US2402397A - Ultra short wave oscillator - Google Patents

Description

C. w; HANsELl.

ULTRA SHORT WAVE'OSCILLATOR Filed July 25, 1941 June' i8, i946.

lNvENToR Wha/ABZ@ BY Z WW ATTORNEY Patented June 18, 1946 fiom-TED STATES *PATENT lOFiFfl-CFE' K 2,402,397 vlurfrimf SHORT WAVE oscmm'roa `Clarence WmHansell, Port-Jeuersony- Y.,as signor to Radio Corporationof.America,=a.cor

poration vof A.Delaware Application-"-Jilly'li 19441, Serial No.`l 403,985

, Claims.

.This'invention relatesftdelectronzdischargegdevicelapparatusg-and 'moreparticu'larly toa-masnetron oscillator: fori :the-generation; of zultra high fre quency: waves.

An object ofrthef.present.iinventionris toprovide an electron discharge device oscillator having a completely enclosed anode circuit formed by a plurality of physically spaced anode seg- -ments 'whovse"circi1ri'1ferential` length-has a' particular `relation i-to' the 'frequencyfof I operation.

Anther- 'object f Tthefpresent invention isto provide` a splitanodeI oscillator :wherein the width ofthe gaps between the adjacentanode'fisegments and"the' natural` period" of lcircumierential Loscillation of v'the anode structure," taken together with '1 the magnetic "eld and #potential adjustments,

control the frequency 'of oscillations.

`It hasl been customary' -in thepastfto employ magnetron oscillators of the split anode\type Whereinthe Ianode-'segments 'operate inpushpull relation to each other. "'Insuch'fknown mag- `netron'oscillators,v each` anode-l segment =has for its entire circumferential --length 'one -instantaneous potential,A andthe normal '-mo'de of loscillation is vgovernedbytheeconstants of the-fex ternal tuned'circuits' and thefadjustmentsfof the magnetic field, as Well as by the-anodeivoltage.

vlin these oscillators; the circumferential length of the anode-segments bears no especial relation to the wavelength or 'frequency 'of' operation. 'iThe f improved; magnetron oscillator of `the present invention, however,"employsfa v5new mdef-*oscillation which obviatesl the 'need'orexternal tuned circuits for the anode' structure. lf-By constructing the 'anode segments of my improved oscillator sol that theI circumferential length thereof bears 1a desired relation tothe wavelength or frequency of operation, I amiablefto obtain oscillationsin a" circumferential *direction around the anode structure. In the oscillator ofthe inventiomthe circumferential 'length ofeach anode' segment isv electrically' one-half Wavelength'A -for 'one'4 mode of oscillation, or multiples of one-half wavelength off'other modes of""os`cilla'tion. "The Icircumferential 'portions of v'ftl-iefandefsegmentsftl'ius ldefine inductancesfwhile the'` gaps" between-@thei'ande segments form capacitances "which Vtogether-provide f a" primary influence' upon thefrequency of oscillations. 'A secondary'ini'luence ini determining the"'frequency"f oscillations of myfoscill'ator is the' V'electron-1velocity irrithe'region of thefgapsy @which is dependent upon'thev anode 1 potential re1- lative tothecathodeionfilament o .-By'V employing 1fcircumferentialfroscillationsthe u oscillatorzrof` the-invention providessa veryzwide f .sociated X kconnecting leads.

1o off. operation than invknown types ofrmagnetron .oscillators lwhich do. not employ circumferential oscillations.

' One:4 advantage i ofthe. osc'zillatorv of/therfinvention-liesin -lthe'l' fact 'that it.:is:possiblet-to obtain l. oscillations by 'virtue'. ofeelectron travel over-:dis-

tances .Which arewquiteshorttcompared: toi-the wavelengths` soL-.thatfvthe.electron velocitiesiand anode :Voltage: required: for a, given --wavelength may Yjbe yvery; muchfless thany 'inother .ty-pes; of

oscillators.

.'Avfeature of. the A`invention residesxin the: fact 4 that :the:` electrons :circle "the: Yfilament in one .direction'v only, and; impinge upon onlyv oney endxof each anode segment. vAnother feature lies 4inathe *use-of means.-emp1oyed for preventing-.electrons Yemanating. from thelament. or cathode .fromidisjfpersing inwrong directions. In .this way; I; am .able-toreducef emission of those electronswwhich do not '-aid': in producing vcircumferential oscil- A latOIlS.

- A' more detailed 'description fof: the invention lfollows Vin conjunctionwith-1: a .'drawing, wherein: ,-Fig.A lfshoWsv incrosssection a view,` oi". the essential-4 features A of 'f a split-r anode magnetron-os- 35 cillation,A generator of the invention,` the. arrows diagrammatically; representing the; paths vtaken .by J'the l.electrons under different conditionsrzof operation;

.2.schematically, shows 'the embodiment: of

40 Fig. 1 in a-.completecircuitr arrangement;

Fig.y 3 is f a detail showing an' alternative Iform offilament orI cathode for :preventing electrons from Vdispersing` inrfwrong directions;

vFigli ist amodication ofthe oscillatonof'Fig.

.1- showing how l more than twof anodeasegments can-be employed-in` an anode structure and Fig.- 5 .is aview in crosssection. of- -the oscillator of: theinvention provided withA .a preferred f form of anodeconstruction.

The oscillation generator shown-in Fig; loom- 'prisesanfevacuated envelope l made of: anysuitf 1 ablefmaterial'suchfasf glass, Vcontaining Ewithin it azcentrally located linear kelectron "emitting cath- 'ode 2, :andian:.anodeistructurel composed of Ia pair of spaced or split anode segments 3A Saeach 3 of which has a circumferential dimension which is electrically one-half wavelength long for the lowest mode of oscillation. These anode segments may be a multiple of a half Wavelength long in a circumferential direction for other modes of oscillation. The relation of the circumferential dimension of each anode segment to the Wavelength is indicated in the drawing. A eld coil 4, which may or may not employ iron to aid its effect, surrounds the envelope and functions to produce an intense but constant magnetic eld which has flux lines runningthrough the envelope in a direction parallel to the cathode 2 so as to influence the movement of the electrons emanating therefrom. Grid wires 5, 5 serve to reduce electron emission from the cathode 2 in those directions which do not aid in the produc- These grid tion of circumferential oscillations. wires are maintained at near zero or negative potential relative to the cathode 2. Both anode segments 3, 3 are of equal length and are maintained at rthe same positive direct current poten- Y tial relative to the cathode;

As is Well known, the electrons which ordinarily tend to move in radial lines from the cathode, when subjected to the action of a magnetic eld from coil 4 in a direction parallel to the cathode, or at right angles to the electric field between the electrodes and to the paths of the electrons, will tend to move in a spiral line tangentially to the anodeV as indicated by the arrows of arcuate paths X and Y. As the strength of the magnetic field is increased, these spiral lines contract toward the cathode, and if the field is made strong enough, it will be apparent that substantially none of the electrons will reach the anode segments. If the strength of the magnetic eld is decreased, however, substantially all of the electrons can be made to reach the anode. In the present invention, the field strength and the value of the positive direct current potential applied to the anode segments 3, 3 are adjusted to a critical value so that the electrons just skim past the ends of the anode segments and follow either the path X or the path Y, depending upon the instantaneous potential of the ends of the anode segments. The electrons, it should be noted, will strike or come close to a negative anode end A or D when the adjacent ends C or B have a potential momentarily in excess of the positive applied direct current potential; a posteriori, the electrons will not reach or come soclose to ends A and D when the adjacent ends C and B are less positive than the applied direct current potential. It will be evident that the potential uctuations of the anode edges A and C, and B and D control the paths of electron motion. Since points A and C, and B and D have a potential 180 out of phase,'and the two anode segments are electrically closely coupled together, we thus have conditions which can maintain oscillation.

In the production of oscillations, high fre quency fluctuations in potential between adjacent ends of the anodes cause :fluctuations in paths taken by the electrons in a manner to increase the potential fluctuations up to a limiting value. Many electrons strike on or near portions A and D but a large number of the electrons ily in the curved path X and return to the cathode. The oscillating currents in the anodes give lrise to fluctuating or oscillating magnetic eld strengths in the space between cathode and anodes 'and this also may contribute to the control of electron paths and aid in the production of oscilla tions. j

It should be noted that the electrons circle the cathode 2 in one direction only and hence there is only one end of each anode segment A or D upon which the electrons impinge. Since anode segments 3, 3 are each a half wavelength long electrically, or a multiple thereof, depending upon the mode of oscillation employed in the operation of the device, there will be a. wave propagated around the anode structure whose resonant period is determined in part by the circumferential dimensions of the anode segments and the spacings therebetween, and in part by the electron velocity in the region of the gaps between the anode segments, in turn dependent upon the anode potential relative to the cathode. Assume, by way of example, that the distance between adjacent edges of the anodes is 0.25

centimeter, then the portion of electron path most active in producing oscillations may be on the order of 1 centimeter. The anode potential, which may be applied in short pulses, may be 25,000 volts, corresponding to electron velocities of 9 109 centimeters per second. The time required for each electron to pass through the 1 centimeter active region will then be second. If this time is allowed to be no greater than say 0.1 of thetime of one cycle of oscillation, then the frequency of oscillation will be 900 megacycles. For thecase assumed, this would likely be the frequency at which transit time effects begin to reduce the efficiency and strength of oscillation as the frequency is increased but it is not the highest frequency for which oscillations may be produced for this mode of oscillation, when the anodes are properly dimension for resonance.

Other higher frequency modes of oscillation are obtainable corresponding to elfective time delays of 1, 2, 3, 4, etc., cycles of oscillation for electrons to pass through the active space between ends of the anodes. Thus, there is a series of modes of oscillation obtainable according to physical dimensions and intensity of electric and magnetic fields.

Fig.2 illustrates how the oscillator of Fig. 1 can be embodied in a complete circuit arrangement. It should be noted that anode segments 3, 3 are of equal length and have equal circumferential dimensions. In order to supply the anode segments with a positive direct current polarizing potential relative to the cathode, there are provided quarter wavelength leads 6, 6 which join the ends of the anode segments to the positive terminal of battery 1 through radio frequency choke coils 8, 8. The lengths of the leads 6 are such that there is provided a high impedance at the points thereof joining the anode segments for energy of the operating frequency. A radio frequency by-pass condenser 9 bridges the ends of leads 6, 6 at the location nearest the choke coils 8, 8. For deriving output energy from the oscillator, there may be provided a loop I0 which can couple inductively with the leads 6, 6 at a suit able point intermediate its ends. Obviously, output energy may be obtained not only by the output coupling loop I0 but* also by electromagnetically coupling a loop or open-ended con-` densers to one or both of the anode segments 3, 3. Further, the nature of the oscillator is such that it can radiate energy directly, for which reason it can, if desired,fbe mounted in front of a reector to provide directivity of radiation. It

fag-rogge? trcmagnetically shielded.

odeisf coated with electroni emissive'v material at f twoA points l i, H info-r'der -to preventelectronsv f-rornl-dispersing in thelwrong.l directions. Obviously; if f fthecathode of Fig oscillator of Ythe raven-ums?.therewilll `be nef-need f for employing grid wires 5; 5.A Y

Fig.fl4 shows, 'informs-section, an oscillationA generator which `is a modification-of the-'oscillator offiFig.' 1, differing therefrom; mainlylinl-the-use' of ani-additional' i anode-segment. ''It will? thus be evident' that' the anode-segments are `*not `limited td two, as-shown Figbbut may be increased in number to three, as shown in Fig. 4, or any desired number provided the desired relation of circumferential length and resonance frequency to wavelength of operation is followed. It should be noted in Fig. 4 that here again the electrons.. circle the filament in one direction only. To reduce electron emission from the cathode in undesired directions, there are now employed in Fig. 4 three grid wires 5', 5 which are maintained at zero or negative potential relative to the cathode. If desired, a cathode similar to that shown in Fig. 3 may be employed in Fig. 4 with the modi-f cation that the cathode be coated at three equally spaced points circumferentially thereof, in order to furnish electron emission at the desired locations, in which case it will not be necessary to employ the grid wire 5', 5.

Since, for `the type of operation described, electrons impinge principally on or near one edge f each anode segment, this edge will have greatest..

heating. As an aid to disposing of this heat, and to lengthen the anode life when very high potentials are used, I contemplate increasing the thickness of metal at and near this edge after the manner described in my United States Patent No. 2,037,977. Fig. shows a fragmentary View of an oscillator of the invention with the' anode segments of greater mass at the portions predominantly struck by the electrons.

What is claimed is:

l. Electron discharge apparatus comprising a linear cathode, a self-contained oscillatory circuit comprising a plurality of spaced anode segments surrounding said cathode, the circumferential length of each of said anode segments being electrically one-half wavelength for the lowest mode of oscillation and said circumferential portions dening inductances, the spaced portions of said anode segments forming capacitances in circuit with said inductances.

2. An electron discharge device oscillator comprising a linear cathode, a self-contained oscillatory circuit comprising a plurality 0f spaced anode segments of equal circumferential length surrounding said cathode, the circumferential length of each of said anode segments being electrically a multiple, including unity, of one-half wavelength for a mode of oscillation and said circumferential portions defining inductances, the spaced portions of said anode segments forming capacitances in circuit with said inductances, whereby there are Obtained oscillations in a circumferential direction around said anode segments.

3. An electron discharge device oscillator comprising a linear cathode, a plurality of spaced anode segments surrounding said cathode, the

circumferentmnengths.:en said :anode segments l prising a'ilinear cathode, vva plurality vf spaced i'ande iksegments surrounding f said cathode, the l circu'niferen'tial"v lengths' :off 'said' `,anode segments having "flux ilinesf'finl adirectionllparallel to f said cathode, '-the circumferential 'portions-of said anode segments dening inductances,-the spaced l"portions :fsaid anodesegments forming capacitancesin circuit withsaid inductances,. v

l 4; An y"electron discharge' device oscillator' combeing a multiple; including-unity, of' a half-wavelength long 'fora/'desired 'mode of '.oscillation,

'-nieans -forprodu'cingea'l constant magnetic i field "cathOde, lthe f circumferential lportions '#cf'fsaid tive to said cathode for controlling the electron emission distribution in said oscillator.

5. An electron discharge device oscillator comprising a linear cathode, a plurality of spaced anode segments surrounding said cathode, the circumferential lengths of said anode segments being a multiple,- including unity, of a half wavelength long for a desired mode of oscillation, means for producing a constant magnetic eld having flux lines in a direction parallel to said cathode, whereby the electrons emitted from saidcathode circle the cathode in one direction, the circumferential portions of said anode segments defining inductances, the spaced portions of said anode segments forming capacitances in circuit with said inductances in virtue of which electrons impinge substantially solely on one edge of each anode segment to produce oscillations in a circumferential direction around the anode segments, said one edge of each anode segment being thicker than the other portions thereof to hasten heat dissipation.

6. An electron discharge device oscillator comprising linear electron emitting means, a selfcontained oscillatory circuit comprising a plurality of spaced arcuate anode segments surrounding said electron emitting means, said means comprising a plurality of coats of electron emission material of the same number as the number of anode segments, said coats being parallel and symmetrically arranged relative to one another in such manner as to prevent electron dispersion in undesired directions, the circumferential length of each of said anode segments being electrically a multiple, including unity, of one-half wavelength for a mode of oscillation, said circumferential portions defining inductances, the spaced portions of said anode segments forming capacitances in circuit with said inductances.

7. An electron discharge device magnetron oscillator comprising a linear cathode, a self-contained oscillatory circuit comprising a plurality of spaced anode segments surrounding said cathode, means for producing a constant magnetic field having flux lines in a direction parallel to said cathode, whereby the electrons emitted froml said cathode circle the cathode in one direction, the circumferential lengths of said anode segments being a multiple, including unity, of a half wave-length long for a desired mode of oscillation, and grid Wires of the same number as the number of said anode segments arranged parallel and symmetrically around said cathode for direction parallel to said electron emitting means,v

the circumferential portions of said anode ,seg-i ments dening inductances, the spaced portions of said anode segments forming capacitances in circuit with said inductances, and means for con- 8 trolling the electron emitting distribution in said oscillator to prevent"4v dispersion of electrons in undesired directions.

9. An oscillator in accordance with claim 7, in

cluding means for maintaining said anode segments at a positive potential and said grid wires at a negative potential relative to said cathode.

10. Electron discharge apparatus comprising a linear cathode, a self-contained oscillatory circuit comprising a plurality o1' spaced anode segments surrounding` said cathode, the circumferential lengths of said anode segments being a multiple, including unity, of a half wave-length long for a desired mode of oscillation and said circumferential portions dening inductances, the spaced portions of said anode segments forming capacitances in circuit with said inductances,.

CLARENCE W. HANSELL.

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