US2778975A - Magnetrons - Google Patents

Description

Jan. 22, 1957 R. DUNSMUIR ET AL MAGNETRONS Filed Nov. 13, 1953 UnitedStates Patent O MAGNETRONS Robert Dunsmuir, Rugby, Thomas William vCeri Fisher, Lilbourne, near Rugby, and Nigel Sutton Nicholls, Malvern, England, assignors to The British Thomson- Houston Company Limited,.a British company Application November 13, 1953, Serial No. 391,926

Claims priority, application Great Britain November 18, 1952 3 Claims. (Cl. S15-39.69)

This invention relates to the construction. and operation of electron discharge devices known as magnetrons.

It has been customary in the past to strap alternate segments of the anode structure of such devices in order to lock the oscillation in the 1r-mode since alternate segments in that mode oscillate in phase. For this purpose the strapping has usually been carried out at one or both ends of the anode structure. lt is also known to locate the straps within a circumferential groove opening into the anode-cathode space at a point intermediate the ends of the structure. lt' the anode structure is built up of laminations it is further known to form straps integrally with selected ones of the laminae so that when the laminae are stacked into the usual block form, continuous coaxial straps are distributed, duplicated as vrequired, along the axis of the bore of the anode structure. This disposition of coaxially arranged axially displaced straps for the sake of brevity will hereinafter be referred to as distributed strapping.

While the aforementioned prior art is mainly concerned with the modification and control of the circumferential patterns of the resonant modes, control of the axial patterns by distributed strapping seeks to keep to a minimum the R. F. voltages and currents in the anode for a given power level and to prevent oscillation in modes inl which the two ends of the anode structure are in phase opposition.

This invention consists in a non-laminated anode structure in which alternate segments are connected by displaced strapping and in which the faces of the segments facing the cathode present unbroken surfaces.

According/to the invention an electric discharge device of the magnetron type having an anode structure comprising a cylindrical yoke member adapted to receive and to have lixed therein a plurality of radially inwardly extending anode segments, said segments each having a plurality of holes positioned transversely of the segment and parallel to the inner edge thereof, the holes being of large and small size in alternate segments and threaded, during manufacture, by straps which contact with the periphery of the smaller holes and are spaced from the periphery of the larger holes so as to connect alternate segments together when assembled in the yoke member.

The invention will be better understood from the fol lowing description, reference being had to the accom* panying drawing in which Fig. l is a voltage curve of a magnetron of the usual type, Fig. 2 is a similar voltage curve of a magnetron constructed according to this invention, Fig. 3 is a plan view and Fig. 4 a sectional elevation on the line X-X in Fig. 3 of our improved magnetron.

Referring iirst to Fig. l this shows a typical curve of voltage between segments along the axial length of the magnetron for a conventional tube with straps at the end faces a and b. It will be seen that not only is it a poor characteristic because therel is considerable vari ation in voltage along the segments, but the maximum "ice voltage V1 occurs in the vicinity of the straps, where breakdown is more likely to occur. With the straps distributed along the axial length of the anode at points c` to j, according to this invention the characteristic of theV voltage between the segments becomes as shown in Fig. 2.. The precise shape of the characteristic will depend on the number and disposition of the straps, but the curve in Fig. 2 is a representative curve for a tube with eight straps disposed equidistantly along the axial length of the anode. The number of straps per unit axial length of anode structure should be as high as possible subject to maintaining clearances from strap to strap or strap to segment, and convenience of construction.

It is obvious that for the same maximum voltage between segments the general voltage level could be raised to the position shown by the dotted curve in Fig. 2 witha corresponding increase in power handling capacity;

One method of constructing a valve according to this invention is illustrated in Figs. 3 and 4. As shown ali the segments K are made as separate parts, and are drilled to take the straps m which may be made up in the form of rings of circular cross section material. Alternate seg` ments will have large clearance holes n for the straps to pass through, and the holes along any one segment will be alternately clearance and itting holes. The segments are then threaded on to the straps m, and then fitted into slots in the cylindrical yoke body member o before the whole: assembly is brazed.

A further advantage of the above method of construe-- tion is that the wavelength of the 1r and 1r are separated more widely, so that 1r' mode is far less liable to be ex` cited and the valve will oscillate more reliably on the correct mode.

The relation between 1r and 1r' modes can be understood by considering two separate anodes, formed by splitting a given end strapped anode at its central transverse plane. Apart from small end elfects, a half anode has the same vr mode wavelength as the whole, since in the 1r mode there is no current running along the segments across the central plane. If the two half anodes are completely uncoupled they may be excited to oscillate at the same frequency but in any relative phase. For example, they may be in phase (corresponding to the 1r mode) or in phase opposition (corresponding to the 1r mode). VWhen the halves are brought together, the frequency of the 1r mode depends on the tightness of coupling (the tighter the coupling the further apart are vr and 1r' modes) as is desirable.

and the bore, which is approximately proportional to the.

distance between straps. It is clearly desirable to mini-v mise this distance as for example by putting straps at a; point intermediate to the ends of the anode structure, but this would lead to voltage variation. To keep down theaxial inductance of the segments it is important to avoid'. any discontinunity in the segment faces. By our inven tion a satisfactory way of obtaining both desirable features is achieved simultaneously.

The invention is not in any way 4to be ylimited to the particular embodiment illustrated by a vane type merle structure in the drawing since any reference to segments hereinbefore shall apply equally to segments which, when assembled in the described manner form anode structures of the .types commonly `referred to as hole and slot or parallel slot.

What we claim as new and desire to secure by Letters Pat-ent of the United States is:

1. In an electron discharge device of the magnetron type, an anode structure, comprising in combination, a

In an end strapped tube`A axial currents flow to feed the endstrap capacity, and' these currents constitute the coupling for the 1r mode.v They are limited by the inductance in the axial direction represen cylindrical-,yoke member, a plurality of radially inwardly extending separate anode segments, each .of said .segments having a passage therein positioned transversely and parallel to the inner edge thereof, said passages being er large and small `size in alternate segments and Yhaving Ithreaded .therethrnugh a strap contacting the lperiphery of said small passages andspaced rom the peripheryof said larger passages, to connect together the alternate assembled segments.

In an electron discharge device of the magnetron type, an annde structure, comprising in cambi Stien, a cylindrical yoke member, a plurality or radially inwardly ext-ending `serntrate anode segments ixed within said yoke, each of said segments having a plurality of transverse passages positioned parallel to the edge thereof, said passages being of ylarge and srnall size in alternate segments and having threaded therethrough centimeter straps contesting the periphery sf the small passages and spaced from ,the periphery of the larger passages, so as to conneet together alternate `segments of said assembled anode.

3, In an electron discharge `device of Athe magnetron l type, an anode structure, comprising in combination, a

cylindrical yoke member, a `plurality of radially inwardly extending anode segments positioned Within said yoke, each of said segments having a plurality of axially spaced transverse passages positioned therein, said passages being parallel to eachother and to the inner edge of said segment, said passages ,being alternately `large and small in each of `said segments, said passages being of large and small size in alternate segments on any transverse plane, and -a plurality of straps threaded `through said and contacting the periphery of said small passages and spaced from the periphery `or" said 'larger passages, so as to electrically Connect together' 4alternate segments of said assembled anode.

References Cited in the -le of Vthis patent UNlTED STATES PATENTS

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