US3763445A

US3763445A - Variable length transmission line

Info

Publication number: US3763445A
Application number: US00121807A
Authority: US
Inventors: D Hannaford; C Veenendaal
Original assignee: Tektronix Inc
Current assignee: Tektronix Inc
Priority date: 1971-03-08
Filing date: 1971-03-08
Publication date: 1973-10-02
Anticipated expiration: 1990-10-02
Also published as: CA945645A; DE2210965A1; NL7203047A; NL166586C; NL166586B; FR2128711A1; GB1350018A; FR2128711B1; JPS5539846B1

Abstract

A pair of movable U-shaped inner conductors for portions of a transmission line each have yoke elements secured to a slide positioned in a chamber in a metal housing and parallel leg elements slidably received in the ends of corresponding stationary tubular conductors also positioned in the housing and forming inner conductors of other portions of the transmission line. Two of the stationary conductors have other ends terminating in external connectors at one end of the housing and a third stationary conductor is U-shaped to provide a continuous inner conductor between the conductors. The casing is the outer conductor for the transmission line and has inner conducting wall surfaces spaced predetermined distances from the different portions of inner conductor to provide a substantially uniform characteristic impedance along the transmission line. A rotatable worm member journaled in the casing and threaded through the slide is rotatable to move the slides and U-shaped movable conductor members relative to the housing and stationary conductor members to vary the length of the transmission line.

Description

United States Patent [191 Hannaford et al.

[ VARIABLE LENGTH TRANSMISSION LINE [751 Inventors: David A. I-Iannaford, Beaverton;

Cornelis T. Veenendaal, Milwaukie, both of Oreg.

[73] Assignee: Tektronix, Inc., Beaverton, Oreg.

[22] Filed: Mar. 8, I971 [21] Appl. No.: 121,807

[52] US. Cl. .1 333/31 R, 333/33 [51] Int. Cl. H0lp 9/00, H01p 1/00 [58] Field of Search 333/31 R, 97 R, 96, 333/84 M [56] References Cited UNITED STATES PATENTS 2,440,089 4/1948 Haeff 333/31 R 2,721,312 10/1955 Grieg et al. 333/84 M 3,146,413 8/1964 Butler 333/31 R 2,502,359 3/1950 1 Wheeler 333/31 R 2,623,122 12/1952 Weber et al. 333/96 2,961,623 11/1960 Kuecken et al., 333/84 M X 3,005,168 10/1961 Fye 333/31 R 3,114,887 12/1963 Wedemeyer 333/84 M X 3,309,629 3/1967 Hessler, Jr. 383/97 R X 3,354,411 11/1967 Selby 333/97 R X 3,516,028 6/1970 Leef et al 3.33/31 R FOREIGN PATENTS OR APPLICATIONS 924,156 7/1947 France 333/31 R 833,511 4/1960 Great Britain 333/31 R OTHER PUBLICATIONS King, D. D. Measurements at Centimeter Wavelength," D. Van Nostrand Co., 1952 pp. 40-47. McAlister, K. R. A Variable-Length Radio Frequency Transmission-Line Section, Jr. of Scientific Instruments, Vol. 28, 5-1951 pp. 142-143.

Adey et al., A'Microwave Waveguide Trombone Phase Shifter, Canadian Jr. of Physics, Vol. 34, 1956, pp. 1112-1114.

I-Ioffswell, R. A., A Microstrip Line Stretcher," Review of Scientific Instruments, Vol. 41 -9-1970, pp. 1330-1331.

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Wm. I-I. Punter Attorney-Buckhorn, Blore, Klarquist & Sparkman [57] ABSTRACT A pair of movable U-shaped inner conductors for portions of a transmission line each have yoke elements secured to a slide positioned in a chamber in a metal housing and parallel leg elements slidably received in the ends of corresponding stationary tubular conductors also positioned in the housing and forming inner conductors of other portions of the transmission line. Two of the stationary conductors have other ends terminating in external connectors at one end of the housing and a third stationary conductor is U-shaped to provide a continuous inner conductor between the conductors. The casing is the outer conductor for the transmission line and has inner conducting wall surfaces spaced predetermined distances from the different portions of inner conductor to provide a substantially uniform characteristic impedance along the transmission line. A rotatable worm member journaled in the casing and threaded through the slide is rotatable to move the slides and U-shaped movable conductor members relative to the housing and stationary conductor members to vary the length of the transmission line.

799.1% wr n fi ures,

Patented Oct. 2, 1973 2 Sheets-Sheet 1 ATTORNEYS Patented Oct. 2, 1973 3,763,445

2 Sheets-Sheet 2 Ai A DAVID A. HANNAFORD IO 28 CORNELIS VEENENDAAL INVENTORS.

BUCKHORN, BLORE, KLARQUIST & SPARKMAN ATTORNEYS VARIABLE LENGTH TRANSMISSION LINE BACKGROUND OF THE INVENTION Prior attempts to provide transmission lines which can be varied in length while maintaining the characteristic impedance substantially uniformly along the line have, in general, employed arrangements in which portions of both the inner and outer conductors of the lines slide relative to other portions of such conductors. For example, one portion of the outer conductor of a coaxial line is slidable longitudinally into another portion of such outer conductor in telescoping engagement and simultaneously the corresponding portions of the inner conductor have similar telescoping relative sliding engagement. This type of structure is cumbersome and difiicult to fabricate since sliding joints must be provided for portions of both of the conductors. Also each of the sliding joints is a potential source of trouble since it is essential that good electric contact between the relative movable portions of each conductor be maintained at the point at which one portion of each conductor slidably enters the other portion of the corresponding conductor.

SUMMARY OF THE INVENTION In accordance with the present invention, a conducting housing, all portions of which are stationary, provides an outer conductor for a variable length transmission line and a portion of the inner conductor only is moved relatively to other portions of the inner conductor and the housing so that, in general, the number of sliding joints, requiring the good electrical contact referred to above, is one half of that of prior structures. Also the movable portions of the inner conductor are positioned in a chamber in the housing which provides guide surfaces for slides supporting and protecting this movable portion of the inner conductor and which can also house calibrated mechanism for moving such movable portions while maintaining the characteristic impedance substantially uniform along the transmission line.

It is therefor an object of the invention to provide an improved variable length transmission line in which the length of the line is varied by moving a portion of an inner conductor only relative to another portion of such conductor in a housing providing an outer conductor for such line, while maintaining the characteristic impedance of the transmission line substantially constant along such line.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a variable length transmission line in accordance with the present invention with the top cover mostly broken away and internal parts also broken away to show internal structure;

FIG. 2 is a longitudinal vertical section taken on the line 2-2 of FIG. 1;

FIG. 3 is a lateral vertical section taken on the line 3-3 of FIG. 2;

FIG. 4 is a view similar to FIG. 3, taken on the line 44 of FIG. 2;

FIG. 5 is a fragmentary vertical section on an enlarged scale taken on the line 5-5 of FIG. 1;

FIG. 6 is a fragmentary side elevation on an-enlarged scale of a sliding joint in the inner conductor of the transmission line;

FIG. 7 is a vertical section taken on the line 7-7 of FIG. 6;

FIG. 8 is a fragmentary vertical section on an en larged scale taken on the line 88 of FIG. 1;

FIG. 9 is a vertical section taken on the line 9-9 of FIG. 8; and

FIG. 10 is a vertical section on an enlarged scale taken on the line 10- 10 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The housing 10 of the transmission line is shown in FIGS. 1 and 2, and includes a body member 12 of rectangular shape in plan view provided with a cover member 14 of the same shape secured to the body member by screws 16. One end portion 18 of the body member 12 is of greater thickness than the remainder of such body member 12 and has a longitudinally extending rectangular channel 20 in its upper surface adjacent each of its sides and a similar U-shaped centrally disposed channel 22 also in its upper surface. The U- shaped channel 22 has a curved portion 24 adjacent the left of the end portion 18 of the body member 12 in FIG. 1 which connects straight portions of the channel 22 extending parallel to each other longitudinally of the body member. The channels 20 also extend parallel to the straight legs of the channel 22 and terminate at their left ends in FIGS. 1 and 2 adjacent but spaced from the left end of the body member 12. A bore 26 shown in FIGS. 1 and 8 extends into the left end 18 of the body member 12 in axial alignment with each of the channels 20.

The remaining thinner end portion 28 of the body member 12 has a generally rectangular recess 30 which terminates at one of its ends adjacent the thicker end portion 18 of the body member. The remainder of the recess 30 is bounded by side wall portions 32 and an end wall portion 34 integral with the body member 12.

The cover member 14 has an end portion 36 covering and fitting the upper surface of the end portion 18 of the body member 12 and an opposite end portion 38 covering the end portion 28 of the body member 12 and covering and fitting the top surfaces of the side walls 32 and end wall 34 of the body member 12. The upper surface of the end portion 28 of the body member 12 within the recess 30 is a plane except for a central longitudinal groove 35 which is opposite a similar groove 3 5a (FIG. 4) in a similar lower surface of the end portion 38 of the cover member 14 which is parallel and spaced from such upper surface to provide a rectangular chamber in the housing 10 having smooth and parallel inner top and bottom wall surfaces and smooth and parallel side wall surfaces.

Stationary tubular portions 40 of the inner conductor of the transmission line are supported in the channels 20 in the end portions 18 of the body member 12 by low loss insulating elements 42. Two of such elements 42 of generally rectangular cross section fit in each channel 20 and have semicircular grooves in their adjacent side surfaces receiving and fitting the tubular inner conductors 40. As shown in FIGS. 1 and 8, these inner tubular conductors 40 are connected adjacent the left end of the body member 12 in FIG. 1 to connectors 44 received in the bores 26 in such body member. These connectors have external connector portions 46 for connection to flexible coaxial cables or the like forming continuations of the transmission line of the present invention.

A stationary U-shaped tubular inner conductor 48 is similarly supported in the U-shaped channel 22 by similar straight insulating elements 50 and curved insulating elements 52. All of the tubular inner conductors have open ends 54 projecting a short distance into the chamber formed by the recess 30 in the body member 12. These ends 54 are slotted as shown most clearly in FIG. 6 to provide axially extending spring fingers 56 which are bent inwardly into resilient engagement with the straight legs of a pair of U-shaped slidable inner conductors 58 having curved portions 60 positioned in the chamber formed by the recess 30 in the body member 12. The legs of the conductors 58 are round in cross section and one leg of each of such conductors 58 is received in one of the straight tubular inner conductors 40 and the other leg of each conductor 58 is received in one of the legs of the U-shaped tubular inner conductor 48.

The curved ends 60 of the slidable U-shaped inner conductors 58 are flattened, as shown most clearly in FIG. 5, by removal of material therefrom and are each received in a semicircular groove 61 in each slide member of a pair of

slide members

64 and 66, both positioned in the recess 30 in the body member 12. The

slide members

64 and 66 each have a recess 68 (FIG. in their top portion for receiving a cover element 70. The semicircular groove 61 is positioned in a plane surface forming the bottom of each recess 68 and a corresponding semicircular groove is positioned in the lower surface of each cover element 70 to securely hold the curved portion 60 of the U-shaped sliding conductor 58 in the

respective slide member

64 or 66. Both the cover elements 70 and the

slide members

64 and 66 are made of low loss insulating material.

The

slide members

64 and 66 are moved in the recess 30 in the body member 12 of the housing by a worm 72 positioned between these slide members and rotatable in bearing elements 74 mounted in suitable recesses in the body member 12 and cover member 14 of the housing 10. The worm 72 extends parallel to the straight legs of the U-shaped sliding conductors 58 and as shown in FIG. 4, the grooves 35 in the body member 12 and cover member 14 of the housing 10 provide room for the worm. The sides of the

slide members

64 and 66 adjacent the worm have thread elements 76 engaging the threaded portion of the worm. A drive shaft 78 projects from one end of the worm 72 through the end wall 34 of the body member 12 of the housing 10.

It will be apparent that any suitable mechanism such as a manually rotatable knob on the drive shaft 78 can be employed to rotate the worm 72 to thereby move the

slide members

64 and 66 to slide the straight legs of the U-shaped sliding inner conductors 58 into and out of the tubular inner conductors 40 and the straight portions of the tubular U-shaped inner conductor 48. In a particular construction the range of sliding movement of the U-shaped sliding conductors was approximately 3 inches so that the change in length of the inner conductor of the transmission line effected by moving this range was approximately 12 inches. This change in length of the inner conductor effectively changes the length of the transmission line and the latter change in length is a linear function of the rotation of the worm 72. The range of this change in length may be made greater or smaller by changing the lengths of the respective portions of the inner conductors and the range of their relative movement, or providing a greater or lesser number of U-shaped sliding inner conductors and cooperating outer conductors.

The variable length transmission line of the present invention will ordinarily be connected by at least one of the connectors 44 to an external transmission line having a given characteristic impedance. The connectors 44 will be selected to have a substantially uniform characteristic impedance which is the same as that of the external transmission line. The housing 10 is made of metal or at least has electrically conducting interior surfaces in' the

channels

20 and 22 and the chamber provided by the recess 30 in the body member 12. The dimensions of the

channels

20 and 22 containing the tubular

inner conductors

40 and 48 are selected to provide, in conjunction with the outer diameter of the

tubular conductors

40 and 48 and the dielectric constant of the insulating

elements

42 and 50, this same characteristic impedance along the portions of the transmission line in which the tubular inner conductors are supported by such insulating elements.

The distance between the upper and lower plane surfaces in the interior of the chamber provided by the recess 30 in the body member 12 is also selected so that this distance in conjunction with the diameter of the exposed leg portions of the U-shaped sliding conductors 58 provides this same characteristic impedance. Since the curved portions 60 of these sliding conductors have insulating portions of the

slide members

64 and 66 positioned between such curved portions and the conducting plane surfaces of the chamber in which they are positioned, these curved portions 60 are reduced in thickness as shown in FIG. 5 to also cause the corresponding portion of the transmission line to have this same characteristic impedance.

There must necessarily be a change of diameter of the inner conductor of the variable length transmission line at each of the sliding joints between the sliding inner conductors 58 and the stationary

tubular conductors

40 and 48. As shown most clearly in FIG. 6, the ends 54 of these tubular conductors are tapered and the taper is selected and positioned relative to the ends of the insulating

elements

42 and 50 and the change in spacing of the inner surfaces of the outer conductor at the junction between the recess 30 in the body member 12 of the housing 10 with the

channels

20 and 22, including the small recesses 80 (FIGS. 1 and 10) which are present adjacent this junction as a result of a machining operation producing the

channels

20 and 22, to provide a substantially uniform characteristic impedance along the transmission line across this junction. This uniform characteristic impedance requires that there be good electrical contact between the sliding inner conductors 58 and the tubular

inner conductors

40 and 48 at the small end of the taper portion 54 on the tubular inner conductors. This is provided by the spring fingers 56 and by highly conductive corrosion resistance coatings, for example silver plating covered by a thin gold plating, on at least the portions of the conductors making the sliding joints between the stationary and sliding inner conductors. The result is an accurately variable length compact transmission line having a substantially uniform characteristic impedance along its entire length.

We claim:

1. A variable length transmission line comprising:

stationary outer conductor means surrounding stationary hollow inner conductor means defining coaxial transmission line means extending parallel to each other, adjacent outer ends of said stationary hollow inner conductor means being connected together by curved stationary hollow inner conductor means;

movable inner conductor means having parallel leg means each having one end received in sliding electrical relationship in one end of one of said stationary hollow inner conductor means and having connecting section means connecting the other ends of said leg means together;

' housing means having a recess therein with said movable inner conductor means being disposed therein and movable therea'long; said recess having conducting surface means provided by said housing means extending along each side of said movable inner conductor means and being spaced from said movable inner conductor means thereby defining an outer conductive means therefor so that said coaxial transmission line means, said conducting surface means and said movable inner conductor means provide said transmission line with substantially uniform characteristic impedance therealong;

slide means disposed in said chamber connected to said movable inner conductor means and being movable along said recess to move said movable inner conductor means relative to said housing means and said parallel leg means relative to said stationary hollow inner conductor means to vary the length of said transmission line; and b means connected to said slide means for moving said slide means and said movable inner conductor means along said recess.

2. A variable length transmission line comprising:

stationary outer conductor means surrounding stationary hollow inner conductor means defining coaxial transmission line means extending parallel to each other;

movable inner conductor means having parallel leg means each having one end received in sliding electrical relationship in one end of one of said stationary hollow inner conductor means and having connecting section means connecting the other ends of 45 and movable therealong; said recess having conducting surface means provided by said housing means extending along each side of said movable inner conductor means and being spaced from said movable inner conductor means thereby defining an outer conductive means therefor so that said coaxial transmission line means, said conducting surface means and said movable inner conductor means provide said transmission line with substantially uniform characteristic impedance therealong;

slide means disposed in said recess having insulation means connected to said connecting section means, said connecting section means being of lesser size than said leg means, said slide means being movable along said recess to move said movable inner conductor means relative to said housing ine ans and said parallel leg means relative to said stationary hollow inner conductor means to vary the length of said transmission line; and

means connected to said slide means for moving said slide means and said movable inner conductor means along said.recess.

3. A variable length transmission line according t d claim 1 wherein said coaxial transmission line means is disposed in said housing means and said conducting surfaces constitute said stationary outer conductor mans;

4. Ayariable length transmission line according to" claim 1 wherein said coaxial transmission line means are in parallel.

of said movable inner conductor means, said slide means having thread areas threadably engaging said worm member.

TA variable length transmission line according to claim 3 wherein said conducting surface means are positioned closer to said movable inner conductor means than said stationary outer conductor means are positioned with respect to said stationary hollow inner conductor means.

7. A variable length transmission line according to claim 3 wherein said connecting section means has an arcuate configuration.

fi t =0 0 i

Claims

1. A variable length transmission line comprising: stationary outer conductor means surrounding stationary hollow inner conductor means defining coaxial transmission line means extending parallel to each other, adjacent outer ends of said stationary hollow inner conductor means being connected together by curved stationary hollow inner conductor means; movable inner conductor means having parallel leg means each having one end received in sliding electrical relationship in one end of one of said stationary hollow inner conductor means and having connecting section means connecting the other ends of said leg means together; housing means having a recess therein with said movable inner conductor means being disposed therein and movable therealong; said recess having conducting surface means provided by said housing means extending along each side of said movable inner conductor means and being spaced from said movable inner conductor means thereby defining an outer conductive means therefor so that said coaxial transmission line means, said conducting surface means and said movable inner conductor means provide said transmission line with substantially uniform characteristic impedance therealong; slide means disposed in said chamber connected to said movable inner conductor means and being movable along said recess to move said movable inner conductor means relative to said housing means and said parallel leg means relative to said stationary hollow inner conductor means to vary the length of said transmission line; and means to said slide means for moving said slide means and said movable inner conductor means along said recess.

2. A variable length transmission line comprising: stationary outer conductor means surrounding stationary hollow inner conductor means defining coaxial transmission line means extending parallel to each other; movable inner conductor means having parallel leg means each having one end received in sliding electrical relationship in one end of one of said stationary hollow inner conductor means and having connecting section means connecting the other ends of said leg means together; housing means having a recess therein with said movable inner conductor means being disposed therein and movable therealong; said recess having conducting surface means provided by said housing means extending along each side of said movable inner conductor means and being spaced from said movable inner conductor means thereby defining an outer conductive means therefor so that said coaxial transmission line means, said conducting surface means and said movable inner conductor means provide said transmission line with substantially uniform characteristic impedance therealong; slide means disposed in said recess having insulation means connected to said connecting section means, said connecting section means being of lesser size than said leg means, said slide means being movable along said recess to move said movable inner conductor means relative to said housing means and said parallel leg means relative to said stationary hollow inner conductor means to vary the length of said transmission line; and means connected to said slide means for moving said slide means and said movable inner conductor means along said recess.

3. A variable length transmission line according to claim 1 wherein said coaxial transmission line means is disposed in said housing means and said conducting surfaces constitute said stationary outer conductor means.

4. A variable length transmission line according to claim 1 wherein said coaxial transmission line means are in parallel.

5. A variable length transmission line according to claim 1 wherein said means for moving said slide means includes a worm member journaled in said housing and extending along said recess parallel to said leg means of said movable inner conductor means, said slide means having thread areas threadably engaging said worm member.

6. A variable length transmissiOn line according to claim 1 wherein said conducting surface means are positioned closer to said movable inner conductor means than said stationary outer conductor means are positioned with respect to said stationary hollow inner conductor means.

7. A variable length transmission line according to claim 1 wherein said connecting section means has an arcuate configuration.