US2444242A

US2444242A - Magnetron

Info

Publication number: US2444242A
Application number: US442345A
Authority: US
Inventors: John P Blewett
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1942-05-09
Filing date: 1942-05-09
Publication date: 1948-06-29
Anticipated expiration: 1965-06-29
Also published as: FR954568A

Description

June 29, 1948. Q J. P. BLEWETT IAGNETRON 2 Sheets-Sheet 1 Filed lay 9, 1942 Inventor- John F. Blewett, by W 6. JW W His Attorney- June 29, 1948. V'J. P. BLEWETT 2 Sheets-Sheet 2 Filed May 9, 1942 I I a I I r 1 i a o p r r a p I 1 Inventor-z 9 u: e n w W e O aim 9 A mM s H Patented June 29, 1948 MAGNETRON John P. Blewett, Scotla, N. Y., assignor to General Electric Company, acorporation of New York Application May 9, 1942, Serial No. 442,345

Claims.

The present invention relates to improvements in high frequency. electronic devices of the magnetron type.

A known type of magnetron employs a cylindrical array of mutually spaced anodes grouped about a centrally located emissive filament or cathode. The emitted electrons are subjected to a magnetic field and their resultant gyrations about. the cathode produce high frequency oscillatory voltages across the gaps separating the various anodes.

It is characteristic of magnetrons of this class that they tend to be somewhat unstable in operation. This is a result of the fact that at least certain of the electrons emitted from the cathode tend to return to the cathode with increased energy derived from the high frequency field which exists in the interelectrode space. The dissipation of this energy at the cathode surface raises the temperature of the cathode and increases its emissivity, this process being sometimes cumulative to such an extent that the cathode is destroyed. Even in cases where the cathode is not destroyed, the resultant variations in electron current causean objectionable change in the properties of the magnetron as a whole.

It is an object of the present invention to provide a multianode magnetron device which is essentially free of the undesirable qualities described in the foregoing. In general, this is accomplished by the provision of a cathode struc-- ture of such form that the emissive component is exposed to insufiicient bombardment materially to affect its emitting properties. As will be explained more fully at a later point, a particular cathode construction which serves this purpose has the further advantage of raising the operating eillciency of the magnetron as a whole.

The features of the invention desired to be protected herein are pointed out with particularity in the appended claims. The invention, itself, may best be understood by reference to the following description taken in connection with the drawings, in which Fig. l is a longitudinal section of a magnetron device suitably embodying the invention; Fig. 2 is a {850M011 taken on line 2--2 of Fig. 1; Fig. 3 is a fragmentary view illustrating in detail the construction of a portion of the cathode of Fig. 1; Fig. 4 isa schematic external view of the device of Fig. 1 and serves to illustrate the circuit connections for the device; Fig. 5 is a sectional view of a modified application of the-invention; and Fig.

6 is a section in another plane of the device of Fig. 5.

Referring particularly to Fig. 1, there is shown a magnetron device which comprises an elongated cylindrical envelope l0 constituted of glass. This includes an anode structure comprising two semi-cylindrical metallic elements l2 and I3 whichare arranged in opposed relation so as to provide a cylindrical array. As is shown most clearly in Fig. 2, elements l2 and I2 are mutually spaced to provide gaps I4 and I5 between them and are respectfully supported by conductors l6 and H which extend through the extremity of the envelope l0. 7

Within the anode structure there is provided a cathode assembly which in the first instance includes a pair of flanged, semi-cylindrical conductive (e. g. metallic) parts l8 and I! which conform generally to the shape and disposition of the anode elements [2 and I3. The parts I and H are respectively supported by

conductors

22 and 23 which extend through the lower extremity of the envelope Ill.

The conductive cathode parts it and I! are mutually spaced to provide gaps 25 and 28 between them and in these gaps there are located electron

emissive filaments

28 and 29 arranged in parallelism with one another. The filaments are joinedv at one extremity by means of a conductive cross-bar 3| and at their opposite extremities are associated with lead-in conductors 34 and 3S sealed into a stem press 36 (Fig. 3). Tension is applied to each filament by means of coil springs 31. 38, respectively, connected between the filaments and their associated leadin conductors. A center tap connection for the filament combination is provided by means of a conductor 40 which is joined to the cross-bar 3| and which is also sealed through the stem press 36.

The circuit connections of the various electrode elements so far referred to are indicated in Fig. 4. As appears in this figure, heating current is supplied to the

filament conductors

34 and 35 by means of a battery 46 connected between them. The center point of the battery which has its positive terminal connected to av conductive cross bar. 5| extending between the externally projecting portions of the conductors l8 and il. By this means a unidirectional electric field is established between the cathode assembly and the anode structure.

In the operation of the device a magnetic field is produced parallel to the various interelectrode gaps by means of a coil 55 which surrounds the envelope ill in a region coextensive with the electrode system. This coil is energized by the, application of a unidirectional potential.

As a result of the combined action of the magnetic field and the electrostatic field produced between the anode elements and the cathode assembly the electrons emitted by the

heated filaments

28 and 29 move orbitally around the oathode assembly 30 as to form a rotating space charge in the interelectrode space. As a con- 1 sequence of the electron gyrations, high frequency potentials are developed between the anode elements l2 and I3, that is. across the gaps which separate these elements.

The frequency of the oscillating voltage thus obtained may be controlled by proper adJustment of the circuit means interconnecting the anode elements. In the illustrated construction, this may be done by adjusting the location of the cross bar 5| (Fig. 4) to cause the conductors l6 and I! to function as a quarter-wave transmission line shortened by the interelectrode capacity and resonant at the desired frequency of operation.

- As a result of the adoption of a cathode construction of the type illustrated, only a minor proportion of the electrons emitted from the

filaments

28 and 29 are able to return to these filaments, the greater number of the reversed electrons being intercepted by the semicylindrical parts I! and i9. Due to the relatively extensive surface area of these parts and due further to the fact that they are not normally maintained at an emissive temperature, their bombardment does not affect the total electron supply and consequently does not produce any tendency for a runaway action to occur. On the contrary, even under relatively adverse operating conditions, these parts can still run well below an emitting temperature so that the cathode assembly as a whole may be regarded as an inherently stable system.

An improvement in the efliclency of the device as a whole can be realized by connecting the cathode parts l8 and IS in such fashion that they are adapted to follow the oscillations of the anode elements l2 and I3. This maybe accomplished for example, by locating the shortcircuiting conductor 49 (Fig. 4) at such a place that the combined eifect of the cathode and anode circuits is to produce resonance at the 9, 1 942, now Patent 2,428,612, issued October '7. 194

In this case the operating elements of thedevice are enclosed within a cylindrical metal container 80 and include a cathode assembly made up of an activated filament ii and a flanged plate i2, theiilament and plate being directly connected as indicated at N in Fig. 8. A collector 85 for the electrons emitted by the filament is provided at one end of the cathode assembly. being connected to an anode structure to be described in the following. A series of eyelet seals 86 are provided for the purpose of supplying potential to the various electrode elements enclosed by the container 80.

The anode structure is formed of a unitary rectangular block ll of conductive metal such as copper and is provided at the edge which faces the cathode assembly with a series of mutually displaced slots 10 to 13. These serve the double function of dividing the structure into a series of independent anode elements and of providing space resonant cavities between adiacent elements. These cavities, which are defined by the opposed metallic surfaces of the high frequency alternating voltages may be developed between the adjacent anode elements. The various resonant systems thus provided are inherently coupled to one another so that their action is mutually reinforced.

In order to obtain resonance effects of the desired character electrons are supplied to the space between the cathode plate 2 and the anode structure by the emissive filament II which lies in a semi-cylindrical depression provided near one extremity of the plate 82. A unidirectional potential is impressed between the cathode and anode structures from an external source (not shown) and a magnetic field parallel to the gaps 10 to I3 is provided by an external magnet having poles l5 and 18 (Fig. 6).

ment taken from a cylindrical multi-anode magnetronof infinite diameter. That is to-say. the gyrations of the electrons emitted fromthefilament 6| as they'pass in proximity to the various desired operating frequency. The two cathode parts are respectively sufilciently well coupled to the corresponding anode elements so that with this arrangement they will oscillate in phase with these elements. There will then be no high anode elements excite the elements in the manner characteristic of magnetron operation. Insofar as the present invention is concerned the arrangement has the advantage attributed to the construction of Fig. 1 that the cathode is incapable of runaway operation, so that the functioning of the device as a whole is inherently stable.

In order to take power from the device of Fig. 5, use can be made of a coupling loop 19 which is terminally connected to the anode structure as indicated at 8.0 and which is brought out through the wall of the container '60 through a conductive tube (e. g. a transmission line) illustrated at 82. A glass bead 83 sealed into the tube preserves the v acuum within the container.

While the invention has been described by reference to particular embodiments it will be understood that numerous modifications may be made by those skilled in the art without depart variations as come within the true spirit and scope of the ioregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A magnetron device comprising an anode tron emissive element in said gap, and magneticmeans adjacent said structure for producing a magnetic field in the space between the said anode structure and the said cathode assembly and in a direction'parallel to said gaps.

2. A magnetron device comprising an anode structure includingan array of anode elements which are mutually spaced apart providing gaps between them, a cathode system adjacent to the said anode structure comprising a plurality of I spaced conductive parts which correspond in number and arrangement to the said anode elements, means included in said cathode system for supplying electrons to the space between said anode elements and said conductive parts, means resonant at'a desired operating frequency inter connecting the anode elements, and means interconnecting the said conductive parts and resonant at'said frequency.

3. A magnetron device comprising an anode structure including an array oi. anode elements which are mutually spaced providing gaps between them, a conductive structure having a surface opposed to said anode structure and conarray, said conductive structure being divided into spaced parts which correspond in number .be maintained at the same direct current potential as said conductive structure during op-' eration oi the device, means interconnectin the said anode elements, and further means interconnecting the said conductive parts, both a forming approximately to the shape of said said interconnecting means being resonant at a desired operating frequency.

4. An electron discharge device of the magnetron type comprising spaced anode elements defining a plurality of mutually parallel gap therebetween, a cathode assembly comprising a conductive structure opposed to said anode elements and having a surface substantially coextensive with the said elements, said structure" having an opening parallel to and substantially coextensive with the longitudinal dimension of said gaps, and an elongated thermionically emissive filament within said opening constituting an electron emisive source parallel to and coextensive with the longitudinal dimension of said gaps for supplying electrons to the space between said structure and said anode elements, said filament constituting a component of the said-cathode assembly but providing only a minor fraction of the-total area thereof, and magnetic means adJ'acent said structureto produce a magnetic field in the space between said anode elements and cathode assembly in a direction parallel to said gum 5. An electron discharge device of the magnetron type comprising an anode structure including a plurality of mutually spaced anode elements defining a plurality of mutually parallel gaps therebetween, a cathode assembly comprising a conductive structure opposed to said anode elements and having a surface substantially parallel to and coextensive with said anode elements, and an elongated thermionically emissive cathode element adjacent said member parallel to and substantially coextensive with the longitudinal dimension of said gaps for supplying electrons to the space between said conductive structure and said elements, said anode elements, said conductive structure and said cathode element being substantially coextensive in length and said cathode element being of small area compared to the area of said conductive structure whereby a substantial proportion of electrons returning from said anode elements to said cathode assembly may-be intercepted by said conductive structure and-thereby prevented from bombarding said cathode element, and magnetic means adjacent said structure to produce a magnetic fleld in the space between said anode elements and cathode assembly in a direction parallel to said gaps.

JOHN P. BLEWETT.

' REFERENCES CITED The following references are of record in the file of this patent: I

' UNITED STATES PATENTS- Number Name Date 1,791,973 Perryman Feb. 10,1931 2,073,599 Malter March 9, 1937 2,096,817 Malter et a1 Oct. 26, 1937 2,143,146 Farnsworth et a1. Jan. 10, 1939 2,151,766 Hollmann March 28, 1939 2,157,585 Zworykin May 9, 1939 2,158,114 Fritz May 16, 1939 2,233,779 Fritz March 4, 1941 2,235,517 Espe March 18, 1941 2,288,812 Linder July 7, 1942 2,400,770 Mouromtseil et a1. May 21, 1946 FOREIGN PATENTS Number Country Date Australia Feb. 9, 193a