US2651003A

US2651003A - Magnetron

Info

Publication number: US2651003A
Application number: US299774A
Authority: US
Inventors: Greenwald Sylvia
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-07-10
Filing date: 1952-07-10
Publication date: 1953-09-01
Anticipated expiration: 1970-09-01

Description

Sept 1, 1953 GREENWALD 2,651,003

` MAGNETRON Filed July 1o, 1952 Illl #VVE/V701?, LEWIS GREENWALD, deceqsed #or-nes by sYLvIA GREENWALD, udmimsfmmx.

Patented Sept. 1, 1953 UNITED STATES PATENT OFFICE MAGNETRON v the Army Application July 10, 1952, Serial No. 299,774

8 Claims. (Cl. 315-40) (Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without payment of any royalty thereon.

This invention relates to microwave oscillators and more particularly to interdigital type magnetrons.

It is well known that although the pill-box cavity interdigital magnetron resonates at a single desired frequency, there are present higher modes of oscillation outside the desired resonant frequency range. Heretofore, interdigital magnetrons of this type have been limited to the cavity or zero-order mode of operation because in this mode the tooth structure presents an uncontaminated vr-mode field configuration to the interaction space, thus providing relatively high power output and eiciency. When such interdigital magnetrons are operated at frequencies in higher modes than the cavity mode, it has been found that the power output and eiliciency is substantially decreased. The reason for this is probably that the interdigital magnetron structure does not present a field distribution to the electrons which permits eilicient conversion to radio frequency power at the higher modes.

It is therefore an object of this invention to provide an interdigital magnetron structure which will permit efficient operation at modes higher than the cavity mode.

Another object of this invention is to provide an interdigital magnetron structure which will permit 1r-mode operation for modes higher than the cavity or zero-order mode.

It is yet another object of this invention to provide a single cavity interdigital magnetron having concentric interleaving sets of teeth for eiiciently utilizing the higher modes of oscillation.

In accordance with the present invention, the interdigital magnetron structure includes a hollow cavity resonator terminated by a cylindrical wall and a pair of upper and lower spaced annular end plates. There is also includes an axial cathode, a first set of interleaving teeth circumferentially disposed about said cathode comprising one series of alternate teeth depending from the inner periphery of said upper annular plate and another series of alternate teeth depending from the inner periphery of said lower annular plate. A second set of interleaving teeth cornprising two series of alternate teeth having discrete spaced supporting means is circumferentially disposed within said first set of interleaving teeth and is concentrically arranged therefwith. Also included are means for coupling said second set of teeth to said first set of teeth whereby the second set of interleaving teeth presents a wmode distribution to the electron space charge at a preselected higher mode of oscillation.

For a better understanding of the present in= vention, together with other and further objects thereof, reference is had to the following description taken in connection with the accom panying drawing, in which:

Fig. 1 is a perspective view, partly in section, illustrating the magnetron structure embodied in the present invention; and

Fig. 2 is a transverse sectional View, taken on line 2-2 of Fig. 1, and illustrates the sinusoidal radio frequency field variation of a 3rd-order mode of oscillation around the cavity anode.

Referring now to Figs. 1 and 2 of the draw-v ing, there is shown an electron discharge device magnetron comprising an evacuated cavity resonator 3 having a cylindrical wall 5 terminated by spaced annular upper and lower end plates 4 and 6, respectively, which are axially aligned. A first set of uniformly spaced interleaving teeth l and Ill is concentrically arranged about the axis of cavity resonator 3 at the inner peripheries of said annular end plates to form a cavity anode 8. Alternate cavity teeth lil extend downwardly from upper ring l2 which is affixed to upper end plate Il. The other alternate cavity teeth I4 extend upwardly from lower ring r6 which is afxed to lower end plate 6, so that, if one goes around the cavity anode in any one direction, alternate teeth are joined to the same annular end plate. Thus, cavity anode 8 comprises a plurality of oppositely placed sets of uniformly spaced teeth extending toward each other from the inner periphery of said annular end plates. Each of these teeth are of uniform length and width, the length of the teeth being approximately equal to the spacing between said annular end plates. A cathode is is axially and centrally positioned within cavity resonator 3 and may be supported in the usual manner. The usual magnetic and electric field between cavity anode 8 and axial cathode I8 may be provided in the conventional manner to produce an interaction electron space charge therebetween. Although twelve teeth are shown, it is to be understood that the interdigital magnetron is essentially a single cavity resonator and that the number1 of modes is not primarily dependent on the number of cavity teeth.

The interdigital cavity anode described hereinabove is well known in the art. The modes which may exist in such a cavity anode when excited by a high radio frequency field is described by Joseph F. Hull and Arthur W. Randalls in the Proceedings of the Institute of Radio Engineers, November 1948, pp. 1357-1363. The lowest order mode which may exist is known as the cavity Inode or zero-order mode in which there is a 180 phase difference between adjacent cavity anode teeth. It has been determined that the field and current distribution of the NIch order mode have N sinusoidal variations around the circumference of the cavity anode, and, accordingly, the amplitudes of the radio frequency fields for a preselected mode varies sinusoidally around cavity teeth 8. Thus, the voltage distribution between adjacent teeth will also vary sinusoidally. For example, if the 3rd-order mode of operation is considered, the amplitude of the radio frequency fields and, hence, the voltage distribution between adjacent teeth, will vary sinusoidally around cavity anode 8 making three complete cycles, This is clearly shown in Fig. 2, wherein the solid line indicates the sinusoidal variation of the radio frequency potential existing on alternate cavity teeth I8 and the dashed line indicates the sinusoidal variation of the radio frequency potential existing on the other alternate cavity teeth i4. As shown in Fig. 2, there is a 180 phase relationship between the sinusoidal variations.

In accordance with the present invention, a second set of uniformly spaced interleaving

teeth

24 and 25 is concentrically arranged about cathode I8 and radially spaced from cavity anode [i to form an inner anode 20. Alternate teeth 22 of said inner anode extend downwardly fromL ring 24 which is coplanar with upper ring l2. To other alternate inner anode teeth 25 extend upwardly from ring 28 is coplanar with ring i8. Thus, if one goes around the inner anode in any one direction, alternate teeth are joined to the same ring. Each of the inner anode teeth are of uniform length and width, the length of the teeth being approximately equal to the spacing between

rings

24 and 26. Cavity anode 8 is spaced from inner anode 20 and supported in position by means of symmetrically disposed triangular shaped tabs 30, extendingr radially from

rings

24 and 26. These tabs couple the radio frequency fields excited along the inner anode to drive the cavity anode in the preselected mode. Inner anode 20 is so positioned with respect to cavity anode 8 that the apices of the tabs 38 are attached to cavity anode 8 at points of equal potential for the selected higher order mode of oscillation, preferably at points of maximum amplitude potential. As shown, the tabs respectively aiiixed to

rings

24 and 26 are linearly aligned so that there is a 180 phase relation between oscillations of adjacent teeth of inner anode 28. It is to be understood, of course, that the number of tabs extending radially from each of the rings 24 and 28 is a function of the higher mode of operation. For example, if the 3rdorder mode operation is desired, then three symmetrically disposed tabs will extend radially from ring 24 and connect to ring I2 and three similarly disposed tabs will connect ring 28 to ring I6. Thus, for the 3rd-order mode of operation the electrons in the interaction space move in fields similar to those encountered in the usual qr-mode operation.

In operation, the electron space charge sweeping past the inner anode teeth 20 induces voltages therebetween to excite high frequency elds in the cavity anode. Since the inner anode presents a vr-mode potential distribution to the electron space charge for the preselected higher mode of operation, the coupling tabs 3D will drive the cavity anode 8 in the preselected mode of operation. Thus, one larger cavity may be used to obtain higher frequencies by utilizing the higher modes of oscillation of such a cavity, while at the same time using a magnetron interaction space capable of exciting the cavity in an efficient manner. When the magnetron oscillates at the selected higher mode, the teeth Aof cavity anode 8 provide the necessary shielding between inner anode 28 and the cavity resonator 3.

The addition of the inner anode 28 may add capacity to the cavity anode 8 at points where 'the tabs 38 connect thereto. Ihis may be overcome by increasing the spacing between ends of the interleaving cavity anode teeth adjacent said tabs so that the capacity of the teeth of inner anode 20, when added to the capacity of the cavity anode teeth, restores an even distribution of the capacity loading of cavity resonator 3.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those `skilled in the art that various changes and modifications may be made therein, without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit .and scope of the invention.

What is claimed is:

1. A hollow cavity resonator having an outer cylindrical wall connected to upper and lower annular plates; a cathode axially and centrally positioned within said resonator; a first set of interleaving teeth comprising one series of alternate teeth depending from the inner periphery of said upper plate and a second series of alternate teeth extending from the inner periphery of said lower plate; a second set of interleaving teeth circumferentially disposed within said first set of teeth and concentric therewith, said second set of teeth comprising two series of alternate teeth, each alternate series of said second .set of teeth having discrete supporting means; and means connecting said second set of teeth to said first set of teeth whereby said second set of interleaving teeth presents a 1r-mode distribution to the electron space charge from said cathode at a preselected higher mode of oscillations.

2. The device set forth in claim 1 wherein said last mentioned means comprises a plurality of symmetrically disposed tabs extending radially from said supporting means, the number of said tabs extending radially from each of said supporting means being equal in number to said preselected higher mode of oscillation.

3. A hollow cavity resonator having a cylindrical wall; a cathode axially and centrally positioned within said resonator; a cavity anode comprising two series of alternate teeth circumferentially disposed about said cathode forming a first set of interleaving teeth, each alternate series of teeth having discrete axially spaced outer supporting means affixed to said wall; an inner anode comprising two series of alternate teeth circumferentially disposed about said cathode forming a second set of interleaving teeth, each alternate series of said inner anode teeth having ldiscrete axiallyv spaced inner supporting means, said second set of teeth being within said rst set of teeth and concentric therewith; a first and second group of symmetrically disposed tabs extending radially from said inner supporting means to said outer supporting means, said tabs being axially aligned and connected to said outer supoprting means at points of equal potential at a preselected higher mode of oscillation.

4. A hollow cavity resonator comprising a cavity anode, said anode comprising two series of alternate teeth circumferentially disposed forming a iirst set of interleaving teeth, each alternate series oi teeth having discrete axially spaced outer supporting means; an inner anode comprising two series of alternate teeth circumferentially disposed forming a second set of interleaving teeth, each alternate series of said inner anode teeth having discrete axially spaced inner supporting means, said second set of teeth being within said first set of teeth and concentrically arranged therewith; a first group of symmetrically disposed tabs extending radially from one of said inner supporting means and connecting one alternate series of said rst set of interleaving teeth and one alternate series of said second set of interleaving teeth; and a second group of symmetrically disposed tabs extending radially from the other inner supporting means and connecting the other alternate series of said first set of interleaving teeth to the other alternate series of said second set of interleaving teeth; the tabs in said groups being linearly aligned and the number of tabs in each group being equal in number to a preselected higher mode of oscillation.

5. A hollow cavity resonator having an outer cylindrical wall connected by upper and lower axially spaced annular plates; an outer anode comprising two series of alternate teeth circumferentially disposed on the inner periphery of said plates forming a rst set of interleaving teeth, one series of alternate teeth extending upwardly from said lower plate and the other series of alternate teeth extending downwardly from said upper plate; an inner anode comprising a pair of upper and lower axially spaced supporting rings, two series of alternate teeth circumferentially disposed on said supporting rings forming a second set of interleaving teeth within said outer anode and concentrically arranged therewith, one alternate series of said inner anode teeth extending downwardly from said upper supporting ring, the other alternate series of said inner anode teeth extending upwardly from said lower supporting ring; a first group of symmetrically disposed tabs extending radially from said upper supporting ring to said upper annular plate; and a second group of symmetrically disposed tabs extending radially from said lower supporting ring to said lower annular plate, said tabs being linearly aligned and the number of tabs in each of said groups being equal in number to a preselected higher mode of oscillation.

6. The device set forth in claim 5 wherein said upper and lower annular plates are respectively coplanar with said upper and lower supporting rings.

7. A hollow cavity resonator having a cylindrical wall connected by upper and lower axially spaced annular plates; an outer anode comprising two series of alternate teeth circumferentially disposed on the inner peripheries of said plates forming a rst set of interleaving teeth, one series of alternate teeth extending upwardly from said lower plate and the other series of alternate teeth extending downwardly from said upper plate; an inner anode comprising a pair of upper and lower axially spaced supporting rings, two series of alternate teeth circumferentially disposed on said supporting means forming a second set of interleaving teeth within said outer anode and concentric therewith, one alternate series of said inner anode teeth extending downwardly from said upper supporting ring, the other alternate series of said inner anode teeth extending upwardly from said lower supporting ring, a rst group of symmetrically disposed tabs extending radially from said upper supporting ring to said upper annular plate; and a second group of symmetrically disposed tabs extending radially from said lower supporting ring to said lower annular plate, said tabs being linearly aligned and connected to points of equal potentials on said outer anode.

8. A hollow cavity resonator comprising a iirst set of circumferentially disposed interdigital teeth; a cathode axially and centrally positioned within said first set of teeth; a second set of circumferentially disposed interdigital teeth within said first set of teeth and concentric therewith; and means extending radially from said second set of teeth and connecting to said rst set of teeth whereby said second set of teeth presents a fr-mode distribution to the electron space charge from said cathode at a preselected higher mode of oscillation.

SYLVIA GREENWALD, Administratrz'x of the estate of Lewis Greenwald, deceased.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,525,721A Posthumus Oct. 10, 1950 2,597,506 Ludi May 20, 1952