US2644028A

US2644028A - Expansion joint for coaxial lines

Info

Publication number: US2644028A
Application number: US441731A
Authority: US
Inventors: Edwin J Bernet
Original assignee: Individual
Current assignee: Individual
Priority date: 1942-05-04
Filing date: 1942-05-04
Publication date: 1953-06-30
Anticipated expiration: 1970-06-30

Description

June 30, 1953 E. J. BERNET 2,644,028

EXPANSION JOINT FOR COAXIAL'LINES Filed May 4, 1942 gvwam bow Edwin J Bernet a, y l m and mast.

j resonant transmission lines.

Patented June 30, 1953 EXPANSION JOINT FOR COAXIAL LINES Edwin J. Bernet, Washington, D. 0.

Application May 4, 1942, Serial No. 441,731

4 Claims. (-01. 174-88) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates broadly to expansion joints and more specifically to such joints for use in coaxial transmission lines, such as those used in connection with transceiver antennas.

It is well known that dissimilar substances,

.such as wood and metals, when subjected to variations in temperature will expand or contract by different amounts.

There has long existed a need of a device for coaxial transmission lines, secured to a ships mast or the like, that will compensate for differentia1 changes in length of said transmission line Many difficulties have been encountered in attempting to solve this problem. The

' principal difficulty lies in keeping the characteristic impedance of the line constant, or nearly so.

Many devices have been developed to compensate for changes in length of a coaxial transmission line due to changes in temperature, but they have also altered the characteristic impedance of the line, thereby setting up standing waves on the line, and resulting in a considerable amount of reflection. This is an undesirable effect in non- Though my invention does not'completely eliminate this effect it I greatly improves its condition.

An object of this invention is to compensate for the changes in length of a coaxial transmission line, due to wind or other extraneous forces which would produce a relative mechanical movement between the line itself and its support.

A more specific object of this invention is to compensate for the changes in length of a coaxial my invention;

Fig. 2 is a side View of one section of the transmission line or splicing section;

Fig. 3 is an end View of the section of transmission line or splicing section, shown in Fig. 2;

Fig. 4 is an elevational View in cross-section of the expansion joint of Fig. 1, in a contracted state, and

Fig. 5 illustrates, in cross-section, an alternate arrangement of parts constituting a second embodiment of the invention.

It is Well known to those skilled in the art that a change in characteristic impedance of a nonresonant coaxial line will produce reflection. a coaxial line the characteristic impedance is determined by the ratio between the inside diameter D1, of the outer conductor to the outside diameter D2, of the inner conductor.

when air is the dielectric. It is therefore obvious that this ratio should be kept as nearly constant as possible at all points along the line for best results in energy transmission. The invention succeeds in accomplishing this result to a greater extent than has before been realized.

' In accordance with the invention the coaxial transmission line is provided, at any convenient point along its length with a splicing section as shown at B in Fig. 1, comprising a pair of coaxial sleeves 3 and 3. The splicing section is shown as inserted between two sections A and A of the transmission line, the conductors of section A being marked I and 5 and those of section A being marked 2 and T. In Fig. l the sleeves of the splicing section are shown telescoped outside the respective conductors of the line sections over which they have a snug fit. One end of each of the sleeves is welded to its respective line conductor as shown at 5, while the ends of the conductors of the other section of the line are slotted as shown at 9 in Fig. 2 to provide a plurality of fingers l0 which spring outwardly to provide a constant electrical contact between line section A and splicing section B regardless of the relative movement of the sleeve and conductor. In Fig. 1 splicing sleeve section B has a zero setting,

. namely, the ratio of diameters throughout the line and splicing section remain unchanged.

Inner conductors l, 2 are extended a selected distance beyond the ends of outer conductors 6, l

of main line A-A". Inner conductor 2 is extended beyond the end of outer conductor 7 a dispurposes.

The length of outer sleeve 4 of splicing section B is equal to the distance between the adjacent ends of

outer conductors

5 and 1 plus a distance required for a suitable weld on 1 and the distance needed for coupling and change in length purposes. The length of inner sleeve 3 of splicing section B is equal to the distance between the adjacent ends of the outer conductors ii and 1.

The thickness of inner sleeve 3 is selected equal to an amount required to keep the ratio of diameters constant for a zero setting of the splicing section. The inside diameter of outer sleeve l is equal to D1 plus twice the thickness of outer conductors t or 'i and the outside diameter of inner sleeve 3 is equal to D2 l twice the thickness of inner sleeve 3. Therefore the thickness of sleeve 3 is selected to maintain the ratio constant.

From the foregoing description it is obvious that a zero setting may only be realized when the respective ends of inner sleeve and outer conductors ii, i lie in the same plane perpendicular to the longitudinal axis of the line section A A.

For best overall performance of the syst m, splicing section B should have a zero setting for the average temperature to which the line will be exposed.

The splicing sleeves 3, l ma r be positioned on the inside surfaces of their respective conductors i, ii and 2, l as shown by the embodiment illustrated in Fig. 5. Outer conductors t, l protrude beyond the ends of inner conductors i, 2. Fhe length of outer sleeve i is chosen equal to the distance between adjacent ends of inner conductor l, 2 at the splicing section B. The length of inner sleeve is chosen in a way similar to that described for choosing the outer sleeve of the previous system. This system will give results which equal that of the system previously ole-- scribed but due to the difficulties in machining sleeves 4'. to the desired thickness, the previous system is preferred.

The graduated scale 3 simplifies the positioning of said splicing section to a zero setting.

If, as shown in Fig. 1, the sleeves i are positioned on the outside surfaces of conductors i, 2 and 6, l, fingers ill are formed in outer conductor 6 and inner conductor l. The graduated scale is located on the outside surface of conductor ii as shown by Fig. 2.

If, as shown in Fig. 5, sleeves 3, ii are positioned on the inside surfaces of conductors I, 2 and 6, l, fingers l are cut in outer sleeve i and inner sleeve 3. The graduated scale 8 is now located on the outside surface of sleeve l.

When a drop in temperature occurs the line and splicing section will appear something like that shown by the cross-sectional view of Fig. i.

The ends of outer conductor 6 and inner sleeve 3 no longer lie in the same plane perpendicular to the longitudinal axis of a line section AA. A small physical discontinuity will now exist in the splicing section B. The ratio of diameters has changed to D1 plus twice the thickness of conductor 6 to D2. A small percentage of reflection Will ensue. However, due to the inherent rodeo- 1 tion, principally caused by insulators, the reflection due to physical discontinuity will be almost negligible.

In comparative tests my method of length compensation has produced from 2- l% reflection for a line length of 100 ft. and a temperature range of 0-120 C., while other methods have produced from 2060% reflection under the same condi tions.

Normally in practice there are many incidental features employed in the construction of a splicing section of this type, but they do not form part of my invention. A tubular bellows is commonly placed over part of the coaxial surface of line A and splicing section B to protect said line surface from oxidizing and insures good electrical contact. Normally a gas seal is provided around the edge of outer conductor d to prevent gas from escaping out of the coaxial line and inflating the bellows. Often a ring stop is provided on the surface of conductor 6 to prevent splicing member B from being wedged down too deep onto coaxial line section A.

Although I have shown and described certain and specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

The invention described herein may bemanufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. Means for compensating for changes in the length of a coaxial non-resonant transmission line, due to changes of temperature, comprising a pair of similar, coaxially aligned transmission line sections and means for joining the adjacent ends of said sections, the adjacent ends of the inner conductors of said sections protruding beyond the ends of the outer conductors of their respective sections, said joining means comprising an inner cylindrical sleeve snugly fitted over said adjacent ends of said inner conductor, and an outer cylindrical sleeve snugly fitted over adjacent ends of said outer conductor, one end of each of said sleeves being immovably and conductively secured to its respective conductor, the other end of each of said sleeves being in sliding electrical contact with its respective conductor, the length and positioning of said inner sleeve being such that at a predetermined reference temperature in the normal service temperature range of said line, each end of said inner sleeve will lie in the same transverse plane as each one of said adjacent ends of said outer conductor, the ratio between the inside diameter of said outer sleeve and the outside diameter of said inner sleeve being the same as the ratio between the corresponding diameters of said conductors.

2. Means for compensating for changes in length of a coaxial non-resonant transmission line, due to changes in temperature, comprising a pair of similar, coaxially aligned transmission line sections and means for joining adjacent ends of said sections, the adjacent ends of the outer conductors of said sections protruding beyond the ends of the inner conductors of their respective sections, said joining means comprising an inner cylindrical sleeve snugly fitting in said adj acent ends of said inner conductor, and an outer cylindrical sleeve snugly fitting in said adjacent ends of said outer conductor, one end of each of said sleeves being immovably and conduotively secured to its respective conductor, the other end of each of said sleeves being in sliding electrical contact with its respective conductor, the length and positioning of said outer sleeve being such that at a predetermined reference temperature in the normal service range of said line, each end of said outer sleeve lies in the same transverse plane as each of said adjacent ends of said inner conductor, the ratio between the inside diameter of said outer sleeve and outside diameter of said inner sleeve being the same as the ratio between the corresponding diameters of said conductors.

3. Means for compensating for changes in length of a coaxial non-resonant transmission line, due to changes in temperature, comprising a pair of similar, coaxially aligned transmission line sections, and means for joining adjacent ends of said sections, the ends of one conductor of each of said sections protruding beyond the ends of the other conductor of their respective sections, said joining means comprising an inner cylindrical sleeve snugly telescoping the adjacent ends of the inner conductor of said sections and an outer cylindrical sleeve snugly telescoping the adjacent ends of the outer conductor of said sections, one end of each of said sleeves being immovably and conductively secured to its respective conductor, the other end of each of said sleeves being in sliding electrical contact with its respective conductor, the length and positioning of one of said sleeves being such that at a predetermined reference temperature in the normal service temperature range of said line, each end of said one of said sleeves will be in the same transverse plane as each one of the adjacent ends of one of said conductors, the ratio between the inside diameter of said outer sleeve and the outside diameter of said inner sleeve being the same as the ratio between the corresponding diameters of said conductors.

4. Means for compensating for changes in length of a coaxial non-resonant transmission line, due to changes in temperature, comprising a pair of similar transmission line sections having similar characteristic impedances, and means for joining adjacent ends of said sections, the adjacent ends of one conductor of said sections protruding beyond the adjacent ends of the other conductor of said sections, said joining means comprising an inner cylindrical sleeve snugly telescoping the adjacent ends of the inner conductor of said sections, and an outer cylindrical sleeve snugly telescoping the adjacent ends of the outer conductor of said sections, one end of each of said sleeves being immovably and conductively secured to its respective conductor, the other end of each of said sleeves being in sliding electrical contact with its respective conductor, the length and positionin of one of said sleeves being such that at a predetermined reference temperature in the normal service temperature range of said line, each end of said one of said sleeves will b in the same transverse plane as each one of the adjacent ends of one of said conductors, and means provided for accurately positioning said sleeves at the reference temperature, the ratio between the inside diameter of said outer sleeve and the outside diameter of said inner sleeve being the same as the ratio between the corresponding diameters of said conductors.

EDWIN J. BERNET.

References Cited in the me of this patent UNITED STATES PATENTS Number Name Date 1,037,522 Pindtershoien Sept. 3, 1912 1,841,473 Green Jan. 19, 1932 1,921,117 Darbord Aug. 8, 1933 1,929,878 Clavier Oct. 10, 1933 1,937,652 Green Dec. 5, 1933 2,044,580 Leach June 16, 1936 2,165,961 Cork et a1 July 11, 1939 2,249,443 Tringham July 15, 1941 2,404,797 Hansen July 30, 1946 2,427,752 Strempel et a1 Sept. 23, 1947 2,437,067 Bingley Mar. 2', 1948 FOREIGN PATENTS Number Country Date 17,402 Great Britain of 1890