US2429291A

US2429291A - Magnetron

Info

Publication number: US2429291A
Application number: US492995A
Authority: US
Inventors: Ernest C Okress
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1943-07-01
Filing date: 1943-07-01
Publication date: 1947-10-21
Anticipated expiration: 1964-10-21

Description

Oct. 21, 1947. Q OKRESS 2,429,291

MAGNETRON Filed July 1, 1943 2 Sheets-Sheet l INVENTOR E. c. o/rzfss ATTORNEY Patented Oct. 21, 1947 MAGNETRON Ernest C. ()kress, Montclair, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 1, 1943, Serial No. 492,995

. 11 Claims. (01. 315-) This invention relates to magnetrons and particularly to such devices in the ultra high frequency or so-called micro-wave range which, though not definitely defined, may be considered as certainly including wave-lengths up to one hundred centimeters.

Magnetrons as heretofore constructed have had a generally symmetrical arrangement of cavities, of which examples may be seen in my prior application, Serial No. 460,376, filed October 1, 1942, entitled Magnetron and method of manufacture, and assigned to the same assignee as the present application. The prior art, in its relation to the invention here disclosed, may be summarized as providing generally cylindrical central cavity for the cathode, and having a plurality of radiating cavities evenly spaced around and opening into the central cavity. An even number of radiating cavities constitute the multiplicity thereof used, and in quantity usually range from six to ten with eight radiating cavities most commonly employed. This prior art type of magnetron has serious disadvantages amongst. which may be mentioned the difficulty in fabrication of obtaining the requisite accuracy which has to be in some instances within 10.0005 of an inch. Manufacture is consequently expensive and involves many discarded magnetrons due to discrepancy from the permitted tolerance. It has also been found that the muJti-cavity magnetrons of the prior art promote oscillation or resonance in a plurality of modes rather than just a desired single mode. Strapping of alternate anode segments has been resorted to in the prior art in an eifort to overcome this undesirable behavior, but not with complete success, and in addition added electrical and mechanical difficulties are introduced,

The present invention has for it general object the purpose of presenting another means whereby such difliculties and deficiencies encountered in prior art magnetrons may be alleviated.

More specifically, an object of the invention is to overcome construction and operation productive of undesired modes of oscillation.

Another object of the invention is to simplify construction both to lessen the difilculty of satisfactory manufacture and cost and to reduce percentage of discards.

A further object of the invention is to enable th size of the magnetron for a given wave-length to be less than heretofore.

Again, an object of the invention is to provide a construction admitting of less critical tolerances without materially afiecting operation.

Still further objects will appear as the description proceeds, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views;

Figure 1 is a cross-sectional view, normal to the axes of the several cavities, of a magnetron constructed in accordance with my invention, as upon line II of Fig. 2; I

Figure 2 is a vertical section on a plane defined by the axes of the cathode cavity and of the input and output leads;

Figure 3 is a sectional view as on arcuate line III-III of Fig. 1 for purposes of showing graphically the magnetic field lines of force in the resonant cavities;

Figure 4 is a diagrammatic view similar in nature to Fig. 1 but graphically showing the E and H lines theoretically present in the cavities;

Figure 5 is a vertical sectional view similar to Fig. 2 and showing a construction modified as to output lead, the section being taken on a plane indicated by line VV of Fig. 6;

Figure 6 is a cross-sectional view on line VI-VI ing to Fig. 8 but modified as to character of cavity resonators and output coupling.

In the specific embodiment of the invention illustrated in said drawing and directing attention particularly to Figures 1 to 6 thereof, the reference numeral 15 designates a cylindrical magnetron body having end plates or covers 10 sealed thereto whereby the interior may be evacuated. The interior of said body is formed to comprise an anode ll of generally cylindrical shape, shorter than the body which has end flanges l8 for spacing the covers I6 from the ends of the anode and thereby afford the usual and necessary end spaces I9 within the magnetron.

The present showing of the magnetron preferably provides a cathode cavity 20 parallel to but offset from or eccentric with respect to the axis of the anode body and magnetron, said cavity extending through the anode so as to open into Likewise eccentric to the;

both end spaces l9.

3 anode axis and extending longitudinally through the anode to the end spaces l9 are a plurality of resonant cavities 2| which are otherwise separate from each other but open longitudinally at the side of the cathode cavity as by constriction 22 and constitute cavity resonators. In Figures 1 to 6, two cavity resonators 2i are shown of. generally cylindrical shape andwith distinct slot-- like constrictions 22 interposed between the cylindrical part of the cavities 2| and the oathode cavity 20. In Figure '7, two cavity resonators Zla are shown of slot-like formation and in continuation of the slot-like constrictions 22a, to

the cylindrical cathode cavity 20a and allwithin.

an anode I la of a magnetron otherwise substantially as described above. These two exemplifications illustrate the feature of eccentricity of.cathode cavities in an anode and with two cavity-res scribed-above. And, furthermore, the feature of eccentricity with a plurality, more than two, of slot-like cavity resonators maybe employed and is exemplified in Figure 10, wherein threeslotlike resonant cavities 210 are shown, the side walls of which are in continuation of the slot-like constrictions 220 to the cylindrical cathode cav= ity 200 shown eccentrically situated in an anode llc of a magnetron otherwise substantially as described above.

Consequently, in all forms of the invention shown, the cathodecavi-ty'is eccentric to and at one-side'of the axis of the anode body and the cavityresonators are at'an opposite side of the axis and a'constriction lengthwise of the cavities connects each cavity resonator with'thecathodecavity. Also in all forms of the invention, the ends of all cavities open into end spacesin the magnetron 4 body,

Otherstructurescommon to all forms of-the invention, and accordingly identified throughoutbythe same reference numerals, comprises a cathode 23 extending through the cathode cavitycoaxial therewith and into the end spaces of the illustrated magnetron. The cathode is supported at its ends by ceramic or other insulating collars 24 011- the outer ends of which are mounted metal discs 25 to which lead-in wires 2&arerad-ially attached. These lead-in wires are sealed through appropriate sealing means 21 for the purpose at the side of the magnetron. A heater filament 28 extends through the cathode and is attached at its ends to said discs 25.

An output connectionis made appropriately from within the magnetron.--

spacewith-symmetrical disposition of the cavity resonators on oppositesides of the output. this-instance, as shown in Figures 1 and 2, the

output 29 is a wire, the end of which is embedded inthe partition between two cavity resonators andnextthe cathode-cavity, said wire-at its embedded end portion being parallel to the axis of the cathode cavity and projecting away from the. end oi the anodeinto. the endj'space where. it'. bends at right angles and extends through the end In constructions having an even number ofcavi-tyresonators, the outputmay conveniently be situated inan-en-d- "in a middle one of the several cavities.

the three cavities.

= radius particularly by reducing thelatter:

space medially across said partition and out through the side wall of the magnetron through appropriate sealing means 30. It is, however, within the scope of the invention to otherwise situate and construct the output lead. For instance, as shown in Figures 5 and 6, the output lead 3] is introduced midway of the length of one cavity resonator 2i and in the form of a loop, the plane of which is transverse to the caviti axis. With use of an odd number of cavity resonators, it is convenient to situate the output lead For instance, in the showing of Figures 8 and 9, there are three cylindrical cavity resonators, and a looped output lead 3| as above described may also be used here and inserted in the middle one of In Figure 10 showing three slot-type cavity resonators, the output 32 may conveniently have the form of a probe entering the middle one of said slot cavities perpendicular thereto.

With magnetrons as here, disclosed in which more than two cavity resonators are employed, it is preferable'to strap alternate partitions to each other, and by way of illustration staple-like straps 33 made of wire are shown in Figures 8 and 9.

The field conditions existing in the cavity resonators are indicated in Fig. 4 wherein are shown E lines representative of the electric component of the electromagnetic field and circles representative of the H or magnetic component ofthe electromagnetic field. The direction of the flux-lines H isindicatedby theusual dot'and cross within the circles, the dot indicating direction toward the reader and the cross indicating direction-away from the reader. Conduction and displacement currents'fiow in accordance with Maxwellstheory, for the boundary'conditions imposed as indicated'in Figure 4;

Field'conditionsin the solid angle, 0: (see Fig. 4) are similar to those existing'in the symmetric form.- The 'D. C. fields required are higher, espe ially the cut-01f voltage. Both may be compensated by altering1both' the cathode and anode The dimensions of the resonator system do not materiallydepart from'the relations for themultiple cavity magnetron.

The dual cavity deviceoperateson thebu-nchercatcher principle. External coupling should'be madein the cavity which acts asacatcher as determined by the axial magnetic field-polarity; A three-cavitysystem should operate equally well witheitherdirection of theaxial magnetic field" with the coupling device in the cavity as shown in Figure 8.; Cross strapping as shown in thisfigurewill improve the efficiency of operation in the fundamental. .mode.

It isa factthata magnetron-constructed in accordance with the present invention-utilizing eccentric disposition of cavities and limited number of resonant cavities may be made much smaller than, the prior art conventional symmetrical magnetron. The" reduced number of cavities also" reduces manufacturing operationsand cost, and it has beenadvantageously ascertained that tolerances of dimensions are less.

1. A magnetronhavingan,anode. bodysub v stantially cylindrical about an axis, said body having cavities therein longitudinally parallel to each other and to said axis, said body completely surrounding said cavities, one cavity of said cavities being axially ofiset from the said axis of the body and all other of said cavities radiating from the said one cavity, and a cathode in said one cavity.

2. A magnetron having an anode body substantially cylindrical about an axis, said body having cavities therein longitudinally parallel to each other and to said axis, said body completely surrounding said cavities, one of said cavities being cylindrical and axially offset from the said axis of the body and constituting a cathode cavity, and all other of said cavities each radiating from the said cathode cavity, and a cathode in said one cavity.

3. A magnetron having an anode body substantially cylindrical about an axis, said body having cavities therein longitudinally parallel to each other and to said axis, said body completely surrounding said cavities, one of said cavities being cylindrical and axially ofiset from the said axis of the body and constituting a cathode cavity and all other of said cavities constituting cavity resonators and each radiating from the said cathode cavity and having a width perpendicular to direction of radiation less than the diameter of said cathode cavity, and a cathode in said cathode cavity. A

4. A magnetron having an anode body with a cathode cavity eccentrically disposed therein on one side of the middle of said body, and with cavity resonators eccentric to the anode body on an opposite side of the middle thereof and radiating from the cathode cavity, and a cathode in said cathode cavity.

5. A magnetron having an anode body with a cathode cavity eccentrically disposed therein on one side of the middle of said body, and dual cavity resonators eccentric to the anode body and both on an opposite side of the middle thereof and radiating from the cathode cavity, and a cathode in said cathode cavity.

6. A magnetron having an anode body with a cathode cavity eccentrically disposed therein on one side of the middle of said body, and more than two cavity resonators eccentric to the anode body, all of said cavity resonators being on an opposite side of the middle of the anode body and radiating from the cathode cavity, and a cathode in said cathode cavity.

'7. A magnetron having an anode body with a cathode cavity eccentrically disposed therein on one side of the middle of said body, and an odd number more than two of cavity resonators eccentric to the anode body, all of said cavity resonators being on an opposite side of the middle of the anode body and radiating from the cathode cavity, and a cathode in said cathode cavity.

3. A magnetron having an anode body with a cathode cavity eccentrically disposed therein and with an odd number only of evenly-spaced cavity resonators radiating from thereby providing one radiating cavity resonator symmetrically between other radiating cavity resonators, and an output lead partially in and extending from said one radiating cavity resonator symmetrically between other radiating cavity resonators.

9. A magnetron having an anode body with a cathode cavity eccentrically disposed therein entirely on one side of the middle of said body, and said body having only two cavity resonators of diverging slot formation radiating from said cathode cavity on an opposite side of the middle of said body.

10. A magnetron having an anode body with a cathode cavity eccentrically disposed therein entirely on one side of the middle of said body, said body having an odd number only of cylindrical cavity resonators on the opposite side of the middle of said body from the said cathode cavity,

and said cylindrical cavity resonators each having a slot connection with the cathode cavity.

11. A magnetron having an anode body with a cathode cavity eccentrically disposed therein entirely on one side of the middle of said body, said body having a total of only three slotlike cavity resonators radiating from said cathode cavity, and a probe-like output lead partially within and protruding laterally from the middle one of said cavity resonators.

ERNEST C. OKRESS.

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

UNITED STATES PATENTS Number Name Date 2,410,396 Spencer Oct. 29, 1946 2,408,237 Spencer Sept. 24, 1946 2,406,277 Bondley Aug. 20, 1946 2,408,234 Spencer Sept. 24, 1946 2,084,867 Prinz et a1 June 22, 1937 2,348,986 Linder May 16, 1944 2,075,855 Kilgore Apr. 16, 1937 2,071,311 Linder Feb. 16, 1937 2,115,521 Fritz et al Apr. 26, 1938 2,167,201 Dallenbach July 25, 1939 2,063,342 Samuel Dec. 8, 1936 FOREIGN PATENTS Number Country Date 215,600 Switzerland Oct. 16, 1941