US2520614A

US2520614A - Variable coupling device

Info

Publication number: US2520614A
Application number: US650369A
Authority: US
Inventors: Robert L Sproull
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1946-02-26
Filing date: 1946-02-26
Publication date: 1950-08-29
Anticipated expiration: 1967-08-29
Also published as: GB635619A

Description

A$29, 1950 R. sPRoULl. 2,520,614

VARIABLE couPLING DEVICE Filed Feb. 2s, 194e l @EME Patented Aug. 29, 1950 VARIABLE `CUPLING' DEVICE Robert L. Sproull, Princeton, N. J., assignor to Radio Corporation of 1AAmerica, a corporation of Delaware Application February 26, 1946, Serial No. 650,369 v 2 Claims. (Cl. 178-44) This invention relates generally to microwave i apparatus and more particularly to improved variable-coupling wide-frequency-band tunable microwave resonators of the type utilizing a movable piston wherein adjustment of thel piston for conductive piston enclosed within the resonator shell. Well known methods of coupling into or out. of such adjustable resonators include the use of microwave probe elements, coupling loops and adjustable aperture devices, depending uponA the characteristics of thev circuit to which the resonator is coupled. It. is frequently advantageous tobe able to vary the degreey of couplingbetween an external circuit and the microwave resonator as the resonator is, tuned through its useful. frequency band. In particular in reex oscillators of the type including an electron.v reflecting electrode, it is desirable that. the coupling coefficient between the oscillator and the load circuit remain substantially constant or decrease as the oscil lator frequency is increased. A conventional cou- 'pling loop, probe or aperturey device. coupled into the oscillator cavity normally will provide an increased coupling coeiiicient as the frequency is increased, thereby providing non-linear loading of the, oscillator over its useful frequency range.

The instant invention is related toand comprises anl improvement over the devices disclosed in the copending U. S. application of Ernest G. Linder, Serial No. 650,719; filed February 27, 1946, covering several embodiments of microwave appaifa-tus wherein the frequency 0f, a microwave. resonator is varied by longitudinal'adjustment of a piston operative. therein, and whereinthe effective length of a microwave, coupling probe, or the originar-displacement of a coupling loop aswell as` the effective opening of an aperture device is simultaneously adjusted by movement of the tuning piston. The invention asl disclosed therein provides means for tuning a. microwavegenerator and simultaneously adjusting the coupling thereto from an external coaxial line or Waveguide device.

In contradistinction thereto, the instant invention comprises a variable-coupling wide-frequency-band microwave coaxial lline resonator 2 A including a movable piston having an aperture therein disposed within and between the resonator conductors. A coupling loop of uniform cross.- section terminates a coaxial line connected to an external device. The loop extends through the resonator and through the aperture in the tuning piston. Longitudinal adjustment of the tuning piston thus controls the resonatorI frequency and the coupling coefficient of the loop in opposite sense. Since there is no contact between the loop and the movable piston, the commonly erratic characteristics of movable contacts at microwave frequencies is eliminated insofar as coupling is concerned. A4 modification of the invention utilizes a coupling loop having a'. tapered crosssection wherein the coupling coefficient changes in accordance with a predetermined non-linear function of the resonant frequency of the resonator.

Among the objects of the instant invention are to provide an improved method of and means for simultaneously adjusting the tuning and coupling of a microwave resonator device. Another object of the invention is to provide a method of' and means for tuning a coaxial microwave resonator over a relative wide frequency range and for simultaneously adjusting the coupling coefficient' of a coupling element connected to an external circuit. A further object of the inveni tion is to provide an improved coaxial microwave resonatory including a longitudinally adjustable tuning piston, wherein adjustment of the pistonV simultaneously adjusts the effective coupling to the resonator of a `microwave coupling loop. Another object is to provide an improved' coaxial' microwave resonator including a longitudinally adjustable tuning piston, wherein adjustment of the piston simultaneously adjusts the effective coupling of a microwave coupling loop having a predetermined" tapered conformation for coupling an external circuit to said resonator according to aV predetermined function of the operating frequency;

An additional object is to providev an improvedI variable-coupling wide frequency' band' microwave resonator including a frequency adjusting piston wherein adjustment of the tuning piston simultaneously varies in opposite sense the reso nant frequency of said' resonator andthe coupling coefficient of a coupling loop coupling said resonator to an external circuit. A further object is to provide a constant-coupling wide-frequencyband microwave resonator including a movable tuning piston wherein adjustment of the tuning piston varies the resonant frequency of said resoelevational View of a second embodiment of the invention. Similar reference charactersV are applied to similar elements throughout the drawing. l

Referring to Figures 1 and 2 of the drawing, a typical microwave resonator according to the invention includes inner and outer coaxially disposed conductors I, 3, wherein the outer conductor includes a closed end portion 5. The resonator is tuned by means of a longitudinally adjustable piston 'l having an aperture 9 disposed therein in the region intermediate the inner and outer coaxial line conductors. adjustment of the piston 1 may be accomplished by means of actuator bars IB connected to any desired type of actuating mechanism not shown.

Y The piston 'l includes a pair of cylindrical slotted contact elements Il, i3, which contact the outer and inner resonator conductors, respectively, to insure uniform electrical contact with the piston.

A second coaxial line having an outer conductor I5 and an inner conductor l1 is terminated withinthe tunable resonator by means of a hairpin coupling loop I9. The coupling loop I9 extendsthrough the portion of the resonator intermediate the end face 5 and the tuning piston 1 and also extends through the aperture 9 in the tuning piston '1.

Thus, as the resonant frequency of the resona- 1 tor l is increased by advancement of the piston face toward the end resonator wall 5, increasingly shorter portions of the coupling loop are exposed to the resonator cavity, thereby correspondingly tending to reduce the coupling betwen the resonator and the external coaxial line i5, l?. The

The longitudinal sense to the variation of the resonant frequency of the resonator as the piston position is adjusted.

It should be understood that the variableor constant-coupling systems disclosed herein may be employed as either output or input coupling elements for associated circuits and that simultaneous or separate control of a plurality of such coupling elements may be provided for a single resonator or for a plurality of resonators. By proper proportioning of the adjustable resonator and the associated coupling loop or loops, the coupling coefcient to external circuits may be kmaintained substantially constant or varied in opposite sense to the adjustment of the resonator frequency.

Thus, the invention disclosed comprises several embodiments of coaxial resonator wide-frequency-band microwave devices providing tuning and frequency variation by adjustment of a tuncoupling from the masked portion of the loop through the aperture B to the resonator cavity is practically negligible. Depending upon the circuit parameters, the coupling coeflicient to an external circuit, not shown, may be maintained substantially constant throughout the useful frequency range of the resonator, or the coupling coi e'icient may be reduced as the frequency is .in-

creased. Since the loop does not contact the movable piston and is xed `with respect to the resonator walls, erratic operation due to varying contact resistances is minimized.

The'device illustrated in Figure 3 is similar to that described Vby reference to Figures 1 and 2,

with the exception that the coupling loop i9 is of non-linear cross-section, whereby longitudinal adjustment of the tuning piston i varies the coupling coelcient of the coupling loop I8' according to a non-linear function of the operating frequency of the resonator. It should be understood that the shape of the coupling loop l 9 Vmay be varied in accordance with the desired coupling coefficient characteristic to provide either constant coupling or variable `coupling in opposite ing piston, wherein such piston adjustment provides corresponding control of the coupling coeincient between said resonator and an external circuit. Y

I claim as my invention:

1. A constant coupling wide-frequency-band tunable microwave resonator including a coaxial line section, means including a movable piston having an aperture therethrough disposed within and substantially'conforming to rsaid section and comprising with said line section said tunable resonator, and a, U-shaped coupling loop extend# ing into said resonator through the wall of said resonator opposite said piston andv having a U-shaped portion'of said loop extending through said aperture in said piston for microwave coupling to said resonator, whereby adjustment of said tuning piston varies the reso-nant frequency of said resonatorand the'coupling coefhcient to said resonator of said coupling loop in predeter- `rnined relative sense and degree.

2. A constant coupling wide-frequency-band tunable microwave resonator including a coaxial line section, means including'a movable piston having anaperture therethrough disposed Within and substantially conforming to said section and comprising with said line section said tunable resonator, anda U-shaped coupling loop of predetermined tapered width extending into said resonator through the Wall of said resonator opposite said piston and having a U-shaped portion of said loop extending through said aperture in said piston for microwave coupling to said resona-f tor; whereby adjustment of said tuning piston varies the resonant frequency of said resonator Without substantial variation of the coupling coeilioient to said resonator of said coupling loop.

ROBERT L. SPROULL.

REFERENCES CITED The following references are of record in the ille of this patent:

l UNITED STATESv PATENTS