US2678428A - Coaxial transmission line termination - Google Patents

Description

May 11, 1954 o. o. FlET 2,678,428

COAXIAL TRANSMISSION LINE TERMINATION Filed Sept. 7, 1949 15 In "1 I 23 lNVENTOF} Owen 0.1 161 BY f I ATTORNEY Patented May 11, 1954 R ISSION L NE. TERMINATION Q cn O an o Fiet, O yn, N. J., assignor to Radi Corporation f me ica, a c rporati n of D laware Application Septemb I, 1949, Serial. 114,400

6 Claims- 1 The invention relates to coaxial transmission lines and it particularly pertains to an improved arrangement for terminating open-ended coaxial transmission line sections.

Open-ended coaxial transmission lines are very frequently employed in high frequency radio in stailations asimpedance matching devices, r650! nant circuit elements, notch filters, and the like,to great advantage. While theoretically the known arrangements are equally applicable to high gr power installations as well as low power installations. it has been found. that in installations of 10 kw. and higher ower, the differential thermal expansion between the inner and outer conductors of an open-ended coaxial transmission line has a detrimental effect .on the tuning of the line.

It. is: an object of the invention to provide a terminating arrangement for an open-ended coaxial transmission line which-willnot be affected by temperature variations.

It. is another object of the invention to provide a termination for an open-ended coaxial transmission line eliminating the deleterious effects caused by differential thermal expansion between the inner and outer conductors of the. line.

it is a further object of the inventionto provide a simple and inexpensive termination for a coaxial transmission line which is readily j-111st able and completely reliable in. operation.

These and other obi ects of the invention which appear as. the specification pro esse are attained by means of a device consisting essendollar of. a con uctive sleeve placed over the en of the r conductor of an open-ended coaxi l trshsm ion line, which sleeve i rest in y the outer conductor on ,.an mea s. e p v d to maintain elec ric l con act between he i n conduct and the sleeve, m anwhile permit ing he inner conduc o to move within e l e accordance i h temper u e variations whereby the effect of differential thermal expansion between the inner and outer conductors is elim n t The inv n ion will be descri ed with f r nce to the accompanyin dr win form n a a t of the specification and in which:

Fig. l is an illustration, partly in cross-section, of an embodiment of the invention;- and Fig. 2 is an illustration of an alternate embodiment of the invention.

Referring to Fig. 1, there is shown an end portion of a coaxial transmissionline ll having a sheath conductor l3 and a concentrically arranged inner conductor l5ligidly held in place by means of a plurality of insulator members I1.

' faci itate such a preferably but not necessarily in the form ofans nular plugs which are held inplace either by crimping the sheath conductor as shown at lfl b y pins as shown at 2 I, or any other method known to those skilled in the art. In prior art-arrange ments, the end of conductor 15 is allowed to ride in the aperture of insulator H where the expansion and contraction of inner conductor 15 due to temperature variations, being different from that of. the sheath conductor, wonldintroduce dole, terious. efiects on the tuning of: the circuit in which the coaxial transmission line section is employed.

According to the invention, these disadvantages are eliminated by providing a conductive sleeve '23. which is. restrained from movement in the axial direction by insulating member 11- and sheath conductor [3. In the preferred arrange.- ment, insulator l1 and sleeve '23 are fastened to.- gether by slightly undercutting sleeve 23 for a portion intermediate its ends which is just sum.- .ciently long enough to accommodate the thick.- ness .of insulator H which is forced over the TB? mainder of sle ve 23. Sleeve '23, which may be a tubular member or which may be entirely close at one end as is shown, has. an annular groove 21 .milledin the inner wall thereof to accepts toroid l co l sp in 219 throosh t whi h inner conductor 1.5 o oo. line .1! slides to p ovide .cl ct leeve 23 su ta le for the low s encount r d hea th e d o t ransm ss on line. Prefe a l or ElQQ e :25 i f sui icicn epth tha onl a li ht sort-ion f coil sh ine 23. p otrude into bo e 25 oi s ee 23.. rde to retain the co oer e to the ins rtion o inner o ductor l5 o .25 an also to maintain the overalldimension of sleeve 23- at a minimum. While-the a ran ementhe h ss' li preferably in erted in o t e. audits location detcrmi ed l r 11. to sheath .c. an ally prior conductor 13 to fastenin 11 811 of the. cos: t

into sleeve 2:3 trans accommodate some form of tool, such as a tong.- like spanner, which may he used to slide the assembly comprising insulator ll and sleeve -23 in the axial direction in order to determine the optimum location of the sleeve.

Since it will be obvious that the tuning oi such a transm sio l i om wh t c l, the adjustment of the device may be more readily and accurately made with the arrangement shown in Fig. 2, wherein a plurality of slots 3| are milled into sheath conductor 13 of transmission line I I in a direction diagonally to the axis thereof and insulating member I! is held in place by means of studs 33 passing through slots 3 i. For clarity, the inner conductor l5, sleeve 23 and coil spring 29 are omitted from Fig. 2. Plate members 35 made of suitable resilient material are placed over studs 33 to serve both as coverings for slots 3| and also as lock washers for acorn nuts 36. The arrangement is tuned by loosening nuts 36 and exerting force to rotate member ll about the axis of transmission line H, which rotation will cause studs 33 to bear against the sides of slots 3i and force member IT to move in the axial direction. Once the tuning of the coaxial line section has been determined, nuts 36 are tightened and the transmission line will remain properly tuned despite temperature variations. The ratio of axial to rotational movement is varied by varying the angle at which slots 3| are milled, the optimum angle being that which will provide the desired range of tuning with the maximum rotation allowable under the particular circumstances.

While the invention has been described in terms of express embodiments, it is to be understood that obvious modifications thereof will be suggested to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. A coaxial transmission line section incorporating means to adjust the length thereof without deleterious effect thereto by reason of relative thermal expansion of the inner and sheath conductors of said line section, the sheath conductor of said line section having elongated slots arranged therein diagonally of the axis of said sheath conductor, a sleeve member surrounding the inner conductor of said line section, an insulating member fixed to said sleeve member, guid members fixed to said insulating member and arranged in the slots in said sheath conductor to cause said insulating member and said sleeve member to move axially in response to rotation thereof initially to adjust the length of said transmission line section, and a coil spring interposed between said sleeve member and said inner conductor to provide electrical contact therebetween without restraining relative movement in the axial direction therebetween to main tain the length of said transmission line section substantially constant as initially adjusted.

2. An open-ended coaxial transmission line section incorporating means to adjust the length thereof without deleterious effect thereto by reason of relative thermal expansion of the inner and sheath conductors of said line section, the sheath conductor of said line section having elongated slots arranged therein diagonally of the axis of said sheath conductor, a sleeve member surrounding the inner conductor of said line section and having an annular groove in the inner Wall thereof, an insulating member fixed to said sleeve member, stud members fixed to said insulating member and arranged in the slots in said sheath conductor to cause said insulating member and said sleeve member to move axially in response to rotation thereof initially to adjust the length of said transmission line section, and a coil spring arranged in the annular groove of said sleeve member to provide electrical contact between said sleeve member and said inner conductor without restraining relative movement 4 in the axial direction therebetween to maintain the length of said transmission line section substantially constant as initially adjusted.

3. An open-ended coaxial transmission line section incorporating means to adjust the length thereof without deleterious effect thereto by reason of relative thermal expansion of the inner and sheath conductors of said line section, the sheath conductor of said line section having elongated slots arranged therein diagonally of the axis of said sheath conductor, a sleeve member surrounding the inner conductor of said line section and having an annular groove in the inner wall thereof, an insulating member fixed to said sleeve member, stud members fixed to said insulating member and arranged in the slots in said sheath conductor to cause said insulating member and said sleeve member to move axially in response to rotation thereof initially to adjust the length of said transmission line section, locking means arranged on said stud members to fix the position of said sleeve with respect to said sheath conductor, and a coil spring arranged in the annular groove of said sleeve member to provide electrical contact between said sleeve member and said inner conductor without restraining relative movement in the axial direction therebetween to maintain the length of said transmission line section substantially constant as initially adjusted.

4. A terminating device for a coaxial transmission line having an inner conductor and a sheath conductor, the sheath conductor of said coaxial transmission line having elongated slots arranged therein diagonally of the axis of said sheath conductor, including a sleeve member surrounding the inner conductor of said line, an electrically spacing member fixed to said sleeve member to space the same from said sheath conductor, guide members fixed to said electrically spacing member and arranged in the slots in said sheath conductor to cause said spacing memher and said sleeve member to move axially in response to rotation thereof initially to adjust the length of said coaxial transmission line, and a resilient element interposed between said sleeve member and said inner conductor to provide elec-'- trical contact therebetween without restraining relative movement in the axial direction therebetween to maintain the length of said transmission line substantially constant as initially adjusted.

5. A terminating device for a coaxial transmission line having a conductive inner member and. a sheath conductor, the sheath conductor of said coaxial transmission line having elongated slots arranged therein diagonally of the axis of said sheath conductor, including a sleeve member surrounding the conductive inner member of said coaxial transmission line, one of said members having an annular groove in a wall thereof, an insulating member fixed to said sleeve member, stud members fixed to said insulating member and arranged in the slots in said sheath conduetor to cause said insulating member and said sleeve member to move axially in response to rotation thereof initially to adjust the length of said coaxial transmission line, and a resilient element arranged in said annular groove to provide electr cal contact between said sleeve memher and said conductive inner member without restraining relative movement in the axial direction therebetween to maintain the length of said transmission line section substantially constant as initially adjusted.

6. A terminating device for an open-ended coaxial transmission line having a conductive inner member and a sheath conductor, the sheath conductor of said transmission line having elongated -slots arranged therein diagonally of the axis of said sheath conductor, including a sleeve member surrounding the conductive inner member of said coaxial transmission line, one of said members having an annular groove in a contiguous Wall thereof, an insulating member fixed to said sleeve member, stud members fixed to said insulating member and arranged in the slots in said sheath conductor to cause said insulating member and said sleeve member to move axially in response to rotation thereof initially to adjust the length of said coaxial transmission line, and locking means arranged on said stud members to fix the position of said sleeve with respect to said sheath conductor, and a resilient element arranged in the annular groove of said one member to provide electrical contact between said sleeve References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,696,947 Flaherty Jan. 1, 1929 2,044,580 Leach June 16, 1936 2,082,860 Walter June 8, 1937 2,103,515 Conklin et al. Dec. 28, 1937 2,143,671 Zottu Jan. 10, 1939 2,280,728 Streib Apr. 21, 1942 2,379,047 Thomas June 26, 1945 2,449,479 Hopper et a1 Sept. 14, 1948 2,542,974 Abbot Feb. 27, 1951 2,548,881 Ferrill Apr. 17, 1951

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