US2694795A - Cavity resonator - Google Patents

Description

Nov. 16, 1954 T. 'r. PUREKA CAVITY RESONATOR :5 Sheeis-Sheet 1 Filed July 31, 1951 IN V EN TOR.

THOMAS T. PUREKA Nov. 16, 1954 T. T. PUREKA 2,694,795

CAVITY RESONATOR Filed July 31, 1951 3 Sheets-Sheet 2 IN V EN TOR.

THOMAS T. PUREKA rfffrney NOV. 16, 1954 T, PUREKA 2,694,795

CAVITY RESONATOR Filed July 31, 1951 3 Sheets-Sheet 5 7/2 Qdllm mg United States Patent CAVITY RESONATOR Thomas T. Pureka, Lynn, Mass., assignor to the United States of America as represented by the Secretary of the Army Application July 31, 1951, Serial No. 239,484

3 Claims. (Cl. 333-83) greater, use is made of reflex velocity-modulation tubes.

An example of the latter is a IO-cm. oscillator identified in the trade as a Type 707A McNallytube. These tubes employ cavities as the resonant element which determines the frequency. A cavity resonator in this specific application of the same can be considered simply as a parallel resonant circuit placing an alternating voltage between two grids in the tube through which the electrons must pass.

Since there are wide variations between different operating conditions and between different tubes, such as in I the respective frequencies and outputs of the latter, it is essential that the associated mechanical tuning be adjusted so that the operating point falls at a point in the mode where the frequency can be shifted a reasonable amount in either direction with the electrical control without too much change in output power.

In the prior practice of using a wave guide for the resonant circuit of a velocity-modulation oscillator, there has been a practical limitation of two-to-one in the frequency range of the cavity because of wave-guide cut-off on the low-frequency end and the occurrence of multiple modes on the high-frequency end. In the various structures proposed heretofore for the purpose of avoiding such limitation, an example of which is shown in Patent No. 2,410,109, issued October 29, 1946, to John C. Schelleng, the improvement obtained in operating characteristics has only been of minor consequence. The reason for this can be attributed to the fact that in none of the designs of the prior art are both the width and length of the cavity changed simultaneously.

With the foregoing in mind, it is one of the objects of the present invention to provide an improved cavity resonator of the character referred to which has advantages over the various constructions proposed heretofore in the way of a substantial increase in frequency range possible and which, at the same time, is relatively simple in construction and manner of operation.

Other objects and advantages will hereinafter appear.

In accordance with the invention, adjustment of frequency range with a cavity resonator is accomplished by changing both width and length of the cavity simultaneously.

For the purpose of illustrating the invention, an embodiment thereof is shown in the drawing, wherein Fig. 1 is an elevational view, partly in section, of a cavity resonator having structural and operating characteristics in accordance with the present invention and mounted on a velocity-modulation tube of a conventional type, the section being taken on the line 1--1 in Fig. 2;

Fig. 2 is a plan view partly in section, the section being taken on the line 22 in Fig. 1;

Fig. 3 is a simplified view comparable to Fig. 2 and illustrative of the operating action in Figs. 1 and 2;

Fig. 4 is a view similar to Fig. 1, partly in section and illustrative of a modification, the section being taken on the line 4--4 in Fig. 5;

Fig. 5 is a plan view partly in section, the section being taken on the line 5-5 in Fig. 4; and

Fig. 6 is a simplified view comparable to Fig. 5 and illustrative of the operating action in Figs. 4 and 5.

In Fig. 1 reference numeral 10 designates a conventional reflex velocity-modulation oscillator of the Mc- Nally type aforesaid. About the tube gap and the usual cavity grids (not shown), is disposed a resonant cavity 11 embodying the present invention.

Cavity 11 comprises four driven members or parts 12, 14, 15 and 16 complementary to which, and slideable with respect to which, are four contact plates or follower parts 17, 18, 19 and 20. These eight parts, engaged and disposed as shown and together with top and bottom plates or casing parts 21 and 22, respectively, provide a cavity 23 about the gap of tube 10. The outer cylindrical wall or surface of tube 10 at the gap thereof is represented by the broken line 10a in Figs. 2 and 3.

It is well known that if the total volume of a cavity such as 23 is increased, the frequency of operation is decreased, and vice versa. For a detail treatise on the basic requirements and theory of operation of cavity resonators for the same or similar purposes as resonant cavity 11, reference is made to volumes 14 and 16 of Radiation Laboratory Series published 1948 by McGraw- Hill Book Company, Inc., of New York, N. Y., and to Principles of Radar copyrighted 1944 by The Technology Press, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Integral with each of the parts 12, 14, 15 and 16 are the respective similar racks 24, each of the latter being guided by and having a snug but sliding fit between plates 21 and 22. In mesh with each rack 24 is a pinion 25 journaled, as shown, in casing 21, 22 and integral or fixed for rotation with a gear 26.

In mounting cavity 11 on tube 10, a clamping ring 26 is first slipped over the same to about the position shown in Fig. l; a split, flexible washer 27 is forced over the usual contact discs 28 and 29; the casing assembly or unit is placed on the tube; a second, split, flexible washer 30 is placed against disc 28; and a second clamping ring 31 is screwed into plate 21. By tightening rings 26 and 31, the contact discs 28 and 29 are clamped tightly to the respective top and bottom plates of the cavity, for good radio-frequency contact.

The electrical characteristics of cavity 23 which is defined by the efiective or exposed surface portions of parts 12, 14, 15, 16, 17, 18, 19 and as well as by such surface portions of plates 21 and 22, are similar to those of a fixed cavity. For example, the resonant circuit is such that the maximum E field will appear across the tube gap.

Mounted on the top plate 21 and rotatable with respect thereto about the tube axis, is a frequency-adjustment knob or dial 32 the gear teeth 33 of which mesh with gears 26.

Upon rotation of knob 32 the identical gears 26 and the identical pinions integral or fixed with respect to the latter, are rotated simultaneously and in the same direction. Straight-line movement is thereby imparted to racks 24 and the associated members 12, 14, 15 and 16, but in different directions each of which is perpendicular to the tube axis. If knob 32 is rotated counterclockwise, as viewed in Figs. 2 and 3, members 12, 14, 15 and 16 will recede simultaneously and by the same amount measured radially from the tube axis. Such action will be accompanied by similar and simultaneous recession of the associated followers or contact plates 17, 18, 19, and 20 and further and corresponding compression of the coil springs 34 which maintain good contact between the sliding surfaces of all parts. In Fig. 3 the various parts are shown receded to a position whereat cavity 23 is expanded, the total volume being substantially greater than that in Figs. 1 and 2.

To facilitate assembly, the casing has been shown as being comprised of the two plates or sections 21 and 22 which may be welded, cemented or otherwise secured together at the respective adjacent edges of the same, i. e., along the line 21a. For the same purpose, one or both of the casing sections 21 and 22 may be made up of two or more parts suitably secured together after assembly. All parts are made of material having a relatively high coeificient of electrical conductivity.

Figs. 4, 5 and 6 illustrate a modification or alternative form wherein there are but two simultaneously receding driven members 12a and 15a and but two associated followers or contact plates 17a and 19a. In all other respects, the structure and operating action of the various parts are substantially the same as in Figs. 1, 2 and 3.

For purposes of calibration, an appropriate scale may be engraved or otherwise placed on the beveled edge of the frequency-adjustment knob or dial 32'. It is also proposed to employ a set-screw or other suitable means to hold knob 32 against accidental rotary movement from any position of adjustment.v For example, arubber band or split ring .35 may be inserted between knob 3.2. and the central cylindrical portion of plate 21 on which the knob. is mounted, The grip or spring-action of band 35 is made sutficient to hold the various parts. against creepage such as might be caused by the constant and inwardly-directed forceexerted on each rack 24 by the associated spring 34.

It will be understood that various other modifications, such as in the size, shape and arrangement of the parts, are possible without departing from the spirit of the invention or "the scope of theclaims.

What is claimed is:

1. A cavityresonator comprising a plurality of movable contiguous dri-ver and follower walls surrounding and symmetrical about a given. longitudinal axis, said walls. being alternately disposed with. respect to each other, each of said walls having a sliding contact with the walls. adjacent thereto, whereby said walls define said cavity resonator; a housing for said driver and said follower walls, each of said follower walls including a longitudinal member disposed within a keyway therefor in said housing, a spring disposedbetweenone end of each longitudinal member and the endof its respective keyway to maintain said follower walls in positive contact with said driver walls in all positions of said driver walls, each of said driver walls including arack portion disposed withina keyway therefor in said'housing; and meansfor simultaneously-moving alla of said walls comprising a pinion meshed withtthe rack. portion. of each of said driver parts, gear means. attached toeach of said pinions and a toroidallyshaped knob. havinga geared surface, said gear means beingv meshed with said geared surface of said knob.

2. A cavity resonator, asdefined. in claim 1, wherein there are at leastfourdriver walls disposed. at 90 intervals. about saidilongitudinal. axis, each: of said driver walls including-an isosceles. right-triangular portion disposed; within said; housing, the junction of the legs of said triangularportion. being attached to. one end of said rack portion, and wherein there are at least four follower walls, each of which is symmetrically disposed between each of said driver walls, each of said follower walls including a contact plate disposed within said housing and attached to the other end of said longitudinal member, said contact plate being spring-pressed into contact with a pair of colinear legs of adjacent triangles, said legs of said triangular portions being no more than one half the length of said contact plate when the distance between said driver walls and said longitudinal axis is at its minimum limit.

3. A cavity resonator as defined in claim 1, wherein there are at least two driver walls disposed at 180 intervals about said longitudinal axis, each of said drivers including an isosceles right triangular portion disposed within said housing with the junction legs of said triangular portion attached to one end of said rack portion, and wherein there are at least two follower walls each of which is symmetrically disposed between each of said driver walls, each of said follower walls including a longitudinal member disposed within said keyway .with a wall section attached to the other end of said longitudinal member, said wall section being perpendicular to said longitudinal. member and having two oppositely disposed contact sections, each of said contact sections atfixed to an end of said wall section. at a 135 angle whereby said contact sections are spring-pressed into contact with adjacent legs of said two triangularportions, saidlegs of said triangular portionbeing, at most, the same length as said contact sections.

References Cited in the file of this patent UNITED STATES PATENTS 62 Great-Britain Jan. 7', 1857

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