to the present time most coaxial connectors have required fanning of the cable braid in the normal assembly procedure. A technique to obviate the fanning process is a special clamping device in the form of two sleeves which are passed under and over the cables outer conductor and then stamped, under extreme pressure, by a stamping machine. In both of the types mentioned a gasket must be included at the rear of the connector to effect a water seal. Furthermore, the second type 'of connector mentioned is not reusable. That is to say, the stamped sleeve must be replaced since it is permanently affixed to the coaxial cable.

In the case where braid fanning is required, a discontinuity may exist at the interface of the cable braid and the connector body resulting in unwanted reflections of transmitted signal. Absent a discontinuity the radius of the outer conductor may change hence, the characteristic impedance would change. The characteristic impedance of a coaxial line is defined as:

wherein, Z is the characteristic impedance, b is the diameter of the outer conductor, a is the diameter of the inner conductor and E is the relative dielectric constant of the medium therebetween. An abrupt change in Z like a discontinuity results in wave reflection along a transmission line.

In contradisti'nction to the teachings and practices of the prior art we have designed a unique, reusable connector assembly having a self sealing feature and one that is substantially reflection free. 9

It is, accordingly, a general object of the instant invention to provide an improved connector assembly of the type described.

Another object of the instant invention is to provide a coaxial connector offering good radio frequency performance coupled with ease of assembly. 50

Another more specific object of the instant invention is to provide a coaxial radio frequency connector having excellent cable gripping properties.

Yet another object of the instant invention is to provide a coaxial cable connector wherein fanning of the cable braid is not necessary.

Still another more specific object of the instant invention is to provide a radio frequency coaxial cable connector providing impedance characteristics substantially equal to that of the cable. Y A still further, more specific object of the inst-ant invention is to provide animpedance transition device enabling substantially reflection free power transmission between coaxial cables of unequal physical dimensions.

Yet still another more specific object of the instant in- 65 Z0 log 3,209,287 Patented Sept. 28, 1965 ice vention is to provide a radio frequency coaxial cable connector which is reusable and which forms a natural water seal without a gasket.

The invention possesses other objects and features of advantage which, wit-h the foregoing, will become apparent to the reader in the following detailed description of the preferred form of the invention which is illustrated in the accompanying drawings as forming a part of the specification.

Referring to the drawings wherein like reference numerals denote like parts:

FIGURE 1 is a view, in cross section, of the left end of a completely assembled connector plug.

FIGURE 2 is a side view of a coaxial cable with some of the plug components mounted thereon, illustrating the manner of assembly.

FIGURE 3 is a side view of a coaxial cable with 'a completely assembled connector plug.

FIGURE 4 is an exploded view of the structure shown in FIGURE 1-.

FIGURE 5 is a side view of a preferred form of connector assembly comprising a plug and jack.

FIGURE 6 is a view in cross section of the plug illustrated in FIGURE 5.

FIGURE 7 is a view in cross section of the jack illustrated in FIGURE 5.

FIGURE 8 is an end View of the plug of FIGURE 6 looking. in the direction of arrows 88.

FIGURE 9 is an end view of the jack of FIGURE 7 looking in the direction of arrows 9-9.

FIGURE 10 is a sectional view of the connector elements providing impedance compensation.

Briefly stated, the foregoing objects and others, are accomplished by a unique design and cooperation of; a hollow externally threaded collar, a ferrule having a frusto-conical projection and a sleeve for engaging the collar. The ferrule, in addition to providing excellent electrical contact with the cable braid, provides clamping pressure to outer conductor and insulation of the cable between the ferrule and the inner surface of the threaded collar.

Referring to FIGURES 1 and 4, a coaxial cable 19 comprising; center conductor -23, dielectric 22, enter conductor (cable braid) 21 and rubber jacket 20 is shown. A hollow externally threaded collar '11 having an hexagonal flange is provided and adapted to frictionally engage jacket 20. Such engagement is effected by having the minimum diameter of collar 11 nearly equal to the outer diameter of cable 19. Collar 11 has successively increased internal diameter sections -1-1a, 11b and 11c along the body thereof.

Ferrule 13, having an annular flange 14 and a wedge shaped projection is adapted to be inserted between dielectric -22 and outer conductor 21.- The inner diameter of ferrule 13 is nearly equal to the external diameter of dielectric 22. An internally threaded sleeve 15, is provided to receive collar 11-. The wedge shaped portion of ferrule 13 cooperating with collar 11 and sleeve 15 is forced into a position whereby it applies radial pressure to braid 21 and rubber jacket This pressure is of sufficient magnitude to insure excellent engagement of cable 19. Likewise, this pressure forces jacket 20 into a confined volume and thereby creates a waterproof seal in addition to providing excellent radio frequency contact between the outer conductor 21 and ferrule 13.

The flat end of ferrule v13 abuts the shoulder 15b in sleeve 15 and insures proper positioning of ferrule "13 when the plug is assembled. Sleeve 15 has an opening, large enough to pass dielectric 22 and center conductor 23 into its tubular portion 15c enabling connection to contact pin 18.

After cable 19 is trimmed, collar '11 is slipped thereover. Next ferrule 13 is inserted between conductor 21 and dielectric 22. Contact pin 18 is passed over a bare projecting end of conductor 23 and soldered thereto. Following this, sleeve 15 is journaled onto the cable passing over ferrule 13. Collar 11 is brought into engagement therewith and the threaded portion 12 thereof is screwed into the body ofsleeve 15. A hexagonal head 15a, on sleeve 15, provides a gripping surface for tightening the connection between collar '11 and sleeve 15. Seat 15b urges ferrule 13 under braid 21, and into its proper position, as the connection between collar 11 and sleeve 15 is secured.

In securing collar 11 and sleeve 15, ferrule 13 is properly positioned. In this .position the transmission line experiences no discontinuity or change in radius because ferrule 13 is a conductor and its inner radius is equal to that of outer conductor 21. This pressure on jacket 20 provides Waterproofing, however, the internally stepped portions 11a, 11b and 110 of ferrule 11 enhance this characteristic in addition to providing eminently good cable gripping properties. Furthermore, the section 20a of jacket 20 is forced within the threads of sleeve 15 forming a gasket to prevent water leakage through the threaded region between sleeve 15 and collar 11.

A member 16, concentric with sleeve 15 and passing thereover, is shown in position in FIGURE 3. Member 16 is adapted for locking engagement with a jacket having a female contact pin 32 (see FIGURE 7) adapted to mate with contact pin 18.

Referring now to FIGURES and 6, the composite connector assembly including the complementary or right hand end thereof is shown. The right hand end of the connector assembly will hereinafter be referred to as the jack. In this embodiment the connector clamp structure is somewhat modified as will be described hereinbelow. Collar 11 and ferrule 13 are substantially identical to those previously illustrated and function in the same manner. On the other hand, sleeve is made up of two

separate parts

15d and 15e. This change in design was primarily for ease of manufacturing. In assembly, parts 15d and 1'5e are mated and stamped together. It is noted that member 15d has a circumferential seat therein adapted to accommodate an annular ridge on ferrule 13 of diameter nearly equal to the seat on member 15d. This arrangement insures proper alignment of ferrule 13.

Member 16 encircles a portion of sleeve 15d and defines a cavity therebetween. Positioned within said cavity is spring 26 which is arranged to urge member 16 to the left as far as it will go; in this particular case, to the point where member 16 abuts a hexagonal flange 15f. Guideway 24 on member 16 is provided for looking engagement with the jack having bayonet type locking fingers 31 projecting radially therefrom. In this particular embodiment three locking fingers 31 spaced 120 apart were used satisfactorily.

As will readily be understood from a reconsideration of Equation (1), a change in Z, should result from the changing diameter of the conductors caused by the connector assembly. More specifically, the addition of contact pin 18 to enter conductor 23 causes a discontinuity in the propagating transverse electric-magnetic mode (hereinafter referred to as TEM). If a constant diameter outer conductor is utilized, the equivalent circuit consists of two sections of different characteristic impedances coupled by a shunt capacitance due to the presence of transverse magnetic (hereinafter referred to as TM) modes at the point of discontinuity. Reflections are caused by the TM capacitance and the mismatch in characteristic impedances for the TEM mode. There are many ways to compensate for these possible reflections as is obvious to those skilled in this particular art. Whatever the method the ratio b/a must remain constant to avoid a change in Z Theoretically this condition is easily met, however, as a practical matter it is not. In this respect, we have found that a linear transition between equal ratios of the diameters satisfactorily eliminates power reflections.

Referring next to FIGURE 10 this linear transition will now be described. As previously noted Z will not vary if the factor b/a is constant. The coaxial cable has a specific Z which relates to the parameters of the cable and to b and a Assuming that dielectric 22 and inserts 27 and 33 have nearly the same E (see Equation 1), the only problem is to equate the aforementioned ratios. To this end we have found that to linearly increase the outer diameter from 12 to b and at the same time abruptly increase the inner diameter a to a at the midpoint of said linear increase, provides a satisfactory substantially reflection free transition. It is noted, of course, that the ratio b /a is numerically equal to b /a Furthermore, the abrupt change in al takes place at a distance L/2 which is defined as one half the horizontal distance L. A similar design is employed in the pack assembly of FIGURE 7 with dielectric insert 33 and functions in the same way.

Contact pins 18 and 32 provide the abrupt change from diameter a to ri This change takes place at the distance L/2 and the possibility of error is obviated 'because the recess in insert 27 terminates at the midpoint of its taper. Trimmed center conductor 23 passes through insert 27, but dielectric 22 abuts the Wall of said recess. Contact pin 18, having an external diameter a is aflixed to conductor 23 whereby it touches the end face of dielectric 22 at the midpoint L/ 2.

Insert 27 is secured in position in the connector body by means of crimping at 41 in FIGURE 6. Contact fingers 29 are secured to and spaced around the outer surface of dielectric 27 and provide frictional engagement with the inner surface of sleeve 30 of the. jack shown in FIGURE 7. Positioned within the cavity defined by member 16 the elastomer ring 28 which becomes compressed when the connector plug is in locking engagement with jack and provides a watertight seal therebetween.

Referring next to FIGURES 7 and 9 the jack assembly is shown. Female contact pin 32 is soldered to the center conductor 23 of another coaxial cable. Contact pin 32 is adapted to mate with contact pin 18. Dielectnic 33 is journaled into the cavity defiuied by sleeve 30 and is fixed therein by crimping at points 34. When the plug and jack are mated dielectric inserts 27 and 33 take the form of one continuous dielectric section.

Projecting from sleeve 30 are bayonet prongs 31 for locking engagement in guideways 24 of member 16. Sleeve 31 is both internally and externally threaded. The sleeves internal threads cooperate with collar 39 exactly as was done in the connector plug body with collar 11 and sleeve 15.

The jack body may be adapted for panel mounting and in that case sleeve 30 is provided with an outward radial flange 38. A rubber washer 37 seated in hexagonal flange 38 abuts the inner wall of said panel. Washer 36 and nut 35 are passed over the left end of the jack and engaged to the outer threads of sleeve 30 to secure the jack, which has been passed through an opening in the panel, to the equipment. By tightening nut 35, a watertight seal is created between the jack and the panel.

We have made radio frequency connector pairs in accordance with the teachings of the instant invention for 0.200 inch outer diameter coaxial line exhibiting a low voltage standing wave ratio of less than 1.32 for frequencies under 5,000 megacycles. Both plug and jack '5 were made from brass stock except :for spring fingers 29 and contact 32 which were made of beryllium copper. Both the connector plug and jack attached were approximately inch in length and when coupled together measured about 1.33 inches. The units were gold flashed over a silver plating on the order of 0.0002 inch.

Because of the special cable clamping technique in the design of the instant invention, a discontinuity free path from the cable to the plug body is achieved. In addition to a naturally formed water seal, the connector assembly has good gripping action and is reusable.

In one embodiment, the clamp withstood a static load of seventy pounds for over fifteen minutes and failed after more than one thousand, ninety degree flexures with a five pound load. The failure noted in the iiexure test was not in the connector gripping area, but due to .a severance of the outer braid at the rear of collar 11.

From the foregoing, it is noted that we have provided a connector having good radio frequency performance, ease of assembly and with excellent cable gripping properties which represents a considerable advance over the prior art.

-It will be understood that the invention can be prac ticed otherwise than has been specifically described and is limited only by the scope of the appended claims. For example, the connector may be utilized to secure other terms of current carrying elements. Also, the connector may be used for splicing cables together as well as connection to panel mountings.

I claim:

1. An impedance matching device between coaxial lines of different physical dimensions having substantially equal impedances, comprising in combination: a coaxial line having a center and outer conductor wherein the outer diameter of said center conductor is a and the inner diameter of said outer conductor is b another coaxial line having a center conductor and an outer conductor wherein the outer diameter of said center conductor is and the inner diameter of said outer con- .ductor is b coaxial wave conducting means interposed between and connected to the outer conductors of said lines, respectively, having a linear taper from diameter b to diameter 12 and second wave conducting means connected to the center conductors of said lines, respectively, causing an abrupt transition from diameter 0 to diameter a wherein said abrupt transition occurs substantially at the midpoint of said taper along the axis thereof and is spaced therefrom.

2. In the device of claim 1 wherein: the ratio of b to a is equal to the ratio of b to 0 3. In the device of claim 2 wherein: a dielectric having a relative dielectric constant substantially equal to that of a dielectric used in said lines, fills the space between said first and second wave conducting means.

4. A coaxial impedance matching device for coupling between coaxial lines of unequal physical dimensions having substantially equal impedances comprising in combination: hollow conductive means interposed be tween and connected to outer conductors of said lines and having a frusto-conical surface; and a second conductive means connected to the center conductors of said lines and having an external diameter equal to the external diameter of the center conductor of the larger of the coaxial lines, said second conductive means extending from about the midpoint of said conical section to the larger of said center conductors along the axis thereot and spaced therefrom.

5. An impedance matching device between coaxial lines of ditferent physical dimensions having substantially equal impedances comprising in combination: a coaxial line having a center and outer conductor wherein the outer diameter of said center conductor is a and the inner diameter of said outer conductor is [2 another coaxial line having a center conductor and an outer conductor wherein the outer diameter of said center conductor is '6 and the inner diameter of said outer conductor is b coaxial wave-conducting means interposed between and connected to the outer conductors of said lines, respective ly, having a linear taper from diameter b to diameter b and second wave-conducting means connected to the center conductors of said lines, respectively, said second waveconducting means including a portion thereof having a diameter substantially equal to a and disposed coaxially with that portion of said coaxial wave-conducting 'meansextendingfrom-said outer conductor having an inner diameter of b and a second portion thereof having a diameter substantially equal to a and disposed coaxially with that portion of said coaxial wave-conducting means extending from said outer conductor having an inner diameter of b said portion and said second portion being joined in an abrupt transition from diameter a to diameter a whereby the impedance of said impedance matching device is substantially equal to the impedance of said coaxial lines.

6. An electrical connector adapted for use with a multiconductor cable, said cable having a center and an outer conductor wherein the outer diameter of said center conductor is a and the inner diameter of said outer conductor is b said connector comprising: a conductive connector sleeve having a clamp portion adapted to conductively engage said outer conductor, a second portion with an inner diameter b and a coaxial wave-conducting portion therebetween having a linearly tapered inner surface varying from a diameter b at said clamp portion to a diameter b at said second portion; inner conductor means having a first portion of diameter a extending from said second conductor into said wave-conducting portion and a second portion of diameter a coaxial and coextensive with the second portion of said sleeve and extending into said coaxial wave-conducting portion, said first and second portions of said inner conductor means being joined together in an abrupt transistion from diameter a to diameter a and the ration a /b being equal to the ration a /b whereby the impedance of said electrical connector is substantially equal to the impedance of said cable; and dielectric means disposed between said connector sleeve and said inner conductor means.

7. An electrical connector adapted for use with a multiconductor cable, said cable having a center and an outer conductor wherein the outer diameter of said center conductor is a and the inner diameter of said outer conductor is b said connector comprising: a conductive connector sleeve having a clamp portion adapted to conductively engage said outer conductor, a second portion with an inner diameter b and a coaxial wave-conducting portion therebetween having a tapered inner surface varying from a diameter b at said clamp portion to a diameter 11 at said second portion; inner conductor means including a pin having a diameter a and extending into said tapered coaxial wave-conducting portion to substantially the midpoint thereof, said pin being adapted for securement to said center conductor; and dielectric means disposed between said connector sleeve and said inner conductor means.

8. An electrical connector adapted for use with a multiconductor cable, said cable having a center and an outer conductor wherein the outer diameter of said center conductor is a and the inner diameter of said outer conductor is b said connector comprising: a conductive connect-or sleeve having a clamp portion to conductively engage said outer conductor, a second portion with an inner diameter b and a coaxial wave-conducting portion therebetween having a tapered inner surface varying from a diameter b; at said clamp portion to a diameter b at said second portion; inner conductor means including a pin having a diameter a and extending into said tapered coaxial wave-conducting portion to an intermediate point thereof, said intermediate point being at above the midpoint of said tapered coaxial wave-conducting portion whereby the impedance of said electrical conmulticonductor cable; and dielectric means disposed be- 'tween said connector sleeve and said inner coEluctor means. 0

References Cited by the Examiner UNITED STATES PATENTS 1,326,250 12/19 Brown et a1. 285-246 1,841,473

1/32 Green l7488 8 Violette 33334 Wetherill 174 89 X Wheeler. Melcher 339177 Kaiser 285-251 X Valach l7487 DARRELL L. CLAY, Acting Primary Examiner.

E. JAMES SAX, JOHN P. WILDMAN, JOHN F.

BURNS, Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. $r,209,287 September 28 1965 Edwin S; Qxner It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 35 for "jacket" read jack line 69, for "enter" read center column 4, line 27, for "pack" read jack line 52 for "definied" read defined column 6,

lines

38 and 39, for "ration", each occurrence, read ratio line 73, for "above" read about Signed and sealed this 10th day of May 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER A sting Officer Commissioner of Patents

Claims

4. A COAXIAL IMPEDANCE MATCHING DEVICE FOR COUPLING BETWEEN COAXIAL LINES OF UNEQUAL PHYSICAL DIMENSIONS HAVING SUBSTANTIALLY EQUAL IMPEDANCES COMPRISING IN COMBINATION: HOLLOW CONDUCTIVE MEANS INTERPOSED BETWEEN AND CONNECTED TO OUTER CONDUCTORS OF SAID LINES AND HAVING A FRUSTO-CONICAL SURFACE; AND A SECOND CONDUCTIVE MEANS CONNECTED TO THE CENTER CONDUCTORS OF SAID LINES AND HAVING AN EXTERNAL DIAMETER EQUAL TO THE EXTERNAL DIAMETER OF THE CENTER CONDUCTOR OF THE LARGER OF THE COAXIAL LINES, SAID SECOND CONDUCTIVE MEANS EXTENDING FROM ABOUT THE MIDPOINT OF SAID CONICAL SECTION TO THE LARGER OF SAID CENTER CONDUCTORS ALONG THE AXIS THEREOF AND SPACED THEREFORM.