US2617079A

US2617079A - Tunable magnetron

Info

Publication number: US2617079A
Application number: US548530A
Authority: US
Inventors: John W Mcnall
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1944-08-08
Filing date: 1944-08-08
Publication date: 1952-11-04
Anticipated expiration: 1969-11-04
Also published as: BE473432A; GB635832A; FR947152A

Description

Nov. 4, 19.52 J, W MCNALL 2,617,079

TUNABLE MGNETRON Filed Aug. 8, 19,44 2 SHEETS- SHEET 1 141:9. j. Z0 M Tf 1g 2,; 15 11 [Z1 lq 11 Z1 15 2\ Wk W gy j Y 4 16 Y l M j j M- 5 l z5 5 v 14 f 14 15 6/ -f10 'Z' 'A all.' .7 Z5 .j Z z5 l Z4 Y 3/ 15 j6// l 1f/ A 15 Il l j l Z j] Z1 15 11 13 j 15 zo .Z1 11 INVENTOR .I W. Mf/VHU.

B WWW?- ATTORNEY NOV. 4, 1952 W. MCNALL n TUNABLE MAGNETRON Filed Aug. 8, 1944 2 SHEETS-SHEET 2 ze 1511 1g BY nwwf ATTORNEY Patented Nov. 4, 1952 TUN ABLE MAGrNETRON John W. McNalLEast Orange, N. J., assignor to Westinghouse; Electric Corporation, East yPitts- "burgh,"Pa., ,a corporation of Pennsylvania :Application August 8, 1944, SeriallNo. 548, 53 0 (Cl. I315-40) 31 .(llaims. l

Thisl invention relates' to magnetrons, and more particularly to tuning means for the same.

A recent kdevelopment in this art has --ibeen termed "Crownof ThornsWas-somewhat descriptive of a tuningmeans for a magnetron, and consisting `of-a plurality ofprongs, one ineach of several resonant cavities of a magnetron, `and carried from a complete or `partial ring Aat the ends of the cavities so the several prongs may be moved longitudinally and simultaneously in the cavities. The ring is mechanically-connected by rod or lever through a flexible part, such as a bellows or diaphragm kso as to obtain ymechanical control of movement and position ofthe Crown of lThorns within the magnetron. Aside from the mechanical diiiiculties ofsealing, lateral displacement and the like, that `structure also has the disadvantage, Vof enabling ythe ring gto be moved, and Aof requiring a larger end -space in the magnetron with resultant greater spacing apart of the pole pieces of the magnet than `in the usual magnetron where no Crown of Thorns is employed.

Broadly stated, then, Yan object of the present invention is to provide a tuning VIiriefnsffor a magnetron which will accomplish tuning by a Crown of Thorns construction and yet avoidthe adverse structural and operational characteristics related above.

Likewise of general nature, the inventionl contemplates operator control of internal Vtuning means but without transitional movement of mechanism from exterior to interior of the'magnetron.

More in detail, the invention has for; an object to provide a movable tuning means within va magnetron while maintaining the vprior art dimensional characteristics oi the magnetron.

Another object of the invention is'toelectrically control the functioning of :the tuning means from the exterior of the magnetron.

Yet another object of the invention is to .accomplish a rigidity of support for the :tuning means.

Other objects of the invention will appear to those skilled in the art as :the description progresses, both by direct recitationthereof and by inference from the context.

Referring to the accompanying drawings `in which like numerals of reference indicate similar parts throughout theseveral views;

Figure 1 is an axially longitudinal section of a magnetron, as on line I-I of Fig. `showing thermally operated .tuning means of the :present invention therein;

,- f' of the tuning elements in each resonantia it is within the scope of the inventionfto v'2 Figure 2 is aplan of the constructioniof-,Eig-il, but with the cover or end plateremoved;

,Figure ,3, is -a detail sectional .View lof .a,A pant Lof the magnetron as on line IIIe-.III `of ;Fig. .1 2, showing `Vring-supportingl means;

.Figure 4 is a detaill longitudinal'sectional view of oneofthe thermal elements as on line IVfIV of Fig. 5;

Figures-5 and 6 lare Vcross sectional :views of Ia thermal element within a .magnetron cavity and showing `two positions of the thermally controlled tuningmember;

Figure '7 is la sectional lview similar to E iwgml, and showing` electronic tuning Ymeans --ior the magnetron;

FigureS isa plan .of the construction ot Eig; '7, but-withthe coverforendjplate removed; and

`Figureg is a similar plan of a -fragmentalpart of the -magnetron showing the inventionas 3gpplicable to a differentshape of cavity Yof a magnetron from the conventionalsshaperof thev p r. e ceding-gures. I

In its .generalv aspects andapplicable to a1l con structions herein shown, theinvention provides xed-means within the end spacesof Vthe-Infrasinetron, here shown asrings,betweenwhich xtenda plurality of tuning elements. E aclfitl ,i g element passes longitudinally through o neothe resonant cavities of the magnetromand isshown coaxial with the cylindricalpart of such cavityin the forms using that conventional shape. The invention, however, is not limited to this coaxial relationof cavity andatuning element. Burt rmore, ywhile the present showing-shows y Qn of the tuning -elements in any number o resonant cavities desired and for range -of`A ing which the vnumber employed Swill accemp h.

`.Referringnow specifically to the, embod of the linvention illustrated the several n the reference numeral l) designates-a cylin metallic magnetron body, -theends whereof h ve cover Yor end plates lll sealed thereon thatlfthe interiormay be evacuated. vVi/ithiirand@as anintegral part of said .oody is the Vusualmagnetron anode structure I 2v rof.,general-1y lcylin d ricai4 shape but shorter than vthe. outer partof the I oody;l as to provide end spaces -|3 between-.theanode and said end plates` l-I. The anode structureis axially hollow to provide a cathode ,cavity-and. radiating from this cathode cavity are a plurality of resonantl cavities t4, -each havinginthegforms shown inFigures 1 -to8 inclusive,.aY, cylindrical portion lparallel Y to the` lcathode cavity. The-ends 3 of the cathode cavity and the ends of said resonant cavities, in all forms shown, open into the end spaces i3.

A cathode l5 passes axially through the cathode cavity, adequately spaced from the anode and supported as usual from lead-in rods I6 entering the end cavities at the sides thereof. An output loop Il is situated in one end space, likewise passing out through the side wall of the end space. The size and shape of the magnetron body, the end spaces, anode, cathode and leads above described are preferably all in accordance with prior art practice, in consequence of which the pole pieces M of the magnet (not shown) will have the same relation to the magnetron and its anode as exists in magnetrons as heretofore used.

Describing Figs. 1 to 6 more especially a ring i8 is shown concentrically situated in each end space I3, said ring being conductive and spaced from the anode, end plates, and body wall of the end space. Said ring has a position and diameter substantially locating the ring opposite the ends of the center lines of said cavities, and such that extensions of said center lines intersect the said ring at right angles to the plane of the ring. A lead-in rod i9 entering at one side of the end space, free of contact with the end space Wall, is welded or otherwise secured to the ring, and affords physical support thereat for the ring and electrical connection to the exterior of the magnetron. Said lead-in rod is introduced through a hollow housing sealed to the magnetron body and internally sealed with appropriate insulation as usual with lead-in rods of this character.

A cartridge-like tuning element, shown in detail in Figure 4, extends axially through a resonant cavity and provides axially protruding wires 2| at opposite ends, one wire being secured, as by spot welding, to one ring and the opposite wire 2l being secured in like manner to the other ring. The inner ends of said Wires 2|, within the cartridge-like element, are connected by a'heater lament 22. Said lament is surrounded by a sleeve 23 of electrically insulating material, the ends of the sleeve receiving neck portions of insulating end plugs 24 which in turn receive the said wires 2l. At the outside of said sleeve 23 next the ends thereof are metallic ferrules 25. Extending from one ferrule to the other and supported thereby is a spirally wound bi-metal thermally responsive tuning member 26. This member will change its diameter under varying heat condition, and thereby effecta change of field condition within the resonant cavity where situated. Preferably the bimetal structure is such that the spiral tuning member tends to unwind or enlarge in diameter with a rise in temperature, as indicated in Figure 6, whereas in normal position under influence of normal tube-operating condition, the bi-metal tends to wind tightly and have a minimum diameter. For tuning purposes the heater filament for the tuning member may have a current applied therethrough from the exterior by way of the lead-in rods I9, rings I8, and wires 2l, and the desired degree of heat thereby applied to the said member for expanding it the right amount. As the several heater filaments for the thermal responsive members are in electrical parallel, simultaneous tuning with respect to all cavities may thus be eiected.

In order to insure coaxial positioning of all the cartridge-like tuning elements coaxially within their respective cavities, it is preferable to retain the rings I8 in rigid and fixed relationship to the anode. For this purpose, and as shown in Figs. 2 and 3, bracket structures are provided at intervals around the rings. As shown, these bracket structures each comprise a short length of wire 21 butt welded at one end to the outer circumference of the ring, radiating therefrom and, at a short distance from the ring, bent at right angles toward the anode body. The bent end of the bracket wire is embedded in a glass bead 28 which also attaches to another Wire 29 the other end of which is embedded in and soldered to the said anode body.

It is likewise feasible to utilize the present invention to obtain field variation in a resonant cavity of a magnetron by electronic means in substitution for the above-described thermo-mechanical means. Illustrative of this modification, Figs. 7 and 8 show two rings I8 and I8a in each end space, each ring having its own lead-in rods I9 and liliL and supported rigidly by appropriate insulating brackets.

Filaments 22 extend from one ring I8 to the other coaxially through the resonant cavities, said laments in this instance being electron emissive. Around the iilaments are cylindrical grids 30 coaxial to the filaments and cavities. The grids are supported from the second ring I8a in the end space, and by virtue of the lead rod to the grid supporting ring, appropriate electrical bias may be applied to the grids.

It may be here stated that changes in emission from the tuning emissive lament, which is more generically designated a cathode, results in a change in the electron space charge density inside the resonant cavity, thereby affecting the resonant frequency of the cavity and thus changing the frequency of the generated waves from the magnetron. Thus, it is to be understood that the invention contemplates utilization of tuning cathodes as a means operable Without inclusion of the grids above-mentioned. However, the provision of grid 30 in the resonant cavity around the tuning cathode permits the space charge density to be varied much more rapidly than can be done by variation of the temperature of the tuning cathode. It is accordingly preferable to utilize said grid 3D and to vary the potential on the grid through the external lead, that variation may be rapidly and smoothly acoomplished, if so desired, the arrangement being proficiently applicable to the desired modulating operation. It will be understood that the tuning cathode would be kept negative with respect to the oscillator cavity in consequence of which the wall of the magnetron resonator cavity will act as an anode for the electrons from the tuning cathode, and so that the electrons will be aiected by passage through the grid of the tuning means.

I claim:

1. An electron discharge device comprising a cathode and anode, said anode providing cavity resonators, tuning means longitudinally disposed in a cavity resonator and projecting at opposite ends therefrom, and means constituted as a xed part of said device attached to said projecting ends of and retaining said tuning means against longitudinal displacement in said cavity resonator.

2. An electron discharge device comprising a cathode and an anode around the cathode, and having end spaces at the ends of said anode, said anode having cavity resonators opening into said end spaces, tuning means longitudinally disacume posed in a cavity.resonatorrand,projecting-at opposite ends thereof `into V:said vend spaces, and meansxin said end spaces constituted'as a-.xed part of said device attached `to said Yprojecting ends of and supporting said tunngmeans and retaining the same against longitudinal `displacement in said cavity resonator.

3. An electron discharge device comprising va cathode and an anode around the cathode, and having end spaces at the .ends of said zanode, saidanode having cavity `resonators,openingxinto saidend spaces, tuning means longitudinally disposed in a cavity resonator and projecting at opposite ends thereof into said end spaces, .and rings said end spaces supporting said tuning means and retaining the same against longitudinal displacement in said cavity resonator, said anode, cathode and ring-s having xed relation to eachother.

4. An electron Vdischarge device comprising a cathode and an anode, said anode providing cavity resonators, tuning means in each of a plurality of said cavity resonators, said tuning means each having a lament as part thereof, and means supporting the several filaments of said tuning means and electrically connecting said filaments in parallel.

5. An electron discharge device comprising a cathode and an anode raround the cathode, said anode having cavity `resonators radiating from the region around the cathode, said cavity resonators having substantially cylindrical portions axially parallel to the cathode, and substantially cylindrical tuning means in one of said cavity resonators coaxial therewith and substantially coextensive with the axial length of said cavity resonator, and said cavity resonator havinggreater cross sectional area unobstructed than obstructed by said tuning means therein.

6. A tuning means for an electron discharge device comprising a sheet-material member spirally rolled upon itself, and said member being variable in diameter by changing the tightness of rolling of said sheet material, mounting means supporting and holding one longitudinal section of said member xed, and means in proximity to said member for effecting a change in tightness of rolling of the said material of said member and thereby varying the diameter of the member.

7. A tuning means for an electron discharge device comprising a sheet-material member spirally rolled upon itself, and said member being variable in diameter by changing the tightness of rolling of said sheet material, mounting means supporting and holding one longitudinal vsection of said member fixed, and thermal means in proximity to said member for effecting a change in tightness of rolling of said material of said member and thereby varying the diameter of the member.

8. An electronic device comprising a cylindrical housing having as part thereof and within the same an anode of less length than the housing, end caps at the ends of the housing enclosing end spaces within the housing between said anode and end caps, said anode having an axial cavity and cavity resonators radiating therefrom, all of said cavities opening at their ends into said end spaces, a cathode in said axial cavity, fixed rings insaid end spaces concentric with and in planes normal to the housing axis, and electrically controlled tuning means supported by said rings `and extending through va 4plurality of said cavity;resonators.

:9. .,:Angelectronic .devicercomprising;l a cylindrical housing having as "part thereof .and withintthe same an anode of .less llength than ithehousing, end V.caps at .the Aends of the :housing .enclosing endspaces within the housingbetweensaidianode andend caps, saidanode havinganaxiallcavity and cavity resonators :radiating therefrom, all of said cavities opening at their ends into said end spaces, a cathode in said :axial cavity, fixed rings in said endspaces concentric with ,andin planesv normal to thehousing axis,brackets.:sup porting said rings from y:said anode,-,an.d :eleotrically vcontrolled tuning means supported r:by

said rings and extending through a :plurality cof.

said cavity resonators.

10. An electronic device comprising .an anode having va `housing extending beyondendsof: the anode, end caps at the ends of the, housing `enclosing end spaces within the housing between y.said end caps and the anode, said anode having :a central cylindrical cavity the ends whereof `open into said end spaces, a cathode coaxial `.toand extending longitudinally through said central cavity, cavity resonators parallel to said central cavity and opening at their ends into said. end spaces, rings in said end spaces Vconcentric -to the axis of said central cavity and crossing over the ends of said cavity resonators, and tuning means carried between a pair of rings and ,extending longitudinally of a cavity resonator, said tuning means being radially expandable lat its periphery for tuning purposes.

11. An electronic device comprising an anode having a housing extending beyond ,the ends'- of the anode, end caps at the ends of the housing enclosing end spaces within the housing between said end caps and the anode, said anode having a central cylindrical cavity the endsiwhereof open into said end spaces, a cathode Vcoaxial to and extending longitudinally throughsaidcentral cavity, cavity resonators parallel. to saidv central cavity and opening at their ends into saidend spaces, tuning means extending longitudinally of a cavity resonator and projecting into -said end spaces, and means in said end spaces ,supporting said tuning means at said ends projecting into the end spaces, said tuning means having a bimetal thermally responsive outer member `in said resonator adapted to vary the spacingof ,the said member to the cavity resonator under inuence of heat for tuning purposes.

12. An electronic device comprising a cylindrical housing having as part thereof and within the same an anode of less length than the housing, end caps at the ends of the housing enclosing end spaces within the housing between saidanode and end caps, said anode having an axial cavity and cavity resonators radiating fro-m the axial cavity, all of said cavity resonators opening at their ends into said end spaces, a cathode in said axial cavity, rings in said end spaces concentric with and in planes normal to the housing ,axis, brackets supporting said rings from -said anode. said brackets having means insulating the Yrings from the anode, and tuning means supported by said rings and extending through arplurality of said cavity resonators, said tuning -means ycomprising a bimetal thermally responsive outer member and an internal heater therein.

v13. An electronic device vcomprising a cylindrical housing having as part thereof :and within the same an anode of less length than-thehousing, end caps at the ends-of the housing enclosing end spaces within the housing between saidzanode andend caps, said janode having fan-axial-icavty and cavity resonators radiating from the axial cavity, all of said cavity resonators opening at their ends into said end spaces, a cathode in said axial cavity, rings in said end spaces concentric with and in planes normal to the housing axis, brackets supporting said rings from said anode, said brackets having means insulating the rings from the anode, and tuning means supported by said rings and extending through a plurality of said cavity resonators, said tuning means comprising a heater surrounded by an expandable thermally responsive outer member expansion whereof brings it closer to the wall of the cavity resonator.

14. A magnetron comprising an anode having a central cavity and a plurality of cavity resonators radiating from said central cavity, a first electron-emissive cathode in said central cavity, leadin connections connected with and for applying operating potentials to said anode and cathode to generate microwave oscillations on said anode, a second electron-emissive cathode in one of said plurality of cavity resonators opposed to a part of said anode for also directing electrons to the anode, and for thereby modifying the said microwave oscillations.

15. A magnetron comprising a iirst electronemissive cathode and an anode disposed adjacent said cathode, means connected with and for applying operating potentials to said anode and cathode and thereby obtaining electron flow on paths from the cathode toward said anode to generate microwave oscillations on said anode, a second electron-emissive cathode opposed to another part of said anode for also directing electrons to the anode but to said other part thereof on paths other than the aforesaid paths of electron ow, and for thereby modifying the said microwave oscillations, and means in the path of and for controlling the electrons emitted from said second cathode.

16. A magnetron comprising a first electronemissive cathode and an anode coaxially disposed adjacent said cathode, means for applying operating potentials to said anode and cathode to generate microwave oscillations on said anode, a plurality of second electron-emissive cathodes distributed in a coaxial series around the first said cathode and opposed to said anode for also directing electrons to the anode, and for thereby modifying the said microwave oscillations, and means around each of said plurality of second cathodes for controlling the eiectrons emitted therefrom.

17. A magnetron comprising a first electronemissive cathode and an anode coaxially disposed adjacent said cathode, means for applying operating potentials to said anode and cathode to generate microwave oscillations cn said anode, a plurality of second electron-emissive cathodes distributed in a, coaxial series around the first said cathode and opposed to said anode for also directing electrons to the anode, and for thereby modifying the said microwave oscillations, all of said second cathodes being connected in parallel, and a lead-in in connection for said plurality of parallel-connected second electron-emissive cathodes.

18. A magnetron comprising an emissive cathode and an anode disposed around the cathode, said anode having cavity resonators therein opening toward the cathode and having partitions directed edgewise toward the cathode and separating successive resonators from each other, means for applying operating potentials to said anode and cathode to generate microwave oscillations on said anode and in said resonators, and means in each of a plurality of said resonators for varying the capacitance thereof and for thereby modifying the said microwave oscillations.

19. A magnetron comprising an emissive cathode and an anode disposed around the cathode, said anode having cavity resonators therein opening toward the cathode and having partitions directed edgewise toward the cathode and separating successive resonators from each other, means for applying operating potentials to said anode and cathode to generate microwave oscillations on said anode and in said resonators, and a plurality of second electron-emissive cathodes of which one is in each said resonator for directing electrons to adjacent partitions for varying capacitance of the resonator and for thereby modifying the said microwave oscillation.

20. A magnetron comprising an emissive cathode and an anode disposed around the cathode, said anode having cavity resonators in a series surrounding and opening radially toward the cathode, said anode having partitions on radii from said cathode directed edgewise toward the cathode and separating the successive resonators of said series from each other, means for applying operating potentials to said anode and cathode to generate microwave oscillations on said anode and in said resonators, and means in each of a plurality of said resonators of said series for varying the capacitance thereof and for thereby modifying the said microwave oscillations, said capacitance-varying means of each resonator being isolated from the others thereof by said partitions.

21. A magnetron having an elongated cathode and an anode around the cathode, said anode having cavity resonators radiating from the region around the cathode and having longitudinal openings into said region parallel to said cathode, each cavity resonator having lateral walls symmetrically disposed on opposite sides of a medial plane longitudinal of the opening and radially of the cathode, tuning means in a cavity resonator substantially coextensive with the length of the resonator and medially between said lateral walls thereof and in said radial plane and in parallelism to said cathode, and a support for said tuning means retaining the same in longitudinally fixed position in its cavity resona- 22. An electron-discharge device comprising: a cathode; an anode, incorporating a cavity resonator, spaced from said cathode; means, adjacent said anode, for establishing a unidirectional magnetic field in said cavity resonator; and means, incorporated in said device, for projecting a stream of electrons into said cavity resonator to control the resonant frequency of said device.

23. An electron-discharge device comprising: a cathode; an anode, incorporating a cavity resonator, spaced from said cathode; means, adjacent said anode, for establishing a unidirectional magnetic field in said cavity resonator; and means, incorporated in said device, for projecting a stream of electrons into said cavity resonator in a direction transverse to that of said magnetic eld to control the resonant frequency of said device.

24. An electron-discharge device comprising: a cathode;A an anode, incorporating a cavity resonator, spaced from said cathode; means, adjacent said anode, for establishing a unidirectional magnetic eld in said cavity resonator; means,

incorporated in said device, for projecting a stream of electrons into said cavity resonator to control the resonant frequency of said device; and means, coupled to said last-named means, for varying the density of said stream of electrons to frequency modulate said device.

25. An electron-discharge device comprising: a cathode; an anode, incorporating a cavity resonator, spaced from said cathode; means, adjacent said anode, for establishing a unidirectional magnetic eld in said cavity resonator; means, incorporated in said device, fer projecting a stream of electrons into said cavity resonator in a direction transverse to that of said magnetic eld to control the resonant frequency of said device; and means, coupled to said last-named means, for varying the density of said stream of electrons to frequency modulate said device.

26. An lelectron-discharge device comprising: a cathode; an anode spaced from and surrounding said cathode; said anode including a plurality of radially disposed anode arms each pair of which, together with that portion of said anode lying therebetween, denes a cavity resonator; means, adjacent said anode, for establishing a unidirectional magnetic field through said cavity resonators in a direction transverse to the discharge path between said cathode and said anode; and means, communicating with one of said cavity resonators, for projecting a stream of electrons therein in a direction transverse to that of said magnetic field.

27. An electron-discharge device comprising; a cathode; an anode spaced from and surrounding said cathode; said anode including a plurality of radially disposed anode arms each pair of which, together with that portion of said anode lying therebetween, denes a cavity resonator; means, adjacent said anode, for establishing a unidirectional magnetic eld through said cavity resonators in a direction transverse to the discharge path between said cathode and said anode; means, communicating with one of said cavity resonators, for projecting a stream of electrons therein in a direction transverse to that of said magnetic field; and means coupled to said last-named means, for varying the density of said electron stream.

28. An electron-discharge device comprising: a cathode; an anode spaced from and surrounding said cathode; said anode including a plurality of radially disposed anode arms each pair of which, together with that portion of said anode lying therebetween, defines a cavity resonator; means, adjacent said anode, for establishing a unidirectional magnetic field through said cavity resonators in a direction transverse to the discharge path between said cathode and said anode; and an electron gun, carried by said anode and cornmunicating with at least one of said cavity resonators, for projecting a stream of electrons therein a direction transverse to that of said magnetic eld.

29. An electron-discharge device comprising: a cathode; an anode spaced from and surrounding said cathode; said anode including a plurality of 10 radially disposed anode arms each pair of which, together with that portion of said anode lying therebetween, denes a cavity resonator; means, adjacent said anode, for establishing a unidirectional magnetic iield through said cavity resonators in a direction transverse to the discharge path between said cathode and said anode; an electron gun, carried by said anode and communicating with one of said cavity resonators, for projecting a stream of electrons therein in a direction transverse to that of said magnetic eld; and means coupled to said electron gun, for

`varying the density of said electron stream.

30. An electron-discharge device comprising: a cathode; an anode spaced from said cathode; said anode including a pair of anode arms which, together with that portion of said anode lying therebetween, denes a cavity resonator; means, adjacent said anode, for establishing a magnetic eld through said cavity resonator in a direction transverse to the discharge path between said cathode and said anode; and a source of electrons, communicating with said cavity resonator and adapted to project electrons therein, for altering the resonant frequency thereof.

31. A tunable electron-discharge device comprising: a cathode; an anode structure spaced from said cathode, and incorporating a cavity resonator in which radio-frequency oscillations are adapted to be generated; means adjacent said cavity resonator for establishing a magnetic eld therethrough; means, cooperable with the electric-eld component of said radio-frequency oscillations, and with said magnetic eld, for setting up a space charge in said cavity resonator; and means, coupled between said cavity resonator and said last-named means, for varying the density of said space charge.

JOHN W. MCNALL.

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

UNITED STATES PATENTS Number Name Date 2,027,521 Drake Jan. 14, 1936 2,079,809 Kuhle et al May 11, 1937 2,163,157 Samuel June 20, 1939 2,241,976 Blewett et al May 13, 1941 2,338,237 Fremlin Jan. 4, 1944 2,348,986 Linder May 16, 1944 2,356,414 Linder Aug. 22, 1944 2,408,234 Spencer Sept. 24, 1946 2,408,817 Snow Oct. 8, 1946 2,408,903 Biggs et al Oct 8, 1946 2,409,038 Hansell Oct. 8, 1946 2,411,984 Brown Dec. 3, 1946 2,414,496 Varian Jan. 2l, 1947 2,443,179 Benioi June 15, 1948 2,480,462 Garbe Aug. 30, 1949 2,498,763 McNall Feb. 28, 1950 FOREIGN PATENTS Number Country Date 537,518 Great Britain June 5, 1941