US2582185A - Cavity resonator magnetron - Google Patents

Description

Jan. 8, 1952 w. E. WILLSHAW CAVITY RESONATOR MAGNETRON Fild Aug. e, 1947 Patente-2d Jan. 8, 1952 CAVI'EY RESONATOR MAGNETRON Wiiiiam Ernest Wilishaw, Kenton, England, as-

signozr t0 The M-O Valve Company Limited,

Landau, Eingland Appliczwtionlngus 6, 1947, Serial N01, 766,756 In Great-Britasin May 171946 Secaion 1, Puh'ic Law 690, August 8, 1946 Pa's-encaxpistes May 17, 1956 6 Chinas. 1

This. invention relaces 150 apparatus f0r am" plifying or multiplying the frequency of electrical oscillations 0f high frequeney, espgcially but not exclusively, of frequency as high as er higlzer than 3000 megacycles per second.

One of the most efiective forms of appai*atus Which. has been developed for generating electrical. oscillations of' very high frequency is the magnetron escillator, and the object of this inventionis to adapt for 'she purpose cf ampl'ifying and. frequency multiplying, flne principles 021 which the magnetron depends .for the generation o1 oscillations.

In the we1l known magnetron oscillator in which a cylindrical cathode is surrounded by a ring of hollow res'onators, energy is transferred from d'ireet current fiel'd to an oscillatory fie1d. by the reaction of electrons energised by the direct oz:urrent fieldwith the oscillatory fields Withitn.

the hollow resonators a magnetio fie1d app1ied transversely of the direct current fiel d ensuring that electrons which receive energy from the oscillatory fie1ds are immediacely returned so the cathode whereas electronswhich give up energy to the oscillatory fie1ds trave1 round the cathod in synchronism With a potential wave travelling round the resonators so that these electrons give up energy to a plura1ity of resonators in succession.

According 110 the present invention a magfor density modulating said stream in acc0rdance with the amplitude and frequency cf Ehe input oscillation, electrod'es defining an electron orbit space along which said density mndulated stream can fiow under the influence 033 an electrostatic field between sa.id electrodes amd a transverse magnetic field, a. plurality of coupled resonant output circuits spaced apart along said electrrm orbit. space so as 130 Tue excitable in succession by said density modulated. stream 2md resonant as a whole at a frequency n f, where n is an integral number and f is the frequency of the said: inm1t oscillation, and means for extracting the required output oscillation from the said output circuits. For an amplifler n equals one and for a frequency multiplier n is an integer greater tha,n one. For frequency-multiplying the density modulation o1 the electron stream must be nonsinusoidal.

The successive excitationof the ou-tput circuits sets up a system of potential variation having a travelling wave component which, With the resonanti output circuits spaced in accordance With the mean velocity of the. electrons is synchronised With the flow of the electrons so tha.t a considerable transfer of energy is obtained and a streng outpu1; oseillation built up.

The term resonant output circuits is used instead of hollow resonators since the resonators might in some cases be replaced by resonant fingers or possibly by physically distinct resonant output circuits connected across s1its between adjacent anode segments.

In general, and especially for very high frequency use, all the electrodes and circuits will be enclosed within or form part of the Walls of the evacuated enclosure in which the electrons are adapted to move, but in some cases parts of the apparatus, and especially parts of fihe input and output circuits; may be locat'ed' or extend out'side the Walls of' the enel0sure;

It may also be noted' that' the output circuits need not be individually resonant at t11e frequency, er an integral multiple of the frequency, of the input oscillaoion so l'ong as the' combined output circuit formed by the co'upling tcgeher of the individual output circuits is eifectively resonant at' the required' output frequency; thus the rising sun arrangement often used in resonant cavity magnetronsmay be adopted toensure wicle mode-spacing.

The coupling together of the output circuits Will in general be effected merely' by their dis position, but in somecasesspecial couplirigmaatls may be used. Thema must, of course, be substantially nocoupling between the oufiput circuits and the input circuit 01" the system may be se1f oscillating and not function zus an aniplifier er frequency multiplier.

Further it' may be noted that, with other forms 0f amplifier; the apparatu.s ma=y have utility even if the amplitude cf theoutput oscil- Iation is lass than that of the input oscillation; accordingly it Will be understood that in; this specification the: term 'amplifying does nt necessarily i'mp1y that the output' oscillation. is of greater amplitude than tbe input Gscixllation a1though this Will often be the case.

The preferred method. of producing an densiy modulated stream of electrons in apparatus in accordance with the invencion is so arm-rage a thermionic cathoe opposite an input circuit which is excitable by and resonant at the fre quency of the input oscillation .s0 that the emission from the cathode: isscontrolled by the inpuo cirouit anct 150 arrange: a non-secondarily emissive electron-intercepting electrode adjacenl; 130 the cathode so that by the applicatlon of crossed electrostatic and magnetic fields, which may be the same as those applied in the electron orbic space, the electrons emitted from the cathocle are directed to the intercepting eleccrode in the absence of any input oscillation; then when the input oscillation is applied electrons which are retarded by the input circuit are diverted from the intercepting electrode and fiow on to excite the output circuits along the electron orbit space, the effect being that isolated groups of electrons are released 110 the electron orbit space, the number of electrons in each group corresponding to the amplitude of the input oscillation and the spacing between the groups corresponding to the frequency of the input oscillation; the spacing between the output circuits is arranged 130 be half ehe spacing between the group of electrons. This method of density modulation results in a non-sinusoidally modulated stream Which is well suited for frequency multiplylng.

It Will be appreciated that either amplifying er frequency multiplying apparatus in accordance With the invention need not be of the circular form simllar to the well known magnetron osclllator; a linear form in which the cathode eleo trode and a co-operating anode electrode are substantially plane may be usecl; but the clrcular form is preferred and one embodiment of the invention in this form, which is an amplifier, will now be described by way of example with reference to Figures 1 and 2 of the accompanying drawing.

Figure 1 shows a section at right angles to the circular axis and Figure 2 a section comtaining the circular axis; the section of Figure 2 is in the plane 22 of Figure 1, looking from the right, and the section of Figure 1 is in the plane II of Figure 2, also looking from the right.

In this embodiment, the apparatus comprises a cylindrical metal block anode l recessed als each end face to leave an annular peripheral flange 2 and pierced co-axially by a cylindrical hole 3 which provides the electron orbit space. Around one half of this hole the block ls further recessed deeply ab each and face to form a thinner semicircular rlng 4 which is pierced parallel 110 the axis by eight holes 5, each communicating with the hole 3 through a radial slot 6 pieroed through the ring 4 parallel 170 the axis, and, each adl'acent to the thicker part of the block, two semi-circular holes 1 each communicating with the hole 3 through a slot 8 of half the width of the slots 5.

The holes 5 and slots 6 constitute output cavities each resonant at the frequency at which the apparacus is adapted to operate, that is amplify, and the holes l and slots 8 likewise constitute cavities resonant als the said frequency; these last two cavities are shaped so as to have zero field along the face of the thicker part of the block so avoicl coupling with the input circuit.

Near the centre of the thicker part round the central hole 3, the block is pierced parallel to the axls by two radial slots 9, each of radial length effectively one quarter of the wave-leneth at which the apparatus is adapted 130 operate and between the slots the block is recessed from each end face toform a wedge-shaped finger lll, resonant at the said wave-length, having the same axial thickness as the ring 4; the finger 10 constitutes the resonant input circuit.

Along the centre of the hole 3 there is located, coaxially, a cylindrical cathode electrode II which is carried by clrcular end plates I2 each supported by a stout meoal lead I3 s'ealed through the cylindrical wall of the block by a metal-t0- glass thimble seal I4 in accordance with the technique usual in magnetrons. The surface of the cathode elecorode II is treated to render it everywhere substantially non-secondarily emlssive, Tor example by coating with titanium dioxide.

At about the centre and to one side of the finger I0, the cathode electrode l l and end plates l'2 are cut away accommodate an indirectly heated primary cathode I5 consisting of a metal box containing a heater I5; the ourved outer face of the box, which face is coated wioh electron emissive material, ellectively forme a 00mpleti0n cf the cathode electrode cylinder.

The primary cathode is carried by end plates I! each supportecl by a stout metal lead I8 sealed through the cylindrical wall of the block by a metal-to-glass thimble seal l9; the leads 58 serve also as current supply leads to the healser I6 and the primary 'cathode is insulatecl from the cathode electrode so that the two electrodes can if required be maintained ab different potentials by means of the leads I8, l3 respectively.

Between the primary cathode !5 and the adjacent cavity constituting the hole l and slot 8 but nearer the cathode I5, a metal strip 20 is set, parallel the axis, into the block bounding the cylindrical hole 3 and extends radially to within a short distance of the cathode electrode II; the strip 20 constitutes an electron barrier preventing electrons from re-passing the flnger I0.

An input lead 21 so the finger H] is sealed through the cylindrical wall of the block by a metal-toglass thimble seal 22, and an output lead 23, terminating in a loop lying within one of the holes 5, is sealed through alle wall by a metal-to-glass thimble seal 24.

The resonant cavities formed by the holes 5 and slots 6 constitute the resonant output circuits adapted to be excited by electr0ns moving round the electron orbit space 3, and Ehe metal tongues formed between adjacent slots are connecoed together, a1; each face of the block, by metal modespacing straps 25, 26, sei: into circular slots formed in the tongues, of which on one face of the block strap 25 connects together the odd numbered tongues, that is to say the first, t'nird, fifth, seventh and nlnth tongues, and strap 26 connects together the even numbered. tongues, that is to say the second, fourth, sixth and eighth tongues, counting round the block, whilst on the other face of the block the outer strap 25 connects the second, fourth, sixth and eighth tongues whilst the inner strap 26 connects the first, third, fifth, seventh and ninth tongues. The spacing between the resonant output caviales is arranged relative to the electro static and magnetic fi8lds 130 be used to correspond to the mean velooity of the electrons round the electron orbit space so that the distance between successlve resonators is half the length occupied by a complete cycle of electron density variation.

T0 each face of the shallow recess from Which the fianges 2 project is screvved. a potentialequalising platze 29 and the block ls sealed off by means of end-plates 21 attached to the fiange 2 in accordance with the usual magnetron technique.

The apparatus is evacuated and finally sealed oft by means of a pumping lpube 28 sealed to the glass thimble of one of the cathode electroole lead seals.

For amplification of an input oscillation of frequency 3000 megacycles per second with apparatus relatively dimensioned as shown, the radius of the block I should be about two inches.

I claim:

1. A magnetron device comprising an anode electrode and a parallel cathode electrode defining between them an ended electron Orbit space, means for producing a stream of electrons originating ab one end of said space ancl flowing along the space, means for receiving a high frequency input osclllation, means for density modulating said electron stream at saicl end of saicl space in accorclance with the amplitude and frequency of the input oscillation, a plurality of resonant output circuits connected across slots formed in said anode electrode and spaced apart along said electron o1bit space so that said circuits are excitable in succession by said density modulated stream of eleotrons and resonant as a whole a1: a frequency n f, where n is an integral number and f is the frequency of said input oscillation, and means for extracting the required output oscillation from said output circuits.

2. A magnetron device as sei: forth in claim 1 which functions as an amplifier wherein n equals one.

3. A magnetron device as sei; forth in claim 1 which functions as a frequency multiplier Wherein n is an integer greater than one.

4. A magnetron clevice comprising a metal block anode electrode and a parallel cathode electrode defining between them an ended electron orbit space through which electrons can flow under the influence of an electric field applied between said electrodes and a transverse magnetic field, said anode block being recessed at one region 120 form an input cavity system resonant ab frequency f and ab another region well spaced along the electron orbit space from said first region being recessed to form a plurality of mutually coupleol resonant cavities arranged in succession along the electron orbit space to form an output cavity system resonant at frequency n f, where n is an integral number, a thermiom'c cathode whose electron emissive surface occupies a restricted region of said cathode electrode lying opposite said input cavity system, input means for applying an input oscillation to excite said input cavity system at frequency for controlling the flow 01 electrons from said cathode, and entput means for extracting from said output cavity system oscillations of frequency n f excited by the fiow of electrons through said (alectron orbit space.

5. A magnetron devica comprising a cylindrical cathode electrode containing a thermionic cathode whose electron emitting surface extends axially along the cathode electrode surface but occupies only a smal1 circumferential width thereof, a cylindrical metal block anode electroole lying concentric With but spaced from the cathode electrode oo form between them the magnetron electron orbit space, at least one s1ot extending axially through the anode block at a region thereof opposite said electron emissive surface to form an input cavity system resonant a1: a frequency f for controlling the emission of electrons from said cathode, a plurality of adjacent slots each extending axially through the anode block over a restricted region thereof well spaced angularly from the input cavity system to form an output cavity system exeitable by electrons fiowing from the saiol cathode through the electron orbit space under the infiuence of a radial electric field between the anode and cathode electrodes anal an axial magnetic field and resonant at frequency n f, where n is an integral number, an electron barrier electroole extending radially between said anode and cathode electrodes at a region between said input and output cavity systems for preventing repeated circulation of electrons round said electron orbit space, input coupling means for excioing said. input cavity system a1: frequency f, and output coupling means for extracting an output 0scillation of frequency n f from said output cavity system.

6. A magnetron device according claim 5 wherein the slots in the output cavity system define metal tongues, and wherein said tongues are connected together on each side of the block by two conductive mode spacing straps of which one strap connects together the odd nurnbered tongues and the other connects together the even numbered tongues, counting around the anode block.

WILLIAM ERNEST WILLSI-IAW.

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

UNII'ED STATES PATENTS Number Name Date 2411953 Brown Dec. 3, 1946 2,412772 Hansell Dec. 17, 1946 2412824 McArthur Dec. 17, 1946 2414085 Hartman Jan. 17, 1947 2416298 Fisk Feb. 25, 1947 2418117 Hale et a1. Apr. 1, 1947 2423716 McArthur July 8, 1947 2429291 Okress Oct. 21, 1947 2437279 Spencer Mar. 9, 1948 2487656 Kilgore Nov. 8, 1949

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