US2489156A

US2489156A - Oscillation generator of the reflex type

Info

Publication number: US2489156A
Application number: US478560A
Authority: US
Inventors: William W Rigrod
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1943-03-09
Filing date: 1943-03-09
Publication date: 1949-11-22
Anticipated expiration: 1966-11-22

Description

Nov. 22, 1949 w, w, RlGROD 2,489,156

OSCILLATION GENERATOR OF` THE REFLEX TYPE Filed March 9, 1943 13 Z5 INVENTOR BY ,umm

ATTOR NEY Patented Nov. 22, 1949 OSCILLATION GENERAP'IOR OF THE REFLEX William W. Rigrod, Bloomfield, N. J., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 9, 1943, Serial N0. 478,560

7 Claims. (Cl. 315-5) This invention relates to velocity-modulated generators and reflector electrodes for electricity of ultra-high frequency. and more particularly to a special construction of reflector electrodes to facilitate the focusing of electron beams.

The primary object of my invention, generally considered, is to provide an improved means for adjusting the transit time and controlling the focusing of electron beams, especially in velocitymodulated generators for electricity of ultra-high frequency, of the type generally designated as reflex Klystrons.

Another object of my invention is to provide an improved velocity-modulated tube, and especiall,1 one of the reflex Klystron type, whereby the electron transit time and the focusing of the electron beam may be more readily controlled.

A further object of my invention is to provide means in a reliex Klystron for focusing the returned electron beam by merely controlling the potential of an inner element or cylinder disposed between a reflector electrode and a resonant-cavity member.

A still further object of my invention is to provide an improved reflex Klystron in which the electron beam may be controlled without changing the voltage of the reflector electrode.

Other objects and advantages -of the invention, relating to the particular arrangement and construction of the various parts, will become apparent as the description proceeds.

Referring to the drawing illustrating the invention:

Fig. 1 is a fragmentary axial sectional view of a device, of the type generally designated as a reflex Klystron, for generating electricity of ultra-high frequency.

Fig. 2 is a transverse sectional view on the line II-II of Fig. 1, in the direction of the arrows.

Fig. 3 is a fragmentary axial sectional view of a modified reflector electrode, associated focusing member, and part of the associated resonant cavity member, as shown in Fig. 1.

Figs. 4 and 5 are views corresponding to Fig. 3, but showing modifications.

Fig. 6 is a View corresponding to Fig. 3, but showing a modification in which the focusing element between the reflector electrode and resonant cavity member is dispensed with, the shape of the reflector alone being relied on for accomplishing the desired purpose.

In the reilex Klystron, electrons in the form of a beam, after being hunched by passing axially through an electric eld Oscillating at ultra-high frequency, enter a region of electric field, which retards them until they come to rest and reverse their direction of motion. During this round trip, the differential accelerations and retardations superimposed on their motions in the punching process, results in the formation of electron packets which, after reflection, retraverse the ultra-high frequency eld at times when that field most strongly opposes their motion. By suffering deceleration under the action of this eld, the electron packets or bunches give up energy thereto and so sustain its oscillations.

In order to convert the greatest fraction of the electrons kinetic energy into oscillating electric field energy, the direct retarding field, which effects reversal of the electrons direction, must be designed to:

(1) Focus the returning electron beam into the region of strongest oscillating field, and

(2) Retard the electrons at the proper rate so that the bunches are in the optimum phase relation with respect to said field.

In prior forms of the Klystron, a single reflector electrode has been used to perform both of the above functions, by varying the voltage (Es) of the resonant cavity member, cavity resonator, or shell and the reflector voltage (Er). The electrode design problem has thus been twice as diflicult as it would be were a separate electrode used to perform each of these functions.

In accordance with my invention, I propose to use a compound or specially designed reflector electrode, which desirably includes, in addition to the reflector member, one disposed between it and the resonant cavity member or adjacent grid, whereby the potential (Ez) of this member may be varied independently, as compared with that (Er) of the reflector. By applying such a device to a velocity-modulated beam-type generator for electricity of ultra-high frequency, such as a reflex Klystron, for example, desired results are obtained as follows.

An advantage of using such a compound reflector lies, not only in its superior versatility as 3 compared with a single electrode, but principally and specifically in its ability to control the focusing of the returned electron beam and its transit time, that is, its relative phasing as compared with radio-frequency voltage, independent of 5 each other.

If the potential of the shell or resonant cavity member is regarded as 100 and that of the reflector as 0, then it has been found experimentally that radio frequency power output was obtained from a reflex Klystron, equipped with a compounds reflector.U embodying.v my invention; when the .zpotential "ofathe associated' member; such as an inner cylinder disposed between the one or more leads or supports 35 for electrode means, such as an associated control electrode 36, here shown as hollow cylindrical, which with associated insulating material 3l between it and a generally cylindrical rim portion of said electrode 34, form a compound reflector device or electrode embodying my invention. The insulating material 31 divides the compound reflector electrode into a plurality of insulated zones, the spherical portion of the electrode 34, or second zone, being arcuate about the aXis of the opening in the surfaeeeofnther electrode S31-:considered as. the first zonen As `sthesdi'ameterf.ofthe opening" in the control electrode 35 is less than that of the elecreflector and shell, lay in the range between 0 andlsstmde 34, the surface of the compound reflector 19. The equipotential surface at which electrons reached zero velocity before :starting back in theopposite direction was in the range between `V and 35, that is, always positive with respect to the associated member or cylinder:

Thus, the turn-about positions forfthenelectrons end-plate or grid, showing that focusingzof--the electrode, subtends about a point in its central region,V asolidiangle substantially greater than Z'ir solid radians.

Whensin operation," a beam of electrons from zthesproperlyroriented cathode I2 passes successiveiywthrough i the f openings, intermediate the electronebeam-.projecting means I2 and the reiiector electrode, le'ft by the grids I'I, IB and 23, and-Histurned back, before reaching the reector returned beam depends entirely on the potential 34, at the equipotential `surface in accordance of saidcont-roLmember relative yto the. shellpotenel` tial.

Itwasfound-that best results couldbe obtained, forvjav. given: reiiector .-,potentiaL .when theinnerf tial. positive with. respect to thereflector cup for.-

allnvalfues.0f..shell.voltage.. This Ais an important?.l practical advantagenfonmy compound reflector-,-,

asfor any singlernode of operation the compound/.I

refiector:x requires: nos more adjustment than a .35t..}tentia1 singleelectrode.

Referring L-now .toy` thel drawingsr VinV detail, like e partssbeing g designated. .by =like reference l charaoters, andorst considering the embodimentof..

myinvention illustratedin Figsfl and12, there fis. y

shownuahportion..offa reflex'llystron II com@ prisingfan. electronfemissive cathode 4I2 supported" inside of an envelope portion I3, only-fragmen.- tani'ly ,1 illustratedl Said envelope `portionhas sa collanfor outstanding-.;annular angemember I4--45V52 extending, from .its..periphery,. and at.-.one endo partly closedby grid-support member I5 having,-

a collar I6 providing an opening furthe passageff of.electrons...and..toewhich `grids. I'I eandvrl :are secured.

n) Thaupper portion', of the collar `-I 6 -denes ythe interior portion .ofVA the.- .cavity `resonator orshell: member I 9, secured r`thereto #by 4means-fof? atflexe, ible. diaphragm. or..lo.wer-wall portion: 2|.. The

remainderpf Ithe resonator `member .consists of..v 1

in.. fthe present embodiment,,projects a coaXiaL- I output memberor antenna. 255.F Mechanical ktun.-l ing. or ,adjustmentof .the resonant cavity. `may Ybe eected .by turningaplurality of screws 26.to flex..

theamember: 2.Ldto.ai greater `orlesser extents.

{35.trolledf in any desired manner; as from' the-sameH against. .theyresistaneeof the-tension coil springs.

21,; acting, betweenthe flange. member.. I4 and .aM

correspondingflange ,member 2.\to whichv the upper. wallportion. 22:.andthe cylindrical...wall

portion24arewseeured, asibymeansxof solder 29..

Projecting axially firomi the flange .f member..28..f70 L;

is .:a..sleev.e..member 3I-,closed atv itswouter: or upper,endbya.flare member 32,4 yof glass or... other vitreous material, through: a press .--,of Whichnpass .af-rod or` support. 33k for areector withsthevelocity;-thereof.v The equipotential surfaces:arefnot'shetched in Fig;l l, but correspond-1n inglsurta`ees-f38fand '39 are-,shown in Fig. 6.- Anf electron :having -a relatively slow velocity may be@ or `control:member waskept at. alconstantpoten- A30V.re-lectedfatfa relatively. high potentiar surface-1.

corresponding; for example, with the-one-desi'gnatediasx,Whilefarelatively fast Lelectron may penetrate'fsuch:surface fand nally be reflected-at.'y

a ysurtac'e such i as -3 9 Vhaving a more negative' po`v reflect all of the electrons back into the shell-orv resonaton'device and. avoid undesired Vdispersion thereof.

Fig'al .alsoillustrates'a wiring ,diagram which Inany -event-,.however, the yreflector sur`^ face willlxbefconcaveyor'of such acharacteras to.,V`

mayrbe usedfrinl the. operation offlthe generator.

The i-cathodefi 2,." forexample, may be heated by".

energy'ffrcm; an] adjustable transformer `l I `the primar-y: winding-"5421off-whichfis'connected to a suitable'esource-ofripower and the secondary windingfllsoffwhichds connected to-the heating` The shell or res-- lament. IIIIIy :of: fthe -cathode.- onant cavity member I9, desirably groundedas.

tialnbeingfindicated bythe` movable arrow 46.

ode.;I2,-;.asnbymeansfof abattery 4l or other V'Ikhefreector-member.3s is maintained at a negiative potentialrxEr) witnrespeet to thel shell member I9, as wellas withzrespecttothe cathsource of direct current, adjustability being. in-

`ydicatedtby.theumovable arrow 48.. The1potenftial of the .control element 33., in-this. case shown hollowe'cylindnical, `andat a potential positive` with respect to the reflector lkrandlintermediate that: ofsaidreflectorfand the resonator I9, is conbattery-"IIIeby means of the movable -or adjustable meansor connecting member 49.l The cathode shield 53 is..maintainedat. a .relatively small positive potential with respecttothe. cathode. I2,.by.

lbatteryorl other .source of direct current. 54.

If' the eleetrode`f34'ffhere rshown; generally spherical, andinaapotentiaMEzh` oi.- the-,.cylindrcal` control member- 3B is kept constant, however, the field lines near its mouth will be essentially unchanged.

Thus I have found experimentally that with the potential difference between the reflector member 34 and the cylindrical member 36 fixed at any one of a number of optimum values, the reflector potential (Er) for any one of a number of modes in each case remained essentially constant for best output, as the shell voltage (Es) varied over a wide range. This potential difference, Eb=ErEa Thus for each value of the inner cylinder voltage (Ez), the compound reiiector of the shape depicted in Figs. 1 and 2 can be regarded as a single deep concave reiiector, of a correspondingly adjusted depth, while having the same mouth diameter and general shape.

The following table shows typical operating data for a reflex Klystren with a compound reector, as in Figs. 1 and 2.

R t PositiveI Volt- R F e ec or age on nner Shue gom Cup Po- Cylinder Relg tential E, ative to Rewatts) Hector Cup El,

Another desirable configuration for a compound reiiector, corresponding generally with that shown in Fig. 1, is illustrated in Fig. 3, in which the reflector member proper is designated 34*l while the focusing or control member is designated as 3Z-y ,the adjacent grid of the resonant cavity member 19a being designated as 23a. The members 34gq and 362L may be held together by suitable insulation (not shown), as in Fig. l. In the present instance the reflector member 3Aa is not only shaped somewhat differently, but the control member 36E is hollow frusto-conical rather than cylindrical.

Referring now to the embodiment of my invention illustrated in Fig. 4, the reflector member is here designated by the reference character Sb, while the associated control member is designated as 36h, the grid of the associated resonant cavity member lb being designated as 23h. In this case, the reflector member is like a hollow cylinder of short axial length and closed at only one end, while the control member 36b is like a surface of revolution, somewhat frusto-conical except that it curves longitudinally as well as circumferentially.

The embodiment of my invention illustrated in Fig. involves a reiiector member 34C, somewhat like the reiiector 34EL of Fig. 3, and a control electrode 36C in the form of a fiat plate with an opening 5l of a diameter less than that of the mouth of the reflector member 34c but, like the corresponding openings of the other forms, at least as large as the adjacent resonator opening or grid. The associated resonator is designated by the reference character |90, the adjacent grid thereof being 23.

In designing single electrode reflectors for reflex Klystrons, the chief consideration has been to obtain the maximum power conversion effl- 6 l ciency in producing radio-frequency oscillations. The result has been, in most commercial models, a shallow cylindrical cup, whose base is given a slightly concave curvature facing the cathode.

In some Klystrons the radio-frequency power output tends to decrease sharply with slight deviations of the shell or beam-accelerating voltage (ES) from its optimum value. However, a fairly broad range of shell voltage can be used without sharp decline in power output, providing the reflector voltage (Er) is readjusted at each successive change in shell voltage. This adjustment of reiiector potential to get maximum power output, for any value of shell voltage, is fairly critical.

It is clearly an improvement, increasing ease of operation and maintenance, if a reflector is used so that one of the two voltages (Es and Er) can be varied over a wide range without greatly affecting the radio-frequency power output of the oscillator. Anembodiment of such a reflector is illustrated in Fig. 6 and designated by the reference character 34d. When using such a reflector in a Klystron, as illustrated in Fig. 1, the shell potential may be varied over a range of more than 500 volts with a constant reflector voltage (Er) with sustained maximum radio-frequency power output.

'Ihis means that, in addition to maintaining good electron-beam focusing .over this range of (Es), the reflector configuration also gave rise to approxi-mately constant transit time for the corresponding range of penetration distances of electrons into the reiiector region, @with unchanged voltage Iapplied to the reflector.

The essential features of my reflector, illrustrated in Fig. 6 are:

(l) Cylindrical rim :portion close to the outer surface of the adjacent Wall of the resonator member (ld) producing an equipotential field contour of high curvature, as shown lby the dotted lines designated 38 and 39, and in terms of electron optics, short focal length.

(2) The `depth of the remaining or generally spherical portion of the reflector cup 34d is shown approximately as great as the radius of its mouth. The bottom need not be spherical, as illustrated, but can be flat or otherwise formed, its shape having little effect on the equipotential surfaces lat which the electrons come to rest and reverse directions, as these surfaces are close to the mouth of the cup, due to the high iield concentration there. The depth of the cup is necessary to permit these equipotential surfaces to assume vthe desired shapes, such that electrons penetrating to desired distances are returned in a beam focused t0 approximately the same position on the tube axis between the cavity grids.

Another way of regarding this operation is to consider the reflecting equipotential surface as lan electron-optical mirror. Inasmuch as any transverse force acting lon an yelectr-on changes its direction .of motion most greatly when the electrons velocity is least, the electrostatic forces :acting on the electrons when they come to rest are most important in determining their return zpath. Thus the equipotential surfaces in the neighborhood of the turn-about position must have focal lengths which are roughly 'proportional to their distances from the region .between the two cavity grids, in order that electrons of a large range `of entrance velocities will .be returned and refoc-used vat that position. This is shape illustrated in Fig. 6.

In general, variations of the shell voltage changes the qualltyof `the radio-frequency output-by altering both` its magnitude land its irequency. In the-former design of Klystron, any changein the shell voltage must be accompanied by a-corresponding' change inthe reflector volt'- afge tofmaintain :approximately constant transit time and so sustainoscillations. By using either the single orfcompound reflector embodying my invention, both of' these variations in output may be ei'ectedby changing only one voltage, namely, that' of the shell. For example, increasing the shell voltage', increases the frequency, and vice versa.

From the foregoingfit-will be seen that I have deviseda reflector'device,v which may :take either theforin iota compoundlor plural voltage refleet-or, or that-of la' single deep reflector, to 1facilita't'e the vadjustment of the transit time and control the "focusing of the electron beam in ,a generator of ultra-high Ifreq-uency. The control of amplitude `andfrequency may be effected by merely varying the shell voltage, once the potentials=of the electrodeelements have been pre-set for a` desiredrangeof' operation. In accordance with myV invention .the precision and flexibility in pre-settingthedesired mode of operation may be vastly increased'by using` a plurality of reflector elements-held.. at different potentials in place of ione, -to--perform individually the `two distinct :functionsfpreviously required of :the one.

Although :preferredembodiments of my invention` haver been disclosed, it will be understood that'modications imay kvbe `made within the spiritv and scope oftheappended claims.

l. A velocity-modulated high-frequency generator of theireex type comprising an electronemissive cathode, a cavityv resonator adjacent thereto, a reflector electrode toward which the output of said-cathode is directedl and disposed onfthe side offsaid'resonator opposite from that of said cathode, Aelectrode means disposed intermediate said 4reflector electrode and resonator, means vincluding asource-of voltage and conductors connected between -saidlsource f and vsaid resonator, said--reilector electrode, and said electrode means, for maintaining said resonator at a high positive :potential with respect to said cathode, said reilectorelectrode at a negative potentialwwith respect to saiducathode, and said electrodermeansatI a potential intermediate that of theresonatorand said reilector'electrode, in order. tocontrol thefocusing ofthe electron beam returned bysaidreflector electrode.

A2. A ,reex-Klystron comprising an electron-- emissive...cathode,.a A'cavity resonator associated therewith, a reflector. electrode disposed on one side ofcsaidresonator opposite that of said cathode said .electrode `'having a, reflecting surface shapedgenerally like' a portionA of asphere open- 81 ing axially ofthe 'Klystron, a cylindrical rim portion disposed coaxially therewith, partially closing the mouth thereof, and extending therefrom close to said resonator, for producing an electric eld contour of high curvature, lead-in means from said cathode, resonator, rellector electrode, andl cylindrical riml portion, and sources of potential connected to said lead-in means for maintaining said cylindrical rim portion positive with respect to said reflector electrode, but still negative with respect to said resonator, in order to control the focusing of the electron-beam returned by said reflector electrode.

3. In an oscillation generator of the reflex type, a cavity resonator' having an opening in each of opposite Iwalls, means for projecting a beam of electrons through said openings, a reilector electrode disposed on the side of said resonator opposite Ito that of said projecting means, formed with a concave generally spherical surface adjacent said resonator and aligned with the openings, and an electrode member, formed hollow for the passage of the electron beam, partially fenclosed in said reflector electrode, disposed ;coaxially of said generator, positioned betweeniand insulated from said reilector electrode and resonator, and having an opening adjacent said resonator at least as large as the adjacent resonator opening. A

4. A cavity resonator having a pair of openings in its Walls, means for projecting a beam of electrons through said openings and a reector electrode aligned `with said openings and comprising a hollow member having conducting wall portions subdivided into a plurality of insulated zones, said openings being intermediate the means and the reflector electrode,and adjustable means connected to said zones for varying at will independently for each of the zones the relative electrical potentials of said zones and said resonator.

5. A reflector electrode for an oscillation generator of the reflex type comprising a hollow body having a surface of conducting material subdivided into a plurality of Zones insulated from each other, and having an opening in the surface of a first one of said zones, a second one of the zones having an inner surface arcuate about the axis of said opening.

6. A cavity resonator having a pair of openings in its Walls, means for projecting a beam of electrons through said openings and a reflector electrode aligned with said openings and comprising a hollow member having conducting wall portions subdivided into a plurality of insulated Zones, said means being oriented relative to the openings and the electrode to project said beam through the openings toward the reflector electrode, and adjustable means connected to said zones for varying at Will the relative electrical potentials of said zones and said resonator, the surface of said reilector electrode subtending, about a point in the central region of said reflector electrode, a solid angle substantially cgreater than 21r solid radians,

7. In an oscillation generator of the reflex type, a cavity resonator having aligned openings, means for projecting a beam of electrons through said openings, a reilector electrode disposed on Ithe -side of said resonator opposite to that of said vprojecting means,aligned with the openings, and presenting to said resonator a cup-shaped surface, andan electrode member, Ainsulated from, and partially bridging the gap between, said reflector electrode and resonator, formed with an WILLIAM W. RIGROD.

REFERENCES crrnn The following references are of record in the 111e of this patent:

UNITED STATES PATENTS Number Name Date Henneberz et al. June 27, 1939 Number Name Date Cage Feb. 13, 1940 Varian v.. June 17, 1941 Varian et al. July 29, 1941 Hansen et al. Oct. 21, 1941 Linder Mar. 17, 1942 Morton Mar. 31, 1942 Linder Aug. 18, 1942 Harrison et a1 Jan. 21, 1947 Hill Mar. 18, 1947