US 2679615 A
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May 25, 1954 ow 2,679,615
- ELECTRON DISCHARGE DEVICE iled Dec. 51, 1946 4 Sheets-Sheet 1 INVENTOR- Robert/11.3010:
' His Attorney May 25, 1954 R. M. BOWIE ELECTRON DISCHARGE DEVICE 4 Sheets-Sheet 2 Filed Dec. 51, 1946 INVENTOR. Robert M Bpwie V-Q [11's Hl't'orney R. M. BOWIE ELECTRON DISCHARGE DEVICE May 25, 1954 4 Sheets-Sheet 3 Filed Dec. 31, 1946 INVENTOR. Robert M Bowie YKK+ IfisAfloI-ney POSITIVE 2 2 P0 r/v T/AL IVE 6/] TIVE P07 E N 77141.
May 25, 1954 R. M. BOWIE 2,679,615
ELECTRON DISCHARGE DEVICE Filed Dec. 51, 1946 4 Sheets-Sheet 4 IN V EN TOR. Robert/M6011? Patented May 25, 1954 ELECTRON DISCHARGE DEVICE f RohertiM-u BowieaManhasset; ..Ni. Yr, asslginmt to. S lvania Electric .Rroductxlncm a.commotion of Massachusetts:
Application December 31, 1946, Serial No. 719,414
17 Claims 1 This invention relates to ultra-high frequency oscillators of the magnetron type.- More-particularly, i-trel'atesto magnetron oscillators h'aving a plurality of anodes.
Since multi-anodemiag netronsincluding those of the interdigitated -typeare generallychairactei izedby a-l'arge numberof modes ofoscillation, unwanted modes often-tend to manifest them selves; particularly if the magnetron tube is tuned over a broad frequency range; Since: the appearance of unwanted modesof oscillation tends to interfere with the efiiciency ofthe-tube, elaborate precautions have-often beentaken: to widely separate the possible modes of oscillation so that only thewanted oneh-avinga high emc-iency is excited.
Furthermore; in the case-oi the-.interd'igital type of magnetron having acavity resonator, considerable difficulty" has been" experienced in locating thecoupling loop at such aaplaowaswto extract optimum power; Those operatihg tubes of thistype have often encountered'aa; shift of the point at which the optimum power can be removed after the coupling loop has'been located in the cavity-resonatorz For this; reason, it has previously been suggested to introduce certain asymmetries intothe tube structure usually in or near the electron filled spacebetween.v the cathode and anode to distort somewhat the regularpatternof the --cathode anode: space and thereby keep the axis-of symmetry from shifting.
It: is an objectof this invention to design the structure of a magnetron in such-mannerasto provide an improved means or"- fixing the modeof oscillation of suchtubes, particularly thosehaving anodes with peripherally extendingteeth or fingers;
It isafurther object orthisinvention to design amagnetronof this type in such manner as to provide" a means for fixing theazimuthal position of the oscillation so asto .facilitate coupling out. or the radio frequency energy produced therein.
I have found that these'and other advantages which are incidental to its application can' be obtainedby providing means on the anode structure for a phase reversal of the-fingers -at atleast two oppositely placed points onthe annular anode structure.
Referring to the drawings, Fig. 1=is an enlarged longitudinalsectional view through an electron discharge deviceembodying features of 'the'inven ti'onand taken as on line l-l =o'f-F-ig. 2'.
Fig; 2 is a broken transverse sectional View tat:enalon'gthe line-2 2 of-Fig. 1;
Fig; 3'-'=is--an elevation of a-n interdigitatedianode ofthistinventiomshowing aphase'reversal of the finger-shy the provision-of a=so-called -solid=bucke toothon oneof the'anodese Fig; 4-isan elevation of' another former-the interdigitatedanode =of this invention: showing-a phase reversal of -the fingers by the provision of so-cal-led split-bucu-tooth ortwoadiiacentteeth attached to thesame'anodering.
Fig. 5 is an elevatibrr-partl5 411*5901'110111 of the electron discharge device of theinvention -coupl'edwith-a cavityresonator-a nd magnetic meansr Fig;- 6 isa face-view seen: from the under side of'Fig; 5.
Fig; 7 a diagrammatic view showin othe relative position of the interdigitated teeth; the cathodeand' the spacech-a'rge- Figs: 8A; B and c 9A B andrc andf10A-; B and G; arediagraanmatio views illustrative ot th'e power oscillationsofithe electron dischargedevice underspecifiedconditions;
Figs. 11A and .B'are dia-grammatia-views-show+ ing the relative-positions:andzcliargestpresent on the -teeth ot'irrterdigitated anodes constructed in accordaneewiththis inventiom Eig 1 2 lea:diagram'ma'tic-.v-iew otiinterdigitated teeth :of I a; mognetromconstructew in"; accordance withnthisiinvention land-provided :with: a plurality Qf-VOItEILgB nodes Referring to the drawing and more-particularly to -Fig.- 1, I: have illustrated: a preferred a embodiment. of an eleetron. d-ischargeidevice: of this invention; inclu-di'ng anenvelope made' of a suit' able material suoh -a's glass comprising three sect'iona- The-first section indicated bythe numeral l fl is thelower-orheadewsection, the central-356ction-being-indicated by -thenumera'l 1'2} and the topsection or --do'm'e" section being indicated by the-numera'l- Ml The-threesections are separated Icy-and seailed to discs t6 and l 8avvhich maylbe formed of any suitable-conductivemateriaksuch as-oXy -en-freecoppen Within theenvelo'pethere is -prov-ided a thermioni'e cathode -2'8 a'nd a--heat=- ing element 22 which is supported within the cathode between ceramic members M ami 26. anodestructure which includes at first anode member-31E and asecond anode-member -32" surroundsat least a-portion ot-the cathode structure 20 Eacliof the anodemembersincludesaringlike portiomor circular connection: with a plurality'of teeth orfingerlike conductors Is and-3'1 projecting-therefrom substantial/Elvinthe surface of" a cylindrical shell.- The ringmemhenfl; is attachedm any suitahle manne rsuoh-as'byhard soldering'to a fiange portion--15, *wh-ichi's-i-ntegral 3 with the disc 16 and which extends internally of the envelope l4. This provides a convenient arrangement for supporting the anode members as well as to connect them to the disc member I6. Fingers 11 may be provided for supporting the ring against the flange until it is soldered.
The anode member 32 is similarly supported and connected to the lower disc member la. The anode members 30 and 32 are so formed and their extending fingers have such length and width with respect to the space between the adjacent fingers that when they are positioned in the manner illustrated in Figs. 1 and 2, they will be interdigitated or intermeshed with substantially equal spacing between adjacent fingers with the exception of at least two oppositely placed points on the annulus.
At these points on the annulus of each of the anodes, in accordance with my invention, there will be a phase reversal of the fingers. This is accomplished in the embodiments illustrated in the drawings by filling the space normally occupied by a tooth of one anode and the adjoining tooth of the other interdigitated anode by either a large solid buck-tooth 31A, Fig. 3, or two individual teeth 313, Fig. 4, constituting a split bucktooth attached to the same annulus, the following teeth, 36 and 31, being spaced at the regular intervals. This, as can readily be seen in Fig. 3 and Fig. 4, causes a phase reversal of the fingers or teeth. That is, from that point, on up to the next appearance of the buck-tooth, the fingers or teeth 36 project from points on the annulus of the anode which would normally be reserved as a space for the intermeshing teeth 31 of the other anode and its teeth 31 will have been shifted over a like distance on the annulus to make room for teeth 36 thereby resulting in a phase reversal of the teeth. The solid and the split buck-teeth occupy the space required for phase-reversal and are thus properly termed phase-reversal teeth or fingers.
When the anodes are intermeshed, the fingers lie in the surface of a right circular cylinder with its axis substantially coaxial with respect to the cathode. Any suitable number of teeth may be employed for the anode and in the illustrative embodiment of this invention each of the anode members has five or six teeth or fingers depending upon the type.
Any suitable arrangement may be provided for connecting the heater filament 22 to a heater circuit and in the arrangement illustrated in the drawing, lead-in wires 23 and 25 have been provided which may be made of any suitable alloy such as chromium-nickel-iron alloy used for sealing the glass. Lead-in wires may be positioned in any desirable relation and, as shown lead-in wire 23 constitutes a connection and a support through tabs 21 and 29 for the cathode 20 and through a tab 2| for one end of the heater 22 while lead-in wire 25 and tab 3| constitute the connection and support for the other end of the heater.
The anode fingers may be interdigitated to any suitable amount and in the arrangement illustrated in Fig. 1 they are interdigitated over a part of their length, the extremities being indicated by the planes 38 and 39. The planes serve also to indicate the approximate length of the band of electron emissive coating 4| ordinarily used on the cathode but in some cases the band is somewhat longer while for a low power or for continuous non-pulse operation it is frequently advantageous to make the coating band much shorter than that indicated by the planes 38 and 39.
Fingers 42 and 44 on the cathode serve for the purpose of conserving energy by confining the electron discharge within the interdigitated region on the anode.
In order to provide a tunable resonant circuit which is connected between the anode portions 30 and 32, a cavity resonator is provided which includes a box-like portion 52 and a plate or cover portion 54. The envelope may be supported in the opening in the cavity with a disc against shoulders, a relatively tight connection being provided through a reinforcing ring 56 on one of the discs and screws 58. A frame member 60 is in turn attached to the cavity. Brackets or frames 62 and 64 are provided and they are attached to the cavity through screws 66.
In order to provide an arrangement for the conduction of power from the electron discharge device during its operations, a concentric line including tube 10 is provided within which is contained a line 72 which is looped and connected at its inner end 14 to the cavity.
When my electron discharge device is employed as illustrated in the drawing, a magnetic field is employed. This magnetic field may be produced in any suitable manner such as through a magnet indicated generally by the numeral 80. As will be understood by those skilled in the art, the pole pieces of the magnet produce a magnetic field which is substantially parallel with a longitudinal axis of the anode and cathode. An electric field is provided through a source of direct current power indicated by the numeral 82, the positive side being connected to the cavity resonator through a conductor 84 and the negative side connected to the cathode through a line 86. A source of heater-power for the cathode heater 22 may be obtained from a source of power through the heater supply transformer 81.
In order to provide an arrangement for varying the tuning of the electron discharge device, a plurality of tuning screws is provided. Each of these screws cooperate with a tapped bore or guide 92 in the two parts of the cavity resonator 50. It will be noted in the illustrative embodiment of the invention that seven tuning screws are placed at 45 degree intervals except where the line 12 is fitted into the cavity at which point no tuning screw is positioned. It will be understood, however, that both the forms and the number of the tuning screws may be varied to suit such factors as design details of the tube in relation to the cavity resonator dimension. For example, five or nine screws may be placed on the inner and outer block which may contact the upper and lower ends of the cavity resonator either conductively or insulatingly or other forms of suitable resonators may be used in place thereof.
In operation, a magnetic field of the order of 1000 gauss is applied as shown in Fig. 5 and a potential of the order of 1000 volts is applied to the cavity resonator 50 with reference to cathode 20 so that the cavity resonator 50 is positive. This potential may be turned off and on by a modulator so as to achieve pulse modulation, or may be varied through a limited range to achieve frequency modulation. The positive potential of the anode assembly, comprising sets of fingers 36 and 31 relative to the cathode 20, causes electrons to be accelerated radially out- Ward from the cathode; However; the longi tudinal magnetic field causes the eelc-trons: to travel about the-cathode in amanner which" is not" fully understood becauseofthe eiTec-t of space'chargeand the high frequency field' between fingers 36' and 31'. It isbelieved, however, that' these-electrons form a cloud of space charge which maybe visualized asaspok'ed wheel rotating ahou'tthe-cathode with an angular velocity determined bythe following equation:
where w is'tlie'angular-velocity in radians per second, eiSIheOSCiHatiOn frequency. incycles per second andw is: the number of anode segments; Inthe case of a magnetronwith interdigi-tated teeth as in-Fig. 7," n is equal to 12. In the conventional multi'oavity type magnetron, there isbelieved to be as many spokes in this charge wheel as half the-number of segments. This excites the principal or 1|- mode of oscillation. Itis possible to have such a charge wheel inan interdigitated magnetron of the'type shown iii-Fig. '7. However, this leads to the 11- mode of oscillation.
At any instance'all thefingers 36 may be nega tive and all the fingers 3-T'may be positive. Thus the "potentialof all thefingers fit with reference to the potentialof all the fingers 31 varies simultaneously. This mode ofoscillation is of such a form'as' to couple power from the anodes to the cathode. Unlessthe magnetron is specifically designedto extract the power by way of the cathode, this tendsto be a serious channel by which poweris wasted'. It has been pointed out incopending application Serial No. 619,289 filed september 29, 1945, by Donald L. Benedict, that a desirable form of oscillationcan be established'in whichrthe potential-between adjacent fingers is a function of the azimuth angle about the-centerof' the cathode. Fig. Thas been prepared for the purpose of explaining how such a variation may arise.
If instead of there being n/2 spokes of charge in the-cloud I00; there are either (n/2)+1 or (n/Z) -1'spokes; then the desired mode of oscillation maybe exciteds. Fig. 7 has been prepared with (n/2 1' such charge spokes in the cloud I98. This cloud rotates about the cathode with the angular velocity of'ZT/N, where N-is the number of spokes and is equal to (71/2) 1 in the example'shown. When-one such spoke is pointing directly at the upper finger 36, that finger tends to becharged extremely positively by the proximity-of the adjacent negatively charged spoke. The other two fingers 36', above the line AA are rather close to the negatively charged spoke andtendto be somewhat positive. Note that on thelower half of the diagram below the line AA fingers 31 tend to be driven positively by action of the adjacent spokes. Thus, by comparison; fingers 36- below the line A-A' are negative; while they are positive above; If'thecharge cloud iilii rotates it is obvious that the finger having the most positive charge will tend to rotate about the center of the cathode with angular velocity equal to that of'the alternating current power generated by the magnetron. While-the cloud mt is rotating one-fifth of a revolution to the right, the point of maximum positive-charge will make one complete revoluti'on to the left.
This-theory describes a rotating mode-of oscillation which would have no preferred direction in which=powershouldbe extracted: It is ob vious; oi course, that if conditionsare-mightier a wave-to travel around to the left, theyare equally righ-t-ior-one to-travelto the-right, ex-- cept that theme going to the rightwould not be excited by'the electroncloud. In talking of the two waves; the onetraveling.tothe-leitand the one-traveling to'the-right, we-are-nowdealing with-the eleotro-ma-gnetic, oscillationoccurring in the cavity and betweenthe fingers; rather than' w-ith the el'ectron space'charge; excepting asthe=latter generates the wave traveling to the left.
the wave traveling-to the left encounters some-unusual change in impedance in its=path, part: of. it will be-refiected in-the opposite direc+ tion; thus excitingthe wave traveling to the right. It is thischangein impedance which may be provided by the asymmetries described in the Benedict application mentioned above,-
In order to clarify-the above explanation,- ref.- erenoeis made to Fig. 8 particularly-Fig.- 8A. Let the radius-vector R represent instantaneous potential relative to the cathode; When the tube is-non-oscillating, thepotential of all parts of the anode-with respect to-the cathode is-repre sented by the circ1e0. When oscillating; the dotted circle Zp-isthe instantaneous potential appearing onfi'ngers 3-K as a function of position. Note that in the upper half of the di agi'am, above the line AA, the fingers 3b tend to be more positive than theaverage and more negative below the-line AA Thed'ot-dash curve in represents the instantaneous-potential of fingers 3.1. A short instant later in-time this=whole configuration will have rotated to the left; as shown in Fig. 8B?- Still later in time itwillhave reached the position- 86 and so -on. This represents the wave traveling to the left. The wave traveling to the right; mentioned-above; is shown in Figs. 9A; B and 0.
Just as two waves traveling in opposite directions along a transmission line add up to produce standing waves, so these twowaves r0.- tating in* opposite directions add to give standing waves asshownin Figs; 10A, Band C. When the two waves: are substantially in phase. as shown in Figs. 8A and- 9A, thereresults a. high amplitude, as-shown in-Fig. 10A. When the two waves, Fig. 8B and Fig. 9B are approaching out oi-phase condition, the added resultis-as shown in Fig; 103. In Fig. 106 the-resulting wave has changed direction. Thus we seethat if thetwo rotating waves are of equal amplitude, the result' is a-single standing wave oriented ina par.- ticulardirection. It has been shown with the nodes onthe line AM. It: need not. be there: it could equally well be along some other: line.
It is the standing wave condition of Fig; 10 that the means of this invention isintended to achieve. It is achieved, however, not-by reflection, as hasbeennecessaryin'the past, but by so spacing the fingers in the two parts of? the anode asto excite this mode directly;
Reier'now to Fig. 11A. Instead of connecting alternate fingers to the bottom andv top of the cavity respectively, two large fingers 36A and 37A are provided; Each ofithe: large fingers subtends an angle at the center of the cathode. as great as two fingers and the intervening. space of Fig. 7'. In Fig. 7 like fingers are diametrically opposite each other... that is, a: finger 3-! is'always opposite another finger 31; Now returning to Eig. 11A, if! the space charge. I00. breaks. into wheel having: sixspokes,.it. can.be seen: that the oscillation of the type shown in Fig. is excited directly. Upper finger 36' on anode member 36 is at a maximum positive potential at the same instant that lower finger 31' on anode member 31 is also at a maximum positive potential. When the angle between adjacent spokes of charge is exactly equal to the angle between adjacent fingers on the same anode member, a rotating wave is not excited. In the arrangement of Fig. 11A, the potential nodes will fall along the line BB, and the fingers of one anode member to one side of this line will be 130 electrical degrees out of phase with the fingers of the same anode member at the other side of this line. As will be clear from Fig. 10, the amplitude varies from finger to finger, being a maximum for the fingers furthest removed from that line. The instantaneous polarity of the fingers in Fig. 11A is indicated by plus and minus signs, and these signs are doubled opposite fingers of higher potential.
In the alternative arrangement of Fig. 11B the same end is achieved in a slightly different manner. At one side two adjacent fingers 36B are connected to the top of the cavity, while on the other side two adjacent fingers 31B are connected to the bottom of the cavity. Again the potential nodes will lie along the line BB.
In Figs. 11A and 11B, two groups C and C of interdigitated like teeth or fingers are shown, the teeth being substantially alike in contrast to the solid or split buck teeth. The assembled anode members have teeth divided into paired groups, 1. e., an even number of groups (two groups in Fig. 11A and four groups in Fig. 12), with the assembled teeth within a group recurring at a regular pitch and the groups separated by an interval of double pitch suitable ior a buck or phase-reversing tooth. By pitch is meant the distance between the middle of each like finger and of the next adjacent like finger of the anode assembly as, for example, from the center of finger 362 and 312 in Fig. 113. As to one anode member alone, the interdigitated fingers or teeth are likewise divided into an even number of groups by a buck tooth which occupies a greater space than one of the like teeth, and by a space for a buck tooth. The groups of assembled like fingers and the groups of like fingers of one anode member alone are thus seen to be divided or separated by distinctive spacing in contrast to the spacing of the like teeth. The like fingers within a group on one anode member, as teeth 361 and 362 in Fig. 11B, recur at an interval double the pitch of the assembled and interdigitated teeth. The buck teeth, solid or split, occupy a space of double pitch, and the like teeth that flank the buck teeth (as teeth 362 and 363) are mounted at an interval triple the pitch of the assembled teeth, which is one-and-a-half times the mounting interval of the like teeth on one anode member alone.
The practice of providing two large fingers, or solid buck-teeth or the practice of connecting two adjacent fingers to the same side of the cavity as a split buck tooth can be applied to an interdigitated magnetron regardless of the number of anode segments. It is also possible to provide an arrangement of fingers which will set up a mode of oscillation characterized by two sets of voltage nodes in mutually perpendicular directions about the cathode. Such an arrangement is shown in Fig. 12. Here, two large fingers or solid buck teeth 2-a are shown in two positions and in two other positions adjacent fingers l constituting split buck teeth are connected with the same side of the cavity. Voltage nodes are set up along lines BB and B" 3".
Once having fixedly established the position of the voltage nodes by the means of this invention, power may readily be coupled out of the cavity resonator by any suitable device such as, for example, a p which extends into an opening in the periphery of the cavity resonator. The coupling loop is inductively coupled to the magnetic field set up in the cavity resonator by the oscillations.
While the above description and the drawings submitted herewith disclose preferred and practiced embodiments of the electron discharge device of this invention, it will be understood, by those skilled in the art, that the specific means for fixedly establishing the voltage nodes shown and described are by way of illustration and are not to be construed as limiting the invention.
What I claim is:
l. A magnetron anode assembly having a plurality of annular anode members provided with similar interdigitated fingers forming an annular structure, said assembly additionally including paired buck teeth oppositely disposed to each other in said annular structure.
2. An electron discharge device comprising an axially extending cathode, a pair of anode members surrounding said cathode forming an annular structure, each of said anode members including a plurality of axially extending, peripherally spaced fingers, a buck-tooth on each of said anode members, the buck-teeth being oppositely disposed to each other on the interdigitated annular structure for reversing the phase of the fingers on opposite sides of the anode structure.
3. A magnetron device having an axially extending cathode and an annular anode structure including a pair of annular anode members, each anode member surrounding said cathode and each anode member having an annulus, a. plurality of axially extending, peripherally spaced fingers, said fingers being divided into oppositely placed groups on each annulus, the fingers within each group being equally spaced and, said groups on each annulus being separated from each other by a buck-tooth on the one side and a corresponding large space on the other side.
4. An electron discharge device comprising an axially extending cathode, a pair of anode members surrounding said cathode, each of said anode members including a plurality of like axially extending, peripherally spaced fingers, the fingers of each anode member being divided into an even number of groups by spacing between the groups that is difierent from the spacing between the fingers within a group, said anode members being surrounded by and electrically connected to a cavity resonator.
5. An electron discharge device comprising an axially extending cathode, a pair of anode members surrounding said cathode, forming an annular structure, each of said anode members including a plurality of axially extending, peripherally spaced fingers, a buck-tooth on each of said anode members oppositely disposed to each other on the interdigitated annular structure for reversing the phase of the fingers on opposite sides of the anode members, a glass envelope surrounding said cathode and anode members, a pair of spaced discs sealed to said envelope and having portions extending internally and externally of said envelope, said anode members being supported by and electrically connected to said internal portions of said discs.
6. A magnetron having a cathode, a pair of cylindrical anode members coaxially surrounding said cathode, each of said members having a circular connector and a plurality of like conductors extending axially from said connector, the conductors of one of said anode members being interposed between the conductors of the other of said anode members, said conductors being mounted at regular pitch intervals, said anode members additionally embodying diametrically opposite conductors each occupying a space of double pitch.
7. A magnetron having a cathode and a pair of coaxial anode members, each anode member having like conductors interposed between the like conductors of the other of said anode members, all of said like conductors being mounted at regular pitch intervals and divided into an even number of groups by three times one of said regular intervals, and a phasereversing conductor mounted on one of said members between said groups of conductors and occupying a space of double pitch.
8. An anode member for an interdigital magnetron, said anode member comprising a circular connector and a plurality of conductors axially extending therefrom, certain of said conductors being mounted at regular intervals, a certain pair of said conductors being mounted at one-and-ahalf times said regular interval.
9. A magnetron having a cathode, and a coaxial pair of anode members, each anode member including a circular connector and a plurality of conductors extending axially therefrom and mounted at regular intervals within groups of conductors, a pair of said conductors on each circular connector being mounted at one-anda-half times one of said regular intervals between said groups, the conductors of each anode member extending into spaces between the conductors of the other anode member.
10. A magnetron comprising a cathode and a pair of coaxial anode members, each of said anode members including a circular connector and a plurality of conductors extending axially therefrom, said anode members being assembled with the conductors of one of said anode members interposed between the conductors of the other of said anode members, the conductors of each anode member being mounted diametrically opposite conductors of the opposite anode member, the assembled conductors being divided into an even number of groups wherein the conductors within a group are mounted at a regular pitch and the separation of the conductors between the groups is of greater pitch.
11. A magnetron having an axially extending cathode, an annular anode structure surrounding said cathode and including two anode members each including peripherally spaced interconnected axially extending like fingers interdigitated with the fingers of the other of said 10 anode members, said like fingers being divided into groups by separation between the groups that is different from the separation of said like fingers within a group.
12. A magnetron device having an assembly including plural anode elements having projecting fingers, said elements being assembled with said fingers interdigitated and the fingers in said assembly being divided into an even number of groups within which the pitch of the fingers is regular and the groups of fingers being separated by spaces each equal to twice said pitch.
13. A magnetron device in accordance with claim 12 in which said assembly includes buck teeth larger than said fingers, and said spaces are occupied by said buck teeth.
14. A magnetron device having a plurality of anode members provided with similar interdigitated fingers, the fingers of each member being divided into an even number of groups, the spacing between the groups of fingers on one anode member being difierent from the spacing between the fingers on one anode member within a group.
15. A magnetron having an axially extending cathode and an annular anode structure surrounding said cathode, a plurality of axially extending peripherally spaced similar fingers,
said similar fingers forming part of said anode structure and being divided into paired groups on the annular structure, the similar fingers of each group being mounted at peripheral points of equal spacing and the similar fingers at the ends of adjacent groups being separated from each other by spacing difierent from said equal spacing.
16. A magnetron device comprising plural anode members having groups of like interdigitated fingers, the fingers of the groups on each of the anode members being mounted at peripheral points of equal spacing and said groups being separated from each other by spacing different from said equal spacing.
17. A magnetron device including lural anode members having groups of like interdigitated fingers, the like fingers of the groups on each of the anode members being mounted at peripheral points of equal spacing and said groups being separated from each other by spacing different from said equal spacing, adjacent groups on each anode member being out of phase during operation.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,128,237 Dallenbach Aug. 30, 1938 2,147,159 Gutton et a1 Feb. 14, 1939 2,168,295 De Vries et al -Aug. 1, 1939 2,424,886 Hansell July 29, 1947 OTHER REFERENCES Proceedings I. R. E. and Waves and Electrons, vol. 35, pp. 361-369, No. 4, April 1947. (Original manuscript received by the Institute Mar. 29, 1946.)