US2950416A

US2950416A - Magnetron output control

Info

Publication number: US2950416A
Application number: US640566A
Authority: US
Inventors: William C Brown
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-02-15
Filing date: 1957-02-15
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

Aug. 23, 1960 Filed Feb W. C. BROWN MAGNETRON OUTPUT CONTROL 2 Sheets-Sheet l INVENTOR. Mum/1 c? Bra/w Aug. 23, 1960 w. c. BROWN 2,950,416

MAGNETRON OUTPUT CONTROL Filed Feb. 15, 1957 2 Sheets-Sheet 2 INVENTOR. M4 am 47 EEO/WY limited States Fat-ens MAGNETRON OUTPUT CONTROL William C. Brown, Weston, Mass., assignor to the United States of America as represented by the Secretary of the Air Force Filed Feb. 15, 1957, Ser. No. 640,556

Claims. (Cl. SIS-39.69)

This invention relates to high frequency oscillators of the magnetron type, and more particularly to the control of magnetron output. The invention is directed to methods and means for reducing the incidence of unwanted frequencies, or modes of oscillation, in the operation of a magnetron.

In oscillators of the type considered here, known as plural cavity magnetrons, there is commonly an incidental generation of undesired frequencies or modes of oscillation accompanying the generation of the desired frequency or mode of oscillation as, for example, the pi mode. This incidental generation of other modes causes a lowering of the efficiency, and a somewhat erratic functioning, of the magnetron.

Many procedures have been considered as potential correctives or palliatives for this condition, among them the procedure of strapping alternate vanes together, or the use of an auxiliary cavity coupled to the magnetron through a suitable transmission line or other coupling technique. Another method has involved employment of transmission line theory by leading off an undesired frequency or mode of oscillation by way of an extra o'r auxiliary element of selected length to resonate at an undesired adjacent frequency.

Each of these procedures or methods has been successful to a degree, but each is subject to difficulties and complications in manufacture and adjustment. Strapping, for example, tends to eliminate a great deal of erratic changing of modes, but does not actually eliminate the undesired modes of oscillation, per se. Instead, there is a tendency for the separation of modes to increase. Furthermore at frequencies above 10,000

mc./sec. straps become quite small and mechanically difiicult to incorporate, and their small dimensions result in large copper losses and lowered efficiency. Again, in the use of a transmission line to lead olf unwanted frequencies through an external auxiliary cavity, and to an external auxiliary load, the apparatus becomes bulky, difiicult to adjust and expensive. Similarly, in the use of an extra resonant element there is a difficult problem of adjustment to the exact length required. Moreover, such procedure can produce the suppression of only one frequency or mode of oscillation for each such extra element employed.

It is an object of this invention to reduce the incidence of unwanted frequencies or modes of oscillation by means incorporated within the magnetron. It is a further object of this invention to provide a method and means to accomplish the above result Whether the magnetron is tuned or untuned, and whether the cavities are strapped or unstrapped; the method of the invention involving the establishment of a secondary or shunt circuit linking equipotential regions in adjacent cavities in such a manner as to tend to maintain the magnetron in operation in the pi mode, exclusively, by minimizing energy dissipation through said shunt link.

Other objects of this invention will be apparent as the tta fj Patented Aug. 23, 1969 Figure l.

in the drawings reference numeral 10 designates the shell of the magnetron, 11 the end caps, 12 and 12 the vanes, 13 the cavities, 14 the cathode, 15 the cathode and filament leads, 16 and 16 loops of lossy material connecting adjacent cavities, 17 a slot in one or more vanes to accommodate the connecting loop, and 18 the output loop for delivery of the generated power to theantenna or other utilization element.

Operating current is supplied to the cathode by way of leads 15; and with magnet poles 19 so placed that the magnetic field is parallel to the axis of the cathode, the oscillations set up in the magnetron will be at a frequency which is primarily determined by the dimensions of the cavities 13, but other factors may tend to produce oscillations in different modes. In the preferred pi mode, the oscillations will be such that the flux densities in adjacent cavities will be equal and the voltages induced equal and out of phase. In all other modes the fiux densities will be unequal and the voltages induced will be unequal.

To reduce the incidence of these undesired modes of oscillation and to tend to induce the pie mode of oscillation, the present invention introduces a flux-linking energy-

shunting element

16 and 16 in the form of a loop of lossy material extending into and fastened to the walls of two adjacent cavities, as indicated in Figures 1 and 4. Figures 2 and 3 show variants of this loop.

Since in the pi mode of oscillation the flux linkages in adjacent cavities are equal and the voltages induced are equal, and 180 out of phase, there will be zero or near zero current flow in the lossy material, and little loss if any, during operation in this preferred mode.

In any other mode of oscillation the flux linkages will be unequal, hence the voltages will be unequal and there will be current flow in the lossy material with resultant loss. Now inasmuch as the inherent tendency of any magnetron is to operate in that particular mode which tends to minimize losses due to inter-cavity coupling effects, the result will be the establishment of a marked preference on the part of the magnetron to maintain the pi mode of oscillation in order to minimize coupling between the primary (cathode to anode) circuits, on the one hand, and the secondary (loop 16) circuit on the other. Thus the incidence of unwanted modes is minimized.

While I have described and shown only one loop of lossy material connecting adjacent cavities in a vane type of magnetron it is understood that more than one or all of the cavities may be so connected and that the device may be incorporated in magnetrons with any other form of cavity. Similarly, other modifications within the spirit and scope of the invention will be apparent to those skilled in the art. Hence the invention is to be understood as limited only as indicated in the appended claims.

What is claimed is:

1. In a magnetron comprising adjacent resonant cavities adapted to develop voltages that are of equal magnitude, but opposite polarities, during operation in the preferred mode, means'for damping out unwanted oscillations, comprising a secondary circuit connecting two of said adjacent cavities, said secondary circuit consisting of a single shunt loop having one half its length disposed within one of said two adjacent cavities, and theother half of its length disposed within the other of said two adjacent cavities, said shunt loop being of a composition tending toestablish'substantial energy dissipation only 7 when such unwantedoscillations occur. 7 a

2. In a magnetron assembly, an anode element having a circular periphery, with cavity-forming digits intruding radially inward from said periphery, and mode-locking means disposed entirely within said periphery, said mode- 7 locking meansincluding a shunt loop ofrlossy material spanning the digital intrusion between two adjacent cavi- V ties, and having its respective termin als in the arcuate. portions of said circular periphery. that form the respec-" ,tive outer boundaries of said cavities. a

3 In a magnetronassernbly, ananode element having a PfiIipheral wall, with cavity-forming digits intruding radially inward from said peripheral wall, and modelocking means consisting of a shunt loop of lossy material penetrating the digital intrusion between two adjacent 4 V cavities, and having its respective terminals in the arcuate portions of said circular periphery that form the respective outer boundaries of said cavities.

i 4. In a magnetronassembly, an anode element having 5 a peripheral wall, with cavity-forming digits intruding radially inward from said peripheral wall, and a modelocking loop of lossy material disposed in symmetrically straddling relationship tothe digital intrusion between two adjacent cavities, said mode-locking loop having one-half '10 its length positioned within one of said cavities, and the other half positioned within the other of said cavities;

5. In a magnetron assembly, an anode element having 7 v a peripheral wall, with cavity-forming digits intruding radially inward from said peripheral wall,- and a loop of 15 lossy material fastened'at its two ends to said peripheral De Vore Feb, 14; 1950' Heising Apr. 178, 1950