US2480462A - Tunable magnetron - Google Patents

Description

Patented ug. 30, 1949 Y 2,4so,4 62

Y TNABLE MAGNE'rnoN Howard W. Garbe, Hinsdale, Ill., assignor to Westernl Electric Company, Incorporated, New York, N. Y., a corpcration'of New York Application January 7, 1944, seriaiNo; 517,379

- 1 Claim. v 1

This invention relates to tunable magnetrons and more particularly to a method of and apparatusl for varying the output frequency of 'a magnetron oscillator. Y

Magnetron oscillators of the type consisting, in their simplest form, .of a two-element tube with a cylindrical plate structure and a co-axial filament used with a magnetic eld parallel to or nearly parallel to the lament, are Widely used as generators of ultra high frequency oscillations. In the operation of electronic apparatus employing a magnetron oscillator, it is sometimes desirable to be able to vary the frequency of the magnetron oscillator, as, for example, where the frequency employed is jammed by enemy action. While several methods are known for varying the frequency of magnetron oscillators, they involve ex# tensive changes in the tuning of the various elements of the oscillator circuit and cannot be readily employed.

An object of the present invention is to .provide an efiicient and effective method of and apparatus for readily varying the output frequency of a magnetron oscillator.

In accordance with one embodiment of this invention, the frequency of a magnetron oscillator may be switched to another predetermined frequency or several other predetermined frequencies by moving one or more plugs into one =or more of the planetary apertures of the magetron anc-de body to decrease the volumetric size of the resonant cavity, the plug being moved preferably by a loi-'metallic strip to which it is connected and whichis provided with a remotely controllable heater element.

Other objects and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the drawings, wherein Fig. 1 is a side elevation, partly in section, showing a magnetron oscillator tube constructed in accordance with one embodiment of the present invention;

Fig. 2 is a fragmentary, vertical sectional view along the line 2-2 of Fig. 1; and

Fig. 3 is an enlarged vertical sectional view along the line 3-3 of Fig. 2.

Referring now to the drawings and particularly to Fig. l thereof, a magnetron oscillator tube is there illustrated comprising a cylindrical anode block I0, which may be made of copper, and which has formed therein an axially extending cylindrical cathode chamber II in which a cylindrical cathode I2 is disposed having a suitable heater element positioned therein. Cylindrical recesses I3 and I 4 are formed in the right and left ends, respectively, of the block Ill, as viewed in this figure, and the ends' of the cathode I 2 extend into these recesses where they are connected to rigid supporting leads I5. The leads I5 are vertically disposed and their lowerk ends extend through tubular glass seals i6 mounted on the lower side of the anode block I0. Suitable current supplying means, not shown, may be connected to these leads to provide the current required for the cathode heater element.

Radially spaced about the cathode chamber Il are eight planetary axially extending cylindricalA apertures I1 which are connected to the center of the cathode chamber II by eight radial slots I8. .The cathodechamber, the planetary apertures and the slots cooperatively' form the resonant cavity, the volumetric size of which is one of the factorswhich determine the frequency of oscillation of the magnetron. Two small circular straps 20 are mounted in suitable circular recesses I9, formed at either'end of the anode block I0 within the recesses I3 and I4, as shown, and are Welded to alternate areas between the planetary apertures I1, while two other circular straps 2I of somewhat greater size than the straps 20 are mounted concentrically of the straps 20 and connect the alternate areas between the planetary holes not connected bythe straps 20. A pickup loop 22 extends downwardly from an output lead 23, which is mounted on the upper side of the anodev -block I0, into the-upper of the planetary apertures I ``I,the loop being electrically connected to the output lead 23.

End plates 25 are welded to either end of the anode block I0 and the entire tube is sealed against air. After the various parts of the tube have been assembled and the end plates welded into place, the air in the tube is substantially completely evacuated through a pumping tube 26 which is connected to the lower end of the anode block I0 and is spaced between the cathode lament leads I6, as shown in Figs. 1 and 2.

'I'he total volumetric size of the resonant cavity formed by the eight planetary apertures, the slots and the cathode chamber, directly affects Y the frequency of the magnetron oscillator, and a reduction in the total volumetric size will proportionately reduce this frequency of oscillation. By moving a plug 30, of suitable diameter to t closely within a planetary aperture, into one of these planetary apertures, it will be apparent that the volumetric size of the planetary apertures, and therefore of the resonant cavity, will be reduced. It has been found,4 in accordance with this in- 3 Vention, that by inserting a plug in one of the planetary apertures, the o-utput frequency of the magnetron oscillator may be materially changed and may be switched from the normal operating frequency to a, predetermined other frequency without aiecting the efficiency of the unit.

In accordance with one embodiment of this invention, which may. be practiced with very slight modicationof the magnetronunt, the plug 39 may be moved into the end of one of the planetary holes I1 by a bi-metallic element 3l which,

may be mounted, as shown in Fig. 3, in the pumpe ing tube 26. A heater element 32 is positionedadjacent the high expansive sideV ofi-the loi-metallic element 3l and is providedolvL extend through the base of the sealed pumping tube 26 and are lconnected toasuita'ble source 3 8 of current, such as a battery.` A switch 39 is provided for controlling the actuation of the` heater element 32. A bar 34 is.we1ded to the upper end of thebifmetallic s tripflA andthe upper end of thebar extends into a small, longitudinally ex. tending aperture35- formedmid-way between two of theA planetary holes il', as shown in Fig. 2.. An-

integrally formed rod shaped. portion 3 9 which extends to the. right, as shown in Fig. 3, ofthe. plug 30, is slidably positionedin the hole 35 and is provided with a notch 3.7.into which the.upper end of the rod 3,4'l extends. It will be apparent,

thus, that moving of the rod 34from one side .to 3, the other will causernovement of the plug 30.

either. into or outE of the planetary hole I'l with which it is associated. The bi-.metallic strip is.

preferably pre-loadedso that the operating temperature of the magnetron tube will not cause it to move, that is, the additionalheat of the heater element. 32 should be necessary to cause any` movement ofthe loi-metallic element 3l.

In the operation of the ,tuning device when it becomes desirable to change theJ4 frequency of oscillation. of the magnetronytube, the switch. 39 is closed and current is applied tothe heaterL element 32 to cause the b ifmetalli strip to move the rod attached thereto to the right as, viewed;

ieiFis- 3, This Causesihefplus @reenter the planetary hole l] withwliich it,isassociated.` It'V Wilbe apparent that the device.. couldbemade Continuously. adjustable by. employing a rheostat.

411V to adjust the current. suppliedl to the. .heater element-ginsteadof the Switchf. The tuning device could be made remotelycontrollable; by, locating the Switch. 3.9;.-011. theV control: panel 0f.: the apparatus.` with whiehthe magnetroniis. to,

be used.

While it is believed that the foregoing tuning device is the simplest method of readily varying the frequency of the magnetron oscillator and would involve the least modication of the magnetron tube, it would involve no departure from the spirit or scope of the present invention to substitute for the heater element and bi-metallic strip, a, solenoidy which obviously could be remotely controlled, or a, Sylphonv type bellows, either of which could be connected to the plug 30 so, as to impart the desired movement thereto, and, both of which could be operated by remotely controllable means.

What is claimed is:

A. variablefrequency magnetron tube including anv anode body having a cathode chamber, an aperture therein and a slot leading from said chamber to said aperture, a tubular pumping seal connected to said anode body for evacuating the air therefrom, a plug receivable in said aperture forl varying the volumetric size of the interior of said tube` to alter the frequency of. oscillation of the magnetron, a. bi-metallic strip mounted` within said tubular pumping seal and having its .V upper end movable upon the application of heat, means. movably connecting the upper end of said bi-metallic strip to saidy plug, means positioned in said pumping sealfor heating said bi-metallic strip to move said plug into or out of said aperture, and means extending out of said seal for supplying electrical current to said heating means.

HOWARD. W. GARBE.

REFERENCES CITED The following references are ofrecord inthe le of this. patent:

UNITEDA STATES PATENTS Number Name DateV 2,079,809;` Kuhle et al.V May 11, 1937 2,163,589 Dallenbach et al. June 27, 1939 2,259,690 Hansen et al. Oct. 21, 1941 2,306,860 Black Dec. 29, 1942 2,374,810 Fremlin May 1, 1945 2,408,234 Spencer Sept. 24, 1946l 2,408,817 Snow Oct. 8, 1946 2,414,496 Varian et al. Jan. 21, 1947 2,414,785 Harrison et al. Jan. 21, 1947 2,422,465y Bondley June 17, 1947 FOREIGN PATENTS Number Country Date 509,102 Great Britain July l1, 1939

Images