US2408235A

US2408235A - High efficiency magnetron

Info

Publication number: US2408235A
Application number: US425071A
Authority: US
Inventors: Percy L Spencer
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1941-12-31
Filing date: 1941-12-31
Publication date: 1946-09-24
Anticipated expiration: 1963-09-24

Description

Sel- 24,1945 I P. L. SPENCER l* 2,408,235 v HIGH EFFICIENCY MAGNETRON v Filfed Dee. 31, 1941 2 Sheets-Sheet l @fw-fw f Patented Sept. 24,` 1946 2,408,235 HIGH EFFICIENCYMAGNETRON Application December 31, 1941, Serial No. 425,071

1o claims. (C1. 25o-27.5)

`..This` invention vrelates to a magnetron, and n moreparticularly to one which has a plurality of possible oscillating modes, `each .determined prilInarily by the geometry of theinternal structure of'. the magnetron. A device of this kind is intended to oscillate in a predetermined principal mode so as to generate a predetermined frequency. Heretofore the existence of additional modes of oscillation have introduced serious dificul-ties. Such additional modes Vhave caused spurious oscillations to be generated, thus consuming energy which reduced the eiciency and effectiveness of the device. f

Anv object of this invention is substantially to eliminate the undesired character of the additional or spurious modes offoscillation by utilizing them toV reinforce the principal or normal os- `cillator mode of a magnetron.

Another object is to provide means for tuning one mode of oscillation independent of another so as to bring both modes into synchronism.

A further object is .to increase the eiiiciency and `effectiveness of a magnetron of theforegoing type..

The foregoing and other objects of this invention willrbe best understood from the following vdescription of an exemplii'lcation thereof, reference being had to .the accompanying drawings, wherein:

Fig. 1 is a transverse section of a magnetron v4This block forms the anode of the magnetron.

iThe' block has hollow end sections which are. covered by caps 2 and 3, likewise of .conductive material such as copper. Between the hollow end sections of the block I is located a central bridging portion 4. The portion 4 is provided with a central bore 5 within which is supported substantially at the center thereof a Acathode 6 which may be of the indirectly-heated oxide-coated thermionic type. The cathode is supported by a pair of cathode lead-in conductors 1 and 8 sealed through glass seals 9 and I0 mounted at the outer ends of pipes II and I2 hermetically fastened within .the walls of the block I'adjacent the upper and lower hollow end sections. A plurality of slots I3 extend radially from the central bore 5,

opening I4 rextending through the bridging portion 4. In this way the anode structure is provided wth a plurality of wedge-shaped arms I5 anode sections with the cathode 6.

2 1 .Y to r22, inclusive, the faces of which cooperate as `Whenfsuch a magnetron isy placedrbetween suitable,magneticfpoles -23 and 24 to create a longitudinalmagneticfield and the device is energized, oscillations are set up. These oscillations maybe led out from the tube by means of a cou-A mounted at theV outer end of a pipe 28 likewise hermetically fastened through the wall of the envelope I. -An additional conducting pipe,v not shown,v may be electrically connected ,to the pipe 28,- and forms with the wire 26 a concentric line through which the high frequency oscillations generated by the magnetron may be conducted to a suitable utilization circuit. v A

A capacity exists between .the cathode 6 and the face of each of the anodesections I 522.V Also capacitances'exist between the side walls of each of the slots I3.' The inner walls of the. openings .I4 constitute inductances. The anode, therefore,

is so designed and spaced relative to the cathode that the inductances and the ,capacitan-ces. de-

scribed constitutey circuits which are tuned, and thus are resonantat a vpredetermined frequency .at which the device is to be operated. The device -is intended tooperate so 4that each b ore I4 andv Yits adjacent arms form a circuit tuned to the frequency.l at which each of the'other bores I4 fand each of said slots terminates in a rcircular yundesired spurious modes. i vtroublesome mode is that. in which alternate anode arms form opposite ends of an oscillating circuit extendingaround the back of a pair of openings I4. -As more fully described and claimed in my copending application, Serial No. 421,145, led- December l, 1941, this spurious oscillating mode can be substantially eliminated by inter.- conneoting the `outer ends of alternate anode arms directly `by relatively low impedance paths. In the arrangement as shown herein, such interconnection is made in somewhat different manner from that shown in my said copending application. As shown in Fig..1, a conductorr 29, preferably of copper, is fastened to and interconnects the anode arms 2| and I9. Also a simi- .lar conductor 30 interconnects anode arms I6 and i8. vThese two connections are made at one end,

vfor example the upper'end of the magnetron structure.

At the other end of the structure a conductor lfpreferably of copper, is connected to and interconnects ranode arms I5, I'I and I9, while'a similar conductor 32 interconnects anode 3

arms

22, 20 and I8. The conductors 3l and 32 overlap, at yone.sicle of the structure, leavinga gap at zthe.: otherisidefof said structure along which the conductor 8 may extend. Similarly at the other end of the structure conductors `2S and 3% leave a gap through which the conductor I may extend. In this way theseinterconnecting conductors may extend beyond the end of the bridging member 4 without interferingwithiithe lead-in conductors 'l and`8, respectively, ;Like;

wise a gap between the other ends of the

conductors

29 and 30, as shown iniFig. 1,.formszafgap permitting an arm 34, the purpose ofwhichwill be described below, to extend along said gap without interference. As will be seen most clearly *frm-@Figs 4; the interconnections fdescribefd, above interconnect -al-ter-nate' v:anode yarms ydirectly 'through relatively vlow impedance -fcon'ductive \'paths, 'thus substantially-feliminatingthe spurious 'oscillating-mode described above. "'Therefore'f the anode'- 'structure' will#oscillate-Wv'ithj each .boref il 4 'and the adjacenty anode u*armsf'iorminga tuned circuit'- as'` describedAl above. "'fThis Inode A'of' oscilla- 'tion'can :be termed' the""transverse mo'de.

v1`Ons-referringtoFig.y 4lit will be vseen that'a path'A exists ifromfthe `uppe1'=en"d ffano'de face v22 -to thelowerf'erid; valong theconductor' 32 tothe 'loweren'd f-anode face 2U,-an'd thencei'fto'the upper ierdl thereof. `TThis ycircuit contains i an apv-preciable amountof -i-nductanceand'some capacitance. I `have found that undertpropercondi- 'tionsjthedeviee cani be made" to 'oscillate' ener- Afgeticallya'longfsuch a path. Thus the pathtraced can` be made an. oscillating modefvvhich 'may be termed a longitudinal )mode of oscillation Similar-"oscillating circuits exist respectivelyfibe- 'tween anode faces 2 I and' I 9,1"2 0 and "I 8, iiand vI l, llland 16; arid Il andl`5. 'f It will'be -notedthat 'all 'of' i;he 2'1.bove 'longitudinali oscillating paths are (3f-substantially; theL samellength' and curing-uration* so that thefrequencies' of oscillations in" this mode* are 'substantially equal. The@ frequency' of these oscillations 'thus produced is determined primarilyby the-length of: the 'ano'dei-facesf I 5422.

The frequencyf these oscillations linl'fhelongimoldes: are'stronglyA energized and reinforceea'ch u Lother. Intubes which'havebuilt in'accordance -withthis invention,I havefoun'd that the total lengthof each' longitudinal mode of oscillation is approximately equal toene-half of `a; VWave length fthe*desiredoscillationsigenerated by the magnetr'on.

"It is often'diiicult,topredeterminethev dimensionsv of'the structure exactly so as to make the longitudinal and oscillatingmodes of exactly the same frequency. Therefore it isf desirable to providemeans "for bringing these two modes of oscillation 'into exactA` synchronism. For example; a tuning arrangement as described andclaimed 'in my copending application," Serial No. 420,558, `filed November" 26; 1941, may be Iutilized ingorder 'tovary'theinductance of the `transverse oscillatingmodefor tuningy 'that mode. This tuning may .be carriedV out without" substantially affecting the frequency of the longitudinal mode. I prefer,

however. toy accomplish this; independent tuning mode.

by an arrangement as illustrated herein. I have found. that `a rconductingbody..heldiadiacent the anode; arms I5-22 affects the :icapacity of the circuit involved in the transverse oscillating Varying the position of this conducting body will vary this capacity While aiecting the .constants-ofthe longitudinal mode in a very much lesser degree. For the purposes of this device,

thegeffectj of ,this variation on the longitudinal .modelmay'be considered as substantially zero.

In order to produce this type of tuning, a light adjacent the anode arms I5-22 at one side of the structure. The ring 33 is split adjacent the leadin conductor i so as to leave a gap permittingadjfjustrnent o'f'the #ring 33f 'in Aa Lvertical*direction :withouty 'inter-ferenceL byg' said' conductor I'L V"The ring-33 may besuppytedsby aasupportingarm. which is bent' hfmg'h"S'u'bsiantiallyl might angie. and extends toy an'd isfsupportedbyanutt'. *The nut T35 isVV carriedatthe outer' end da pipe^^36 likewise hermeticallyf sealed through Y ther Wall of the envelope l. The pipe 36'- isprovidedrwith'a thinned section 31.

"When itis desired to adjust' thepositioniof 'the ring 33' relatively tof the anodel armsfa to'ol 'may be applied to the' nut35 so as4 to twistthe thinned section 31. This twistingfis' suicienttolgive `a permanent setto the'section" '31' to' Whatever 'position the nuty 35*v is turned. Inf thistway" the" ring 33 can be' held in-'any-fdenitedesired'position relative to the anode'arms within the `tuning limits of the device, rThefrequency of 4the'trans- Verse oscillating `Inode can 'betuned'so'as to bring it into exact synchronismJ with-the 'freabove,,a"verysremarkable"increase in ,the eiliciency of the'device results. "I'have"fc,und, for example, that the useful oscillatory powerin a deviceofthis-kindA canreadilyl be Ymade of v"the orderY of ,sixty per cent.' of the'total'en'ergy' input 'to the tube. lThis is anv extraordinarily high eiiiciency as comparedwith'those.efciences heretofore 'obtainable in; devices ofthiskind.

Qf courseltit' is to4 be .understood that thislinvention ',is not`l 'limited' to the'. particular .details `asfdescribed above as'many. equivalents, will suggest themselves .to those 'skilled' inlthe art. LFor "example, other anode congurations ,couldlbe utilized inpvvhich a plurality. of oscillating modes might Vbeposs'ible. ln. each instance a tuning of .various oscillatingmodes into .synchronism with eachother ,by any suitable tuning .means will result in relatively/high efficiencyifsthe principles of myinventionA are followed.

YWhat is claimed is:

l. vAn electron'discharge device Vcomprising. an ,electrode structure including Aacathode andn an anode, .said electrode... structurelhaving. a cong- .uration constituting capacitance and. inductance elements forming. circuits .whichare adapted ,to .have .osc'zillationssetY uprr therein.. saidoscillations being .all of the ,.same frequency,V a, plurality of predetermined points y on 4.said velectrode,,structure atwhichin-phase voltageloops of saidoscillations occur, andrelatiizely low .impedance .means directly interconnectingsaid .pointsand forming with portions of said electrode structure an additional oscillating circuit, the `frequency of said last-named oscillating circuit being substantially equal to the frequency of said firstnamed oscillating circuits.

2. An electron discharge device comprising a cathode and an anode, said anode having a plurality of electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate at a first frequency, relatively low impedance means directly interconnecting alternate electron-receiving portions, each pair of electron-receiving portions ,thus interconnected forming a tuned circuit adapted to oscillate at a second frequency, said second frequency being substantially equal to said first frequency.

3. An electron discharge device comprising a cathode and an anode, said anode having a plurality of electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate at a first frequency, relatively low impedance means directly interconnecting alternate electron-receiving portions, each pair of 4. A magnetron comprising an electrode structure including a cathode and an anode, means for producing a magnetic eld about said cathode, said electrode structure having a configuration constituting capacitance and inductance elements forming circuits which are adapted to have oscillations set up therein, said oscillations being all of the same frequency, a plurality of predetermined points4 on said electrode structure at which in-phase voltage loops of said oscillations occur, and relatively low impedance means directly interconnecting said points and forming with portions of said electrode structure an additional oscillating circuit, the frequency of said last-named oscillating circuit being substantially equal to the frequency of said firstnamed oscillating circuit.

5. A magnetron comprising acathode and an anode, means for producing a magnetic field about said cathode, said anode having a plurality of electron-receiving portions adjacent said cathode, and a plurality of grooved portions spaced from said electron-receiving portions forming a plurality o-f inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate at a first frequency, relatively low impedance means directly interconnecting alternate electron-receiving portions, each pair o-f electron-receiving portions thus interconnected forming a tuned circuit adapted to oscillate at a second frequency, said second frequency being substantially equal to said first frequency.

6. An electron discharge device kcomprising a cathode and an anode, saidv anode having a plurality of electron-receiving portions adjacent said cathode and circularly disposed around said cathode, and a. plurality of grooved portions spaced from said electron-receiving portions forming a plurality of inductances which together with the interelectrode capacitances constitute a plurality of tuned circuits adapted to oscillate in a first oscillating mode, a lead-in conductor for said cathode lying in a plane extending substantially between two adjacent electron-receiving portions, yalternate electron-receiving portions` being directly interconnected by relatively low impedance means, said loW impedance means directly connecting each of said electron-receiving portions to the two alternate electron-receiving portions With the exception of the two pairs of electron-receiving portions lying on opposite sides of said plane, each of said latter electronreceiving portions being directly connected by said low impedance means only to the alternate electron-receiving portion lying on the same side of said plane, whereby none of said 10W impedance means cross said plane.

7. An electron discharge device comprising a sealed envelope containing an elongated cathi ode, an anode structure having adjacent anode elements defining a transverse cavity resonator, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning element Within said envelope, said tuning element comprising a conductive member supported adjacent said free ends of said anode arms, and means connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.

8. A magnetron comprising a cathode surrounded by an anode block, said block having a central cathode space and interconnecting spaces forming coupled cavity resonators, said block also having a pair of anode arms forming opposite sides of each of said cavity resonators, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning element within said envelope, said tuning element comprising a conductive member supported adjacent said free ends of said anode arms, and means connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.

9. An electron discharge device comprising a sealed envelope containing an elongated cathode, an anode structure having adjacent anode elements defining a transverse cavity resonator, the free ends of said anode arms constituting electron-receiving portions, an adjustable tuning e1- ement within said envelope, said tuning element comprising a conductive member supported adjacent said free ends of said anode arms, and means operable externally of said envelope and connected to said tuning element for adjusting the position of said element toward and away from said cavity resonator.

10. A magnetron comprising a cathode sursaid cavity resonator.

PERCY L. SPENCER!