US2599237A - Magnetron generator - Google Patents

Description

June 3, 1952 c. cucclA MAGNETRON GENERATOR 5 Sheets-Sheet l Filed July 5l, 1947 June 3, 1952 Q CUCClA 2,599,237

MAGNETRON GENERATOR Filed July 51, 1947 3 Sheets-Sheet 2 Snnentor Ziff/aen L. @yaca Gttomeg June 3, 1952 c. l.. cUccxA MAGNETRON GENERATOR 5 Sheets-Sheet 5 Filed July 5l, 1947 INVENTOR. Carmel: L. "zz .2 2M

TTORNEY axially to the cathode-anode chamber.

Patented June 3, 1952 MAGNETRON GENERATOR Carmen L. Cuccia, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 31, 1947, Serial No. 765,028

18 Claims.

posed thermionic cathode surrounded by a plurality of radially extending anode vanes or segments which form a plurality of radially extending anode cavity resonators tuned to the operating microwave frequency. A source of constant operating potential is connected between the cathode and anode in a manner whereby the anode is at a positive direct-current potential with respect to the cathode. A substantially constant intensity magnetic field is applied Electrical charges accumulate on the anode vane tips adjacent to the cathode, resulting in oscillatory electric fields, hereinafter termed electric fields, in the anode cavity resonators which fields interact withv the electrons travelling in cycloidal paths from the cathode to the anode, thus abstracting energy from the travelling electrons and producing sustained oscillations at the operating microwave frequency. An inverted variation of the conventional magnetron structure comprises a centrally disposed gear-shaped anode having a plurality of radiallylextending peripheral anode cavities, the anode structure being surrounded by a cylindrical electron-emissive cathode, and the entire structure being subjected to an axial constant intensity magnetic field.

In accordance with the instant invention, the geometries of the conventional and inverted magnetron generators described heretofore are combined in a manner whereby a centrally disposed cathode and surrounding radially disposed anode vanes comprise a magnetron generator, and a peripherally disposed ring-shaped second cathode surrounds an axially-extended portion of the anode, the entire structure being subjected'to a constant intensity magnetic field extending trans- The anode is positively biased both, of the generated oscillations may be modulated. A shield or other device disposed between the second cathode and the remaining portion of the anode structure, and biased negatively with 51;;respect to the anode structure, causes the electron emission from the second cathode to be directed substantially only to the extended portion of the anode structure, and to be effectively shielded from the remainder of the anode struceture.

If desired, the simple second cathode and cathode shield structure may be replaced by a more elaborate ring-shaped modulating electron gun structure including a control grid and, if desired,

; additional electron beam-forming grids, whereby electrons emitted from the inside surface of the modulating electron gun ring are directed substantially only to the extended anode cavity vane tips.

20, When a novel magnetron of the type described is operated with suitable magnetic eld and dlrect-current operating potentials applied between the anode and the two cathodes, microwave oscillations will result, and electric fields of thede- 25. sired mode of operation will be established in the cavity resonators between the anode vanes.

When an electric field is established inside the resonator, an electric field of the same angular velocity will exist between the adjacent extended 301 anode vane tips on the outside thereof, in the space between the Vane tips and the modulating outer cathode. If, during oscillation, a directcurrent potential is impressed between thelmodulating cathode and the anode vanes, then, due

to action of the magnetic field, the electronsemitted by the modulating cathode will travel toward the vane tips in cycloidal paths and interact with the outside vane tip electric field and induce currents in the vane structures. The 40 axial magnetic field, the geometry of the tube structure, and the direct-current operating potentials applied thereto, can be so adjusted that these induced currents are out-of-phase with the normal circulating currents in the vanes, and a frequency shift, or a change in oscillation amplitude, or both, can be obtained. All of the axially.

disposed anode cavity resonators are subjected to the same interaction simultaneously so that electric field symmetry is preserved.

posed resonators simulate a cylindrical shell.'

A modification of the devices described hereto- The presence o1 the central cathode and the axial magnetic iield will cause this system to generate microwave oscillations of the frequency determined by the proportions of the parallel resonators. A travelling electric iield will exist on the outside tips of the anode vanes, said eld having the same angular velocity as the internal electric field. Electrons drawn to the resonator vanes from the outer modulating cathode will interact with the outer electric iield, thus providing frequency or amplitude modulation of the generated oscillations.

Among the objects of the invention are torprovide improved means for modulating magnetron microwave generators. Another 'object is to provide improved means for providing frequency modulation, amplitude modulation, or both types of modulation, of microwave oscillations` generated under conditions of magnetron operation. A further object of the invention is to provide an improved microwave magnetron structure comprising a central cathode, an intermediate anode structure having a plurality of radially disposedanode vanes, and an external cylindrical modulating electron beam generating structure operative upon the adjacent anode vane tips. Another ob-'ject of the invention is to provide an improved microwave generator including means for modulating either the frequency or the amplitude of the generating microwave oscillations wherein the :intensity of an axial magnetic ield is adjusted to provide eiiicient magnetron generator operation, and the desired type of vsignal modulation of the generated. oscillations.

The invention will be described.l in greater detailbyy reference to the accompanying drawings' of which Figure l is a schematic diagram of a conventional magnetron generator; Figure 2 is a schematic diagram of an inverted magnetron microwavegenerator; Figure 3 is a cross-sectional, elevational, partially-schematic view of a first embodiment of the instant invention taken along the-section line III- III of Fig. 4; Figure 4 is a plan, cross-sectional, partially-schematic view, taken-along the section line IV-IV of Figure 3, ofesaid first embodiment of the invention; Figure 5'is a. fragmentary plan view, taken along the section lineIV-IV of Figure 3,` of a modification of said first embodiment of the invention; Figure is a perspective fragmentary view of a second embodiment of the invention; Figure 7 is a cross-sectional, elevational, partly sectional view of. a preferred modic'ation of said first embodimentof the invention; Figure 8 is aside elevational cross-sectional view taken alongv the section line VIII- VIII of Figure 7; and Figure 9 isa plan cross-sectional view taken along the section line IX-IX of Figure '7. Similar reference characters are applied to similar elements throughout the drawings.

Referring to the drawings, Figure l illustrates schematically a conventional magnetron structure comprising a central elongated electronemissivecathode I surrounded by a'pluralityof radial anode. vanes 3 and enclosed within an evacuated conductive envelope 5 to which the radial anode vanes` are connected. A source of direct-current operating potential is connected between anode and cathode ina manner whereby the .anode is positively biased with respect to the-cathode. An axial, constant intensity, magnetic eld indicated by the designation 'I is applied'to the device from an external magnet structure not shown. The operation of such conventional magnetrons is well known in the art and will not be described in detail herein. Microwave energy for a load, not shown, is derived from a coupling loop 9 coupled into one of the anode cavity resonators II formed by the radial anode vanes 3 and the conductive outer wall 5. The anode cavity resonators are tuned to resonate in radial modes at the desired operating frequency. The coupling loop 9 is coupled through a coaxial line I3 to the load.

Figure 2 illustrates an inverted modification ofthe standard magnetron generator of Figure 1 wherein the elements are inter-changed, the anode comprising a central cylindrical element Iii-having a plurality -of radially extending vanes 3', the anode structure being surrounded by an evacuated metallic cylindrical envelope 5. The inner surface of the cylindrical envelope 5' supports string-shaped cathode I which may be either directly or indirectly heated. The output coupling loop S is coupled through a suitable aperture I'Iv in the anode structure I5Lto lan external load not shown. The spaces betweenadjacent anode vanes 3 comprise the anode vresenators which are tuned to resonate in radialmodes at the operating microwave frequency. In either of the devices of Figures 1 ariel 2, alternate anode vane tips may be connected together by one or more pairs of concentric .anode vane connector rings in Aaccordance with ,knowntechnique, and as shown kinligures 3:, 4 and 5.

Referring to Figures 3 ande, a combination of the structuresof Figures 1 and 2'is employed, according to the "invention, to provide a micro.- Wave magnetron generator having a modulating electron-emissive structure disposed externally of a portion of the anode vane tips. The central cathode I, supported by suitable. .means not.,

shown, is surrounded by a ,plurality ofradiallyextending anode vanes 3v enclosed within an evacuated metallic envelope 5 .as in the device of Figure 1; The anode vanes define therebetween a plurality of anode cavity resonators 4tuned to resonate in radial modesv at theoperating frequency. Theinner ends; or'vane tips. I9. of the,

anode vanes. 3are extended axially, upwardly in Fig. 3, and alternate vanes are connected together by. a pairof concentric rings .2I.

anode vanes. '3 at thelower ends.V thereof. The

projecting vane tips- I9 and ringsy i2I are sur-- rounded by `a .ring-shaped second cathode 25 shielded from the remainder of the anodevane. structures by a Lring-shaped shield .'21 which is.

maintainedL at the same potential as the second cathode 25, or, maybe negatively biased with respect thereto. The anode vanes 3 are positively biasedwith respect to thecentral cathode I and with respect to the outer or modulating cathode 25, so that the rings 2'I serve. as collector rings. A source of modulating signals is connected between the outer cathode 25 andl the anode vanestructure to vary the reactive orv conductive eiect of the modulating electron beam emission :in response to the modulating signals. as described'heretofore. The. device is subjected to an axialrmagnetic field, as indicated at'1, 'the intensity of whichl mayv be adjustedA to.A provide maximum magnetron generator` eiiiciency and also the desired type :and degree of modulation ofthe generated oscillations as will be described in greater detail hereinafter. The dii-ferent magnetic iield intensi-ties applied to differentfpor- Y tions of the device may be provided-'by tapering Similar rings 23 connect together alternate ones of they nique. Modulated microwaves may be derived from the device by means of the coupling loop 9 and coaxial transmission line I3 coupling the device to a load, not shown.

Figure 5 discloses a modiiication of the devicev described by reference to Figures 3 and 4 wherein the modulating electron beam structure includes a control grid 29 and one or more beam forming grids 3l having a plurality of apertures 33 aligned with the several extended anode vane tips I3. By biasing the beam forming grid 3| positively with respect to the cathode 25, the electron emission therefrom is more eiciently directed to the extended anode vane tips .I9 than in Figs. 3 and 4. The modulating signal source is con.. nected between the control grid 29 and the cathode 25 to modulate the electron emission to the extended anode vane tips I3. The concentric cathode, control grid and beam forming grids may v be :supported in any desired manner adjacent to the.upwardly projecting anode vane tips I9 andmay be of any suitable design to provide the desired focussing of the modulating electron emission to concentrate said emission on the adjacent anode vane tips.

The device illustrated in Figure 6 is similar to that described heretofore by reference to Figures 3 and 4 with the exception that the central cathode I does not extend the full axial length of the anode vanes 3, and the vanes 3" are extended axially of the device to provide effectively axiallyelongated parallel disposed resonators resonating in longitudinal or axial modes. The modulating electron beam structure including the cathode 25 surrounds the upper portion of the anode vanes 3 concentric with the central cathode I. The ends of the anode vanes 3 may be alternately connected together by vane connecting rings as described heretofore.

Referring to Figures 7, 8 and 9, a preferred embodiment of the invention utilizes a modified RCA type 2J41 microwave magnetron comprising an evacuated metallic envelope 5 in which is enclosed a pair of magnetic iron pole pieces 4I, 43, between which are positioned an axially disposed indirectly heated cathode I and a coaxial assembly of radially disposed anode vanes 3 supported by a heavy transverse metallic block 45 mounted on the base 53 of the envelope 5. An

axially adjustable apertured flat tuning member 4l is disposed adjacent to one end of the anode cavity resonator assembly. The tuning member `Ill is fastened to the block 45 at the point 49 and is axially adjustable over a limited range by movement of the pin 5I secured to the opposite end thereof. The pin 5I is flexibly secured to the base 53 of the tube envelope, and its location is determined by a set-screw 55 in a block 5l on the base 53. Thev radially disposed anode vanes and the block 45 are cut away as indicated at 59 to provide a plurality ofanode vane tips I9 around which is disposed a ring-shaped modulating electron beam cathode 25. The modulating -cathode25 is surrcundedV on theV three sides re- .movedfrom the ,vane tips I9 by a hollow ringshaped shield 28 which shields the modulating beam cathode from the remainder of the anode structure and from the magnetic pole pieces 4I and 43.

The pole pieces 4I', 43 are supported on the transverse block 45 by heavy cylindrical insulat- "orsSI, 63 and transverse brackets65, v6'I.

Separate terminals are brought out through the evacuated envelope for the central cathode and heater connections, as well as for the modulating 6 beam cathode 25 and, if desired, forth cathode shield 28. If desired, the modulating cathode 25 and shield 28 may be connected together inside of the tube envelope. alternately strapped together, at the end remote from the modulating beam cathode25, by a pair of concentric rings 23. Modulated microwave energy is applied toa load, not shown, by means of Va coaxial transmission line I3 extending throughV the envelope and terminated in a coupling loop 9 disposed within one of the anode cavity resonators. The external magnet structure, not shown, for supplying the constant intensity axial magnetic field is closely fitted to the device adjacent to the outer ends of the magnetic pole pieces 4I, 43 whereby an axial magnetic field indicated by the arrows 'I is provided.

The operation of the device described in Figures 6, 7 and 8 is in al1 essential respects similar to that described heretofore with respect to the device illustrated in Figures 3 and 4. v

It has long been known that as a magnetron of the multicavity type with a central cathode is turned on, the presence of space charges in the space between the cathode and vane tips produces an electronic admittance in shunt with the cavities which will change the frequencyof the magnetron as it operates. This is known as pushing and the amount of pushingwillin general increase as the current is increased for most ranges of application. See Stabilized Magnetron for Beacon Service by Donal, Cuccia and Brown, RCA Review, June 1947.

Pushing is due to the fact that as the electrons circle around the central cathode with increasing radius as they'proceed to the vane tips due to the radial direct current field they will interact with the inner electric fields between the anode varies E1 in Figure 4. Energy will be exchanged, some electrons giving up energy to the field El, some removing energy from the eld E1. This exchange will go on all the time and, in a high eiiiciency magnetron, the electrons will bunch as they approach the vane tips and will eventually give up their energy. As this energy exchanging progresses, the interactions will appear to have susceptance as seen by the cavities to an extent dependent upon the net energy given up and then extracted from the field E1 during a complete cycle of oscillation.

Pushing in general is undesirable" but tolerable and is inherent in normal magnetrons. In thisinvention, a structure base on an inverted magnetron is incorporated into a normal structure and will provide a pushing mechanism which is independent of the central interaction space. Essentially speaking, the electrons emitted from the modulating cathode will, due to a `direct current field between the modulating cathode and the vane tips, travel toward the vane tips 'and interact with the outer electric field, E2 in Fig. 4, which are produced by the oscillations due to electrons from the central cathode in normal magnetron fashion, and either frequency modulation or amplitude modulation can be obtained. This is because as the electrons leave the modulating cathode in purely random fashion they will react with the outer elds Ez. If they are in the presence of a magnetic iield of suitable intensity and a suitable direct current iield, they will bunch after repeated interactions and absorb energy from the eld Ez, and amplitude modulation will take place. If, using suitable magnetic field and direct current field, they interact with E2 so that no net energy exchange takes place during afcycle The anode vanes 3 are` ...9 i If the manipulations are carriedv through, using a perturbation methodV of solution,

see Smith and Shulman Frequency Modulation and Control by Electron Beams. Proceedings of I. R. E., July 1947,

where is the change in frequency due to injected electrons, Qon is the Q of the cavity with the injected electrons, and the magnetron is operating in the n =Z2`r mode Aon* is the conjugate of the vector potential, and R. P. and I. P. means the real part and imaginary parts, respectively.

Equation 13 represents a small quantity due to the fact that it is calculated from the unperturbed field but is valid and suitable for this discussion. Substituting Equations 1 and 2 for the central cathode regions into Equations 11 and 12, the frequency change in this central cathode region may be approximated as TL m (9].)1 Evin-6h12 which shows that the pushing is a function of Ia, which is the current, and of the static eld conditions.

It is convenient, however, to perform this pushing or loading in the inverted magnetron structure region where the static eld conditions may be approximated and where the oscillating field is produced by the central cathode structure.

Comparing Equations 3 and 4 with Equations 1 and 2, it is seen that the oscillating field falls oli less rapidly in passing from the outer vane tips to the outer cathode than-in passingfrom the inner vane tips to the central cathode. Since the current may be made large due to the large surface of the outer cathode and due to the fact that bunching may take place in the region between the outer vane tips and the outer cathode, see Equation 8, an expression similar to Equation l5 which may be derived for this region will show that high pushing or high loading may be achieved depending on the value of a. This angle will be controlled by suitable choices of En, which' is determined by the power 'into the central cathode region, the magnetic leld intensity H, and the direct current radial field between the outer vane tips and the outer cathode. Once the control-parameters `are suitably chosen, the

.16 use of the grid in the outer cathode structure will permit further control of the frequency change of the energy absorption. Y

Some care must be taken that the modulating structure does not break into oscillation with applied modulating signals due to the interactions in the inverted magnetron structure'region. However, this condition is 'rather unlikely since the inverted magnetron is not a goodv oscillator due to the fact that the modes of oscillation may overlap and inefficient energy exchange will take place.

Thus the invention described comprises an improved method of and means for modulating either the frequency or the amplitude, or both, of a microwave magnetron generator wherein a second electron-emissive cathode isdisposed around the periphery of a portion of the magnetron anode cavity vane tips. Electron emission from the outer cathode interacts with the microwavev electric fields established within the magnetron cavity resonators, thus inducing outof-phase currents in the anode cavity vanes which react upon the vgenerated oscillations. V".lhe type and degree of modulation is dependent upon the operating voltages applied tothe various elementsof the device and to the intensity of the applied axial magnetic field relative'to the frequency of the generated oscillations. Modulating signals are applied to the auxiliary electron beam generating means to` control the amount of electron emission therefrom which lmpinges upon the anode vane tips. A grid-controlled beam-type modulating structure is disclosed for providing improved control by the applied modulating signals. A practical structure comprising a modilcation of anA existing type magnetron tube is disclosed.

I claim as my invention:

l. A magnetron microwave generator includ ing a 'rst electron-emissive cathode, an anode disposed adjacent said cathode, means adjacent said anode for subjecting electrons from said cathode to a substantially constant intensity transverse magnetic field, means connected -to said cathode and said anode for applying operating potentials thereto to generate microwave oscillations on said anode, a second electronemissive cathode surounding a portion of said anode, shielding means interposed between said second cathode and the remainder of said anode for directing electrons emitted by said second cathode to impinge upon said anode portion, and. means connected to said second cathode and said anode for applying vmodulating potentials thereto for controlling said directed anode for directing electrons emitted by said second cathode to impinge upon said anode portion in a direction substantially transverse to `said magnetic field, and means for controlling said directed electrons to modulate said oscillations. 3. A magnetron microwave generating sysconnecte -teni; includingan electronsemissirar-cathode,-L an anodey disposed* adjacent saldi cathodef means nfor subjecting electrons from-saidI cathodeito asub'- stantia'llyf constant intensityf transverse=magnetic iiel'd,means-for' applyingoperatingpotentials to saideanodee andlcathodeto generate=microwave -osoiiiatienss onqv said; anode,- anv electron source portion` off: said'f anodeg means Y of;said'-sourceeforfdirectingvelectrons emittedflbyr said'p source'` to impi-nge uponl said anode, means-for subjectingftheeleetronsifrom said source to a transverse magnetic eldffof sucl'r' intensitjr1 that said;V electrons do not absorbs energy# fromA said" microwave oscillations dui-ineacyclef-ot'said' osr-yillations; wherebyfsaid electrons constitute aV pure5l reactive loadt onfsaid anode;- and modulation signal inputl'meanslcone 'neej-,edf tosaidf electr-onf sourceaforVY controlling saidfdireetedf'electrons Vto modulaterthefrequency of? said? oscillations;

4;; Afmagnetronf microwave generating: system including` anl electronemissive cathode; anl anode disposed adjacent said cathode, meansfforsubfjecting' el'ectronsf` fromV said: cathode to a substantially constantvintensity transverse` magnetic: eld,l means foru applyingY operatingV po- 'terrtials-L tof said anode -and i cathode 1 to generate microwave oscillations on said' anode, anV electroni sour-cef surroundinga` portion of"`said anode,

` 'means-f. connected' torsaid'v'lsourceffor directing electrons'emitted by-.said' sourcer to :impinge upon said? anode,`- means fzr-f-subjectingfthe electrons from; ,saidfsource .toA a transverse magnetic field of? suchintensity that' said' electrons absorb energy f from said? microwave escill'ations;t and modulationfsignal inputmeans connectedtol said- 'electron4 source; for controlling: said.' directed electrons to modulatesthefrfamplitudeof'saidf'os Cillations.

51T A magnetron:microwave. generator includinea; rstelectron-emissive cathode, a plurality ctn-adir'allyI disposed cavityfresonator'- anodes disposed-'- around'` and adjacent to said'4 cathode, mean-saadjacentf saidf anoder forA subjectingA electr,onsfrrom saidfcathodelto: a: substantiallyfcon- A starrt lintensity transversemagneticfield; means connected to said cathode` and:A saidH anode: forapplying operating potentials thereto-to gen era-te microwave oscillations inV said'.` resonator amados;- aY second electron-emissive cathode sur'- roundingf a portionv of said anodes; shielding means interposed between said second-- cathode andftlie remainder ofsaid anodes-i for directingr electronsemitted' by said" second cathode to im'- roundingv` af portion of-f4 said vanodes; shielding means interposed between said second cathode andi'tlie remainder-fof said -anodes for; directing electronsemitted by saidsecond'cathode to impinge upon said portion of said anodesV in a direction ytransverse :tof said magnetic field, and Y cathode, av pluralityrof liZ meansfrcrfcontrollinafsaidzdirectedz electrons-#to modulate saidjoscillation3,:`

7. A magnetron microwave generating system including a rstl'eleetroneeniissive cathode, a plurality of radiallydi-spesedcavityresonator anodes disposed aroundiand adcafnl? to said cathode, means for subjecting electrons from said cathode to a substantially constant intensityftransyerse magnetic field, means-for applying operating potentials tovsaidanodes and cathode to generate microwave oscillationsn saidgresonator anodes, a pIuralit-vrof` electron beamgsources surrounding a portion of said anodes, shielding means interposed between said sourjces and the remainder of said anod'esaforgdirecting electrons emitted by each of said:soureesto-:impingeupon. said portionl of said anodesanmeans for controlling said directed electrons tosmodulate said oscillations.

821A, tube.; including' a firs@ eletronxemissive aly tive anodes disposed air-@11nd"SaidA cent ones of said anodes forming a pluralityl of cavity resonators and each of said anodes includ'- ing a projecting portion substantially separate from said resonators, asecond electron-emissive cathode; surrounding said projecting, portions. of saidsanodes and shielding-means.internosedbef tween said., second cathode and. theremainder of said anodes for directinguelectrons emitted by said second cathode tOJmpinge-upon said projecting portions of said anodes.

9. Agmicrowave, tubefinclridingl a vforst electron;- emissi.ve-:cathoda-v arpluralityot radially: disposed conductive anodes disposed around-maid cathode ai PLlLUa-l'lolofi conductiyezeelemmts connectingggtoesther alternate ones;v cfr saidanodes, adjacent Oneszor.sadranodesfforming a, plurality-of: cavity resonators andaeach` .ofsaidianodes including a project-ing;Y portion substantially; separate.- from saidzgrescnators,,arsecond;eleetronfemissivefcathr ode surrounding.saidfprojeetnsgportions (1i-said anodes and shielding means interposed between said seccndicatliodeg andv the remainder of said anodes for directing-electrons, emitted by said second cathode to, impinge upon said projecting portions of saidjanod.

10. A microwave-tubeincluding a iirst electronemissive cathode, a'fplurality of radially disposed conductive; anodesidisppsedaround saidmathode,

anodes,` forf'directine., electronsaemittedby each ofv said sources-t impinsetuponione? of said proictng-'portionscofzsaidianodes.

12'.' A magnet-ron',microwavegenerating` system includingalrstelectronemissive cathodaaplu.-

- rality ofrradiallyidispnssdnonductive anodes disiposed adjacent said cathode, adjacent ones of said anodes forming a plurality oi' cavity resonators and each of said anodes including a projecting portion substantially separate from said resonators, means for subjecting electrons emitted from said cathode to a substantially constant intensity magnetic field, means for applying operat- Y ing potentials to said anodes and cathode to gensaid directed electrons to modulate said oscillations.

13. A magnetron microwave generating system including a first electron-emissive cathode, a plurality of radially disposed conductive anodes disposed adjacent said cathode, adjacent ones of said anodes forming a plurality of substantially paralleldisposed cavity resonators operative in axial modes, means for subjecting electrons emitted from said cathode to an axial substantially -constant intensity magnetic iield, means for applying operating potentials to said anodes and cathode to generate microwave oscillations on said anodes and in said resonators, a second electron-emissive cathode surrounding said anodes and Aoperative upon the traveling microalternately connected together and disposed adjacent said cathode, adjacent ones of said anodes A forming a plurality of radially disposed cavity wave iield on the peripheries of said anodes,

shielding means interposed between said second cathode and the remainder of said anodes for directing electrons emitted by said second cathode to impinge upon said peripheral portions of said anodes in a direction transverse to said magnetic iield to interact with said traveling microwave iields thereon, and means for controlling said directed electrons to modulate said oscillations.

14. A microwave tube including a rst electron-emissive cathode, a plurality of radially disposed conductive anodes disposed around said cathode, adjacent ones of said anodes forming a plurality of radially disposed cavity resonators and each of said anodes including an axially projecting portion substantially separate from saidr resonators, a second electron-emissive cathode surrounding said projecting portions of said anodes, a support for said second cathode interposed between said second cathode and the remainder of said anodes and effectively shielding i resonators and each of said anodes including an axially projecting portion substantially separate from said resonators, means for subjecting electrons emitted from said cathode to a substantially constant intensity magnetic field, means for applying operating potentials to said anodes and cathode to establish microwave elds between said projecting portions of adjacent ones of said anodes and in said resonators, a second electronemissive cathode surrounding said projecting portions of said anodes and shielding means interposed between said second cathode and the remainder of said anodes for directing electrons emitted by said second cathode to impinge upon said projecting portions of said anodes in a direction transverse to said magnetic eld to interact with said fields between said projecting portions of said anodes, and means for controlling simultaneously the energy of said directed electrons to modulate said oscillations.

16. A microwave tube comprising a central cathode, an anode surrounding said cathode and comprising axially extending portions and radlally extending portions, a second cathode insulated from said central cathode and said anode andsurrounding said axially extending portions of said anode and a shield interposed between said second cathode and said radially extending portions of said anode.

17. A tube according to claim 16 including means connected to said anode and cathodes for applying separate operating potentials thereto and means adjacent said anode for applying an axial magnetic eld to said cathodes and anode.

18. A microwave tube comprising an elongated central cathode, an anode comprising a plurality of conductive vanes surrounding said cathode, each lof said vanes comprising a radially extending portion and an `axially extending portion, adjacent ones of said vanes forming cavity resonators tuned to the operating microwave frequency, a second cathode surrounding said ,axially extending portions, a shield interposed between said second cathode and said radially extending portions, means connected to said anode and cathodes for applying separate operating potentials thereto, and means adjacent said anode for applying an axial magnetic field to said cathodes and anode.

CARMEN L. CUCCIA.

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

UNITED STATES PATENTS Number Name Date 1,303,579 Nicolson May 13, 1919 2,067,607 Hitchcock Jan. 12, 1937 2,463,512 Brown Mar. 8, 1949 2,468,183 Derby Apr. 26.1949 2,468,243 Spencer Apr. 26, 1949

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