US2589903A

US2589903A - Tunable magnetron oscillator

Info

Publication number: US2589903A
Application number: US651924A
Authority: US
Inventors: Jr Albert L Vitter
Original assignee: US SEC WAR
Current assignee: United States, WAR, Secretary of; US SEC WAR
Priority date: 1946-03-04
Filing date: 1946-03-04
Publication date: 1952-03-18
Anticipated expiration: 1969-03-18
Also published as: GB653750A

Description

March 18, 1952 A. L. VITTER, JR

TUNABLE MAGNETRON OSCILLATOR 2 SHEETS-SHEET 1 Filed March 4, 1946 NQE INVENTOR ALBERT L. VITTER JR. BY

WMJQmAQ/MQ ATTORNEY March 18, 1952 A. VlTTER, JR

TUNABLE MAGNETRON OSCILLATOR 2 SHEETS-SHEET 2 Filed March 4, 19 46 v INVENTOR ALBERT L. VTTTER JR;

BY 4ep%9/-L mOE ATTORNEY Patented Mar. 18, 1952 UNITED STATES TUNABLE MAGNETRON OSCILLATOR Albert L. Vitter, Jr., New Orleans, La., assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application March 4, 1946, Serial No. 651,924

4 Claims.

My invention relates in general to electrical I apparatus and more particularly to magnetron oscillators.

The desirability of a tunable magnetron oscillator for radio frequency generation is well known to those skilled in the art. To provide compensation for unavoidable variations in the natural output frequency of a given oscillator which may be fitted into a pro-tuned system is highly desirable. Also adjustment of a radiated frequency should be possible to adapt a transmitter to changing desired operating conditions, to cite only two examples. It is therefore advantageous to be able to tune a magnetron mechanically over a band of operating frequencies. 18

In some communication systems a frequencymodulated microwave signal is necessary. For this type of operation a purely mechanical means of frequency changing is unsatisfactory and a more flexible and rapid means of altering a mag- 20 In accordance with the above, it is one object of my invention to provide a tunable magnetron oscillator.

Another object is to provide a magnetron oscillator adaptable to frequency modulation.

Still another object is to provide a novel method of coupling a stabilization cavity to a vane-type magnetron.

Briefly, my invention accomplishes these and further objects whichwill be apparent to those skilled in the art in the following fashion: to tune the magnetron mechanically, cylindrical members electrically connected to the magnetron casing are moved in the space immediately surrounding the magnetrons straps by means of a micrometer-like screw device; a stabilization cavity of the coaxial type is coupled to the oscillator by fastening the center conductor thereof to one of the vanes of the magnetron anode; to allow for frequency modulation, a portion of the center conductor of the stabilization cavity is flared into a plate and the corresponding section of the outer conductor is thickened so that a parallel plate capacitor is formed through which a variable beam of electrons from an electron gun, for instance, may be passed to alter the capacitive ef- Such de- 25 2 fect and hence modulate the magnetrons frequency.

The principles and operation of my invention will be more apparent to those skilled in the art upon reference to the following specification, claims, and to the drawings, in which:

Fig. 1 represents a perspective view of a vanetype magnetron anode with an attached stabilization cavity constructed in accordance with the principles of my invention;

Fig. 2 is a perspective view of the lid of the magnetron shown in Fig. 1 illustrating the details of the mechanical tuning system; and,

Fig. 3 is a sectional view of the stabilization cavity showing schematically an electron gun which is utilized to perform high frequency modulation of the oscillator frequency.

Referring now to Fig. 1, there is shown a magnetron anode consisting of a ring or cylinder 5 within which is radially mounted, in a well known manner, a plurality of equally spaced vanes or partitions 6 which divide the interior of ring 5 into individual cavity resonators. Straps 9 and III are provided to eifect additional separation between the various modes of oscillation which may be set up in the magnetron. The technique of strapping is well known in the art and will not 'be elaborated upon here.

In order to effect stabilization of the magnetron output frequency under changes in load conditions and other conditions which tend to produce undesirable alteration in the magnetron operation, a stabilization cavity is connected to the magnetron. This cavity comprises a box I2, along the long axis of which is positioned a central conductor l3. Box I2 is abutted against ring 5 and a hermetic seal is formed between the two members. Conductor I3 is brought through a hole l4 appreciably larger in diameter than the conductor in ring 5 and brazed directly to'the back of one of vanes 6. This type of connection affords exceptionally tight coupling between the magnetron and the cavity.

A portion I 5 of conductor I3 is flared transversely and the wall of box I2 is built out by means of a block 16 affixed to the box wall opposite the flared portion of conductor [3.

A standard output coupling means I! is con nected to ring 5 in such a fashion as to extract oscillatory energy from one of the resonant cavities between vanes 6. The bottom of ring 5 will, in practice, be sealed by a circular lid to allow evacuation of the tube. In addition, an emitting cathode will be placed in the central portion of the anode ring to complete the diode structure.

For purposes of simplicity of illustration, neither a cathode nor a lid, as described, are shown in the figure.

Referring to Fig. 2, there is shown a circular plate [8, shaped to flt tightly on ring 5 and which forms part of the magnetron shell. A screw l9 passes through a threaded hole in the center of the plate [8, and at the inner extremity of the screw is attached a disc to which are brazed, three concentric cylinders 2|, 22, and 23. The radial dimensions of these cylinders are such as to allow the cylinders, when plate [8 is placed snugly upon ring 5, to fit around and between straps 9 and [0. The screw (9 may be rotated to move the cylinders in and out of the space between straps 9 and Hi. This may be done by well known micrometer means.

A possible type of electron beam generating apparatus and a suggested location therefor is shown in Fig. 3 to which reference is now made. The figure represents a section through the longitudinal axis of box 12 and conductor l3 midway between the upper and lower surfaces of the box; The electron gun shown is of a conventional type consisting of an emitting cathode 25, a control grid 26, a pierced plate 21, a focusing electrode 28, an accelerating electrode 29, and a collecting electrode 30. Appropriate voltage sources are connected between the various electrodes of the electron gun as may be necessary for operation. Between the cathode and control grid 25 is connected a variable voltage source representing a modulating voltage which is used to provide the necessary variation in the density the capacitive effect between the former and the latter tends to load the magnetron and change the operating frequency of the tube in a manner which bears a relationship to the depth of penetration of the cylinder between and around the straps. Atno' time should there be physical contact between straps 9 and 10 and cylinders 2|, 2'2, and 23.

The stabilization cavity is especially designed to allow for more rapid changes in frequency in the oscillator. Due to the proximity of block IE to the flared portion l5 of conductor IS, the electric field between the members is quitestrong. When the electron gun shown in Fig. 3,. and which. is included in box l'2 ,directs a beam of electrons through the'space between members 15 and Hi, the dielectric constant of the intervening medium, normally a nearvacuum, is altered.

The resonant frequency of the cavity is therefore changed accordingly. Since the cavity is tightly coupled to the'magnetron, the frequency .of the latter is pulled from'its normal value.

put frequency of the magnetron. Frequency modulation with a swing of up to six megacycles has been accomplished by this type of electron tuning.

While there has been described what is at present considered to be a preferred embodiment of the present invention, it will be obvious to those skilled in the art that changes and modifications may be made therein without exercise of inventive ingenuity.

What I claim is:

l. A magnetron oscillator device comprising a vane-type anode electrode comprising a ringlike conducting member the interior of which is partitioned by a plurality of conducting vanes, a box of conducting material, a rod-like conducting member disposed substantially along the central longitudinal axis of said box, one portion of said rod-like conducting member being flared into a plate-like form in a plane containing said longitudinal axis, means thickening the wall of said box opposite one face of said plate-like portion of said rod-like member with the spacing between the two members substantially decreased, means joining said box to said ring-like member, and means joining one end of said rodlike member to one of said vanes whereby energy is coupled from said magnetron anode to said box.

2. A magnetron oscillator device comprising an anode electrode consisting of aring-like member the interior of which is divided into individual cavity resonators by a plurality of vanes disposed substantially along radii of said ring-like member, an external cavity resonator having a central coaxial conductor, one of said vanes extending through said ring-like member and being integral with said conductor.

3. Apparatus in accordance with claim 2 including means connected to said cavity resonator for altering the resonant frequency thereof.

4. Apparatus in accordance with claim 3, wherein a portion of said central conductor is flared into a plate-like form within said resonator, said means for altering the frequency of said cavity resonator including an electron discharge device within said resonator for generating an electron beam longitudinally to said flared portion, and means connected to said device for controlling the electron density of said beam, said last-named means serving to alter the dielectric constant of the medium between said flared portion of said central conductor and the adjacent wall of said resonator.

' ALBERT L. VIT'IER, JR.

REFEEENiJES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS