US3087129A

US3087129A - Centerless coaxial connector

Info

Publication number: US3087129A
Application number: US11114A
Authority: US
Inventors: Mario A Maury; Henry K Omiya
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-02-25
Filing date: 1960-02-25
Publication date: 1963-04-23
Anticipated expiration: 1980-04-23

Description

April 23, 1963A M. A. MAURY ETAI. 3,087,129

cENTERLEss coAxIAL CONNECTOR Filed Feb. 25, 1960 INVENToRs Mar/'o A. Maury /a /0/ 2/ /9 Henry K. Om/ya ATTORNEYS Unite 3,087,129 CENTERLESS COAXIAL CNNECTOR Mario A. Maury, Montclair, and Henry K. Omiya, Fullerton, Calif., assigncrs, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Feb. 25, 1960, Ser. No. 11,1% 6 Claims. (Cl. 333-9) The present invention relates to coaxial cables and more particularly to new and improved end terminations for such coaxial cables capable of forming wide band centerless coaxial connectors.

For a number of years in the field of microwave transmission, it has been the general practice to employ coaxial cables for the conduction of radio frequency energy. In missile work, as well as other physically demanding electronic applications, it is frequently necessary to couple radio frequency energy from a first coaxial transmission line to a second coaxial transmission line in the form of a quick disconnect. The latter expedient for coupling coaxial cables must possess characteristics of extreme ruggedness, if it is to withstand the very high orders of vibration, temperature and shock commonly encountered in missiles and related devices.

Before the introduction of the coupling device of the V present invention, the prior art coupling expedients made use of mechanical contact fingers for coupling the conductors of one coaxial cable to those of an adjacent cable. However, such contact fingers have always had the rather stringent requirement that the connectors be accurately `aligned if the contact fingers were -to be properly seated, as they must for proper performance. This last requisite imposes an extreme design problem since lmanufacturing tolerances for connectors utilizing such contact fingers must be kept within highly prohibitive figures, making the practicality of such a coupling expedient questionable. It can be readily visualized that the use of such contact fingers for coupling microwave transmission lines under extreme environmental conditions, where accurate alignment would be difficult, if not impossible, presents ia serious problem. Those concerned with the development of coaxial connectors have long recognized the need for a quick disconnect device obviating the use of such ltroublesome contact fingers and the present invention clearly fulfills this need.

The general purpose of this invention is to provide a coaxial connector which embraces substantially all of the advantages of similarly employed coaxial connectors and possesses none of the aforedescribed disadvantages. To attain this, the present invention contemplates a unique end termination for coaxial cables obviating the use of contact fingers by providing for a transition in mode of transmission at the point of coupling so that the center conductors of the coaxial lines need not extend through the connector. The result is a ruggedized wide frequency band centerless coaxial connector having improved resistance to high orders of vibration, temperature and shock. The device of the instant invention simultaneously obviates the requirement of accurate cable alignment during coupling, thereby enabling considerable reduction of the usually required high order of manufacturing tolerances.

The principal or predominant mode of transmission of a coaxial cable is generally known `as the TEM mode and an electromagnetic wave of any frequency may be transmitted in this mode. `It is also possible on such coaxial transmission lines to generate higher order modes which do not eliminate the center conductor of the coaxial cable but do approach the characteristics of a circular wave guide as the diameter of the center conductor approaches zero. Such higher order modes (TEM, TE21, T1531, TEM, TMll, etc.) have not been generally acceptable because of the coupling difficulties encountered when using such modes and the further disadvantage in that they require the use of complex mode suppressor filters which cornplicate the design of standard transmission lines as well as introduce inherent losses into the line. There is, however, a mode known in circular wave guide theory as the TMm mode which is very similar to the TEM mode of the coaxial cable. The device of the instant invention seizes upon this similarity of the TMm mode to eliminate the center conductor of the coaxial cable at the coupling point. The resulting structure is considerably simpler than previously utilized in coupling devices, resolving itself into a mode transitional element of very wide operational frequency characteristics.

Thus, it will be `apparent that one object of the present invention is the provision of a connector for coaxial cables which obviates the need for center conductor contact fingers.

Another object is to provide a centerless coaxial connector which may be rapidly utilized to connect two sections of coaxial cable together without the requirement of critical alignment, thus providing a quick disconnect device.

A further object of the invention resides in the provision of a centerless coaxial cable which is extremely rugged and has a -high resistance to vibration, temperature and shock.

Still another object is to provide a centerless coaxial connector incorporated as an end termination on the coaxial cable itself and which does not have the center conductor of the coaxial cable extending through said connecting end termination portion.

Yet yanother object of the present invention is the provision of a centerless coaxial cable connector which transforms the TEM mode of the coaxial cable to the TMm mode of Ia circular wave guide at the point of coupling,

A still further object of the present invention is to provide a novel coaxial cable embodying a connector having all of the aforementioned features as an end termination integrally formed with the cable itself.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the sa-me becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is an axial section through a coaxial transmission line showing a graphical representation of the TEM mode of a coaxial cable;

FIG. 2 is an axial section through the centerless coaxial connector of the instant invention showing a graphical representation of the TMm mode of a circular wave guide;

FIG. 3 is a longitudinal section through a pair of mating coaxial cables each embodying a centerless end termination in accordance with the instant invention;

FIG. 4 is a longitudinal section through a pair of coaxial cables coupled together by means of the centerless coaxial connecting expedient of the instant invention and wherein the two cables are held in butt joint relation by means of a threaded retaining ring;

FIG. 5 is a longitudinal section of a pair of coaxial cables embodying the centerless coaxial connecting expedient of the instant invention and utilizing a simple choke connection to hold the cables together; and

FIG. 6 is an exploded view in perspective of the cable arrangement shown in FIG. 5.

Referring now to the drawings, wherein like reference characters denote like or corresponding parts throughout the drawings, there is shown in FIG. 1 a graphical representation of the TEM mode of a coaxial transmission line, the latter mode being the principal or predominant mode transmitted by such a line. It will be noted from FIG. 1 that the TEM mode requires the presence of both an outer cylindrical conductor and an inner coaxial conductor. The graphical representation of FIG. 2, on the other hand, shows that the TMm mode of a circular wave guide can be sustained without the presence of a center conductor. The instant invention takes advantage of the latter simplicity of structure capable of sustaining the TMUl mode to provide a unique coupling expedient between a pair of coaxial cables.

It will be observed that it is necessary to effect an efcient transition from the TEM mode to the TMm mode. Referring now to FIG. 3 of the drawings, the latter transition can easily be accomplished by the use of a probe 12 placed longitudinally and coaxially with the center conductor 14 of a coaxial cable, such as the cable 10, to be coupled. Such a probe 12, preferably, is merely an extension of the center conductor 14 itself, rather than consisting of a separate conducting element attached to the latter center conductor. A coupling expedient is thereby provided for inter-connecting adjacent ends of any two coaxial conductor ultra high frequency energy transmission lines, which may or may not be flexible.

Each transmission line, except for the end termination connecting portion, is of conventional construction comprising a exible solid wire

inner conductor

14 or 15, a

continuous insulator sleeve

16 or 17 of a dielectric material which is suitably flexible and has sutiiciently high dielectric properties for the use desired, an outer conductor 18 or v19 which is typically of braided copper to permit desired expansibility and flexibility, and an external electrically insulating covering (not shown) of a suitable material, such as rubber or saturated fabric. The end termination centerless connecting

portions

20 and 21 of the coaxial cables and 11 are filled with a second dielectric material 23, which may or may not be the same material as the dielectric material utilized in the remaining portions of the cables 10' and 11, as will be hereinafter described in detail. The extension of the

center conductors

14 and 15 of cables 10 and 11 as probes 12 and l13 imbedded in the dielectric material 23 of the connecting end terminationseifectively transforms the TEM mode of the cable into a TMol circular wave guide mode in the end termination connecting portion. Ihe latter TMm mode is propagated through the end termination connecting portion 20 of the first cable 110 and then through the end termination connecting portion Z1 of a second cable `.111, the centerless coaxial connector of which is butted against the connector of the first cable 10. Once having been propagated through the connecting portion 21 of the second cable 11 the TMm mode is reconverted in the second cable to the original TEM mode of the first coaxial cable.

FIG. 4 shows two coaxial cables embodying the coupling expedient of the instant invention and held together by means of a cylindrical threaded retaining ring 24 which is used to clamp the two cable end portion connectors 20 and 2.1 together in butt-joint relation. As is clearly evident from FIG. 4, the accuracy of alignment of the two

cable end portions

20 and 21 is not critical since no Contact nger probes are required in connecting the latter end portions together.

FIGS. 5 and 6 show a further embodiment of the invention utilizing the same type of centerless coaxial connecting portions shown in FIGS. 3 and 4 but using a choke joint connector 25 to hold the two coaxial cable end portions in butt-joint relation by means of a friction squeeze t. 'Ihe latter embodiment is especially suitable for quick disconnect applications.

In dealing with centerless coaxial connectors of the circular wave guide type, as contemplated by the instant invention, one objection immediately becomes apparent due to the cut-off frequency characteristics exhibited by such wave guide structures. That is, the proposed centerless coaxial connectors would be frequency sensitive. Another objection would appear to lie in the bulkiness of such a structure. For example, the diameter of an airilled circular X-band wave guide would have to be 1.38 inches if it were to be able to effectively propagate the TMm mode near the cut-olf frequency of y6.57 kmc. The latter figures may be readily calculated by utilizing the descriptive theoretical information and equations set forth on pages 135 through 146 of Electronic and Radio Engineering, by Frederick Emmons Terman, McGraw- Hill Book Company, Inc., New York, 1955, 4th edition, as follows:

where For the TMm mode in a circular waveguide,

Equation l therefore becomes Solving for r, the radius of the waveguide,

The diameter of the circular waveguide in inches is thus Ac=2.6lr= =4.57 cm. (3)

or 1.38 inches, as stated.

From the above, it readily follows that in using the proper dielectric constant `for the material `filling the waveguide structure, the diameter of the waveguide can be reduced to any convenient size, as for example, the same size as the remaining portion 0f the coaxial cable for which it serves as an end termination. In such a case, the outer wall of the circular waveguide would merely be a continuation of the outer cylindrical conductor for the remainder of the coaxial cable. In the above example, let us say that the diameter of the circular waveguide is not to exceed 0.280 inch or 0.710 cm. (r=0.355 cm.).

From Equation 4,

where Nc=cutol wavelength of the waveguide in the presence of the new dielectric filling material.

The following relation also exists:

where e=dielectric constant of the material iilling the circular waveguide.

Solving Equation 7 for e,

)Je 2 4,6 8) Substituting the values of Nc and Ac yfor the instant problem,

Hence the dielectric requirements for any particular diameter end termination coaxial connector and for any desired cut-off frequency may be readily determined by the above method of computation. Many materials having suitably high dielectric constants for such purposes have recently become available in the form of ceramics. Continuing research and subsequent development of improved dielectrics offering an even Wider range of available dielectric constants will further increase the applicability of the centerless coaxial connector of the instant invention.

The resulting devices shown in FIGS. 4, 5 and 6 exhibit extremely rugged properties including very high resistance to vibration, temperature and shock. Nor is great accuracy of alignment required in coupling any two cables embodying the instant invention since no troublesome contact fingers are involved. It is believed that the proposed centerless coaxial connector of the instant invention directly incorporated as an end termination into a coaxial cable, is an item that provides a substantial advance in the coaxial connector art.

Obviously many modifications and variations of the present invention are possible in 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.

Having thus described the invention, what is claimed is:

1. In a system for the transmission of radio frequency energy, a pair of coaxial cables, each of said cables having inner and outer coaxial electrical conductors separated by a first and -a second dielectric material, and an end structure on each of said cables including a circular cylindrical outer conductor extending a predetermined distance beyond said first dielectric material `and filled with said second dielectric material, the inner conductor of each of said coaxial cables extending only partly into and sealed within the second dielectric material of its respective cable end structure, the outer conductors of said end structures being integral with the outer conductors of their respective coaxial cables, and means including -a member adjustably mounted on one end structure and snugly engaging the other end structure for clamping the said end structures of each of said cables and the second dielectric material therein in butt-joint relation.

2. A centerless connecting end termination for a coaxial cable having inner and outer coaxial electrical conductors separated by la first dielectric composed of a flexible material and a second dielectric composed of a different material than the first dielectric, said end termination comprising a circular cylindrical outer conductor extending beyond said first dielectric and filled with said second dielectric material, the inner conductor of said coaxial cable extending only partly into the second dielectric material of said end termination and embedded therein, and the outer conductor of said end termination being integral with the outer conductor of said cable.

3. In a system for the transmission of radio frequency energy, a coaxial cable having inner and outer coaxial electrical conductors, a first dielectric composed of a flexible material and electrically insulating said conductors from each other, and an end structure consisting of an integral extension of said outer electrical conductor of said coaxial cable filled with a second dielectric cornposed of a substantially solid material, the inner conductor of said coaxial cable having a probe thereon and embedded in said second dielectric material short of the terminal end of the extension on the outer conductor.

4. In a system for the transmission of radio frequency energy, a plurality of coaxial cables, each having outer and inner coaxial electrical conductors separated by dielectric material, connected one to another at their respective ends by means of an end structure on each of said cables, said cable end structures each consisting of an outer electrically conductive sleeve filled entirely with dielectric material, the dielectric material of the end structures differing from the dielectric material in the remaining portion of the coaxial cable and means on the end structure of each cable for maintaining the end structure and the dielectric material therein in butt-joint relation on one end structure and a retaining ring threaded on the other end structure in clamping engagement with the flange.

5. 'In a system for the transmission of radio frequency energy, first means for conducting said radio frequency energy in the TEM mode, second means for conducting said radio frequency energy in the TEM mode, said first and second means including coaxial cables each having outer and inner coaxial electrical conductors and a dielectric of solid material electrically insulating said conductors from each other, said inner conductor terminating short of the terminal end of the outer conductor and having `a probe embedded in the dielectric material, and third means carried by the outer conductor of one cable, complementary means carried by the outer conductor of the other cable in engagement with the means on said one cable, for coupling and maintaining said rst and second means together in abutting relationship, the predominant mode of transmission of said third means being a mode other than the TEM mode.

6. In a system for the transmission of radio frequency energy, first means for conducting said radio frequency energy in the TEM mode, second means for conducting said radio frequency energy in the TEM mode, said first and second means including a pair of coaxial cables having outer and inner coaxial electrical conductors and a dielectric of solid material electrically insulting said conductors for each other, said inner conductors terminating short of the terminal ends of outer conductors and having a probe imbedded in the dielectric material, and third means inserted between said first and second means for coupling said first and second means together, said third means including -a circular waveguide structure having an outer cylindrical conductive sleeve on the terminal end of the conductor of one cable and overlapping the terminal end of the outer conductor of the other cable and in spaced relationship thereto and filled with the dielectri material, the predominan-t mode of transmission of said third means being the TMm mode.

References Cited in the file of this patent UNITED STATES PATENTS 2,527,146 Mumford Oct. 24, 1950' 2,683,251 Ramo July 6, 1954 2,746,018 Sichak May 15, 1956 2,929,034 Doherty Mar. l5, 1960

Claims

2. A CENTERLESS CONNECTING END TERMINATION FOR A COAXIAL CABLE HAVING INNER AND OUTER COAXIAL ELECTRICAL CONDUCTORS SEPARATED BY A FIRST DIELECTRIC COMPOSED OF A FLEXIBLE MATERIAL AND A SECOND DIELECTRIC COMPOSED OF A DIFFERENT MATERIAL THAN THE FIRST DIELECTRIC, SAID END TERMINATION COMPRISING A CIRCULAR CYLINDRICAL OUTER CONDUCTOR EXTENDING BEYOND SAID FIRST DIELECTRIC AND FILLED WITH SAID SECOND DIELECTRIC MATERIAL, THE INNER CONDUCTOR OF SAID COAXIAL CABLE EXTENDING ONLY PARTLY INTO THE SECOND DIELECTRIC MATERIAL OF SAID END TERMINATION AND EMBEDDED THEREIN, AND THE OUTER CONDUCTOR OF SAID END TERMINATION BEING INTEGRAL WITH THE OUTER CONDUCTOR OF SAID CABLE.