US2578699A

US2578699A - Cavity resonator electron discharge apparatus

Info

Publication number: US2578699A
Application number: US777801A
Authority: US
Inventors: William W Hansen; Russell H Varian
Original assignee: Leland Stanford Junior University
Current assignee: Leland Stanford Junior University
Priority date: 1939-08-24
Filing date: 1947-10-03
Publication date: 1951-12-18
Anticipated expiration: 1968-12-18
Also published as: US2460288A; GB545779A; US2683775A; FR882595A; NL80761C

Description

w. w. HANSEN x-:TAL 2,578,699

CAVITY RESONATOR ELECTRON DISCHARGE APPARATUS Original Filed Aug. 24, 19'39 l az l @hqhmil lgi//M L 7# TTORNEY Patented Dec. 18, 1951 CAVITY RESONATOR LECTRON DISCHARGE APPARATUS William W. Hansen and Russell H. VarianStan ford University, Calif., assignors to The Board of Trustees of The Leland Stanford Junior University, Stanford University, Calif., a legal entity of California Application December 6, 1943, Serial No. 513,002, which is a division of application Serial No. 291,652, August 24, 1939. Divided and this application October 3, 1947, Serial No. 777,801

This invention relates to hollow cavity resonator electron discharge apparatus and is particularly concerned with structural and 'circuit improvements in such apparatus.

This is a division of our Patent No. 2,460,288 for Resonator Apparatus, iiled December 6, 1943, as a division of application Serial No. 291,652, filed August 24, 1939, for Dielectric Guide Signaling, now Patent No. 2,375,223.

It is a major object of the invention to provide i hollow cavity resonator electron discharge apparatus having adjustable energy coupling arrangements.

A further object of the invention is to provide novel hollow cavity resonator electron discharge apparatus wherein a suitable member is shiftably mounted in the electromagnetic eld of a hollow resonator device having an evacuatedsection through which an electron beam is passed in such fashion that coupling of said member with the eld may be controllabl'y varied from outside the device without disturbing the vacuum seal.

A further object of the invention is to provide hollow cavity resonator electron discharge apparatus wherein a `shiftable conductive, member terminating a high frequency transmission line extends within a hollow resonator for variable coupling with the high frequency field within said resonator, that part of the resonator eld with which said member is coupled being sealed off from the remainder of the resonator interior by vitreous or like wave-energy-permeable wall means permitting said coupling. Speciiically the coupling member may be rotatable for changing the amount of energy transfer between the transmission line and said eld.

It is a further object of the invention to provide hollow resonator apparatus wherein an evacuated hollow resonator device is connected in a novel mannerto an electromagnetic wave energy conducting means through use of a vitreous seal.

Further objects of the invention will presently appear as the 4description proceeds in connection with the appended claims and the annexed drawings, wherein:

Figure 1 is a side elevation partly diagrammatic and partly in section of hollow cavity resonator electron discharge apparatus embodying the in- Vention as used for amplifying signals projected along a dielectric wave guide; and

Figure 2 is a side elevation of a further embodiment of 'the invention wherein Wave .guide r15l claims. (allais- 39) Cil sections are directly coupled to the resonators of an amplier.

The term hollow as used herein in describing resonators and dielectric or hollow-pipe wave guides is of course intended to embrace all such resonators and dielectric or hollow-pipe wave guides regardless `of whether the dielectric therein is air or some other medium.

Fig. 1 illustrates relaying apparatus including a hollow resonator device I I for picking up a signal traversing a wave guide I2 from left to right, amplifying the signal and then reradiating the same for continued transmission along the wave guide. This'relaying apparatus includes directional discriminating means for receiving the signal to be relayed and for reradiating the signal after it has been amplified. The relaying apparatus is not responsive to signals coming from a direction lopposite to its direction of sensitivity and hence will not cause interference with .signals traversing the guide in that opposite direction. Ordinarily a similar relaying device with opposite directional characteristics is ernployed in the wave guide for relaying signals in the opposite direction, as described and claimed in said Patent No. 2,375,223.

Spac'ed signal receiving meansi and lL'which may be of any suitable type such as the illustrated dipole antennae, are suitably located in wave guide I2. A phase shifter designated at I5 is supplied from antenna i3, while an amplitude adjuster designated at I6 is supplied from 'antenna I4. The outputs of the phase shifter and amplitude adjuster are combined as illustrated in hollow resonator device Il which is an ultrahigh-frequency amplifier. The output of ampliiler I I is supplied through a second phase shifter Il and amplitude adjuster I8 to reradiating antennae I9 and 2|.

Phase shifter i5, connected to receiving' antenna I3, is illustrated as a concentric transmission line which is adjustable as to length. A concentric line portion 22 which is shiftable axially of wave guide I2 extends through an opening 23 provided in wave guide I2 and has dipole i3 connected with its upper end. The lower end of concentric line portion 22 is provided with a female socket for telescopingly receiving the upper end of a relatively iixed concentric line portion 24. A screw 25 having a knob 26 is threaded into a bracket 2l fixed on wave guide- I I. Screw 25 is rotatably mounted on a lug 28 integral with line portion 22, and is otherwise so connected With lug 28 that rotation of knob 26 varies the axial distance between dipoles I3 and i4, therebyvr varying the phase difference between these dipoles within the wave guide. The concentric line connecting dipole I3 to amplier II is thereby changed in length so that rapid changes in phase of the outputs of the two dipoles as supplied to the amplifier may be effected by adjusting phase shifter I5.

Concentric line portion 24 terminates in a conductive loop 3| which isx coupled to deliver energy to amplifier I I as will be described.

Amplitude adjuster I6 comprises an upper concentric line portion 32 connected to receiving antenna I4 after extending through a suitable aperture in wave guide I2. The lower end of line portion 32 is formed as a female socket which is rotatably connected with the mated upper end of a short concentric line portion 33 having a manual operating knob 34. At its lower end concentric line portion 33 terminates in a conductive loop 35 which is coupled to deliver energy to amplifier I I as will be described.V Thus loop 35 is rotatably mounted with respectl to the concentric line between antenna I4 and amplier II.

Amplifier II preferably is generally of the cascade type disclosed in United States Letters Patent No. 2,280,824, issued April 28, 1942. Amplier II comprises a plurality of aligned interconnected dielectric or

cavity resonators

36, 31

and 38 which are evacuated. Within a vitreous insulating cup 39 at one end of the amplifier is provided a cathode 48 surrounded by a focusing shield 4I, said cathode being indirectly heated by a heater coil 42 that is supplied from the battery 43. The electrons released by the cathode 40 are drawn in a columnar stream by a strongly positive grid 44, which-grid is held positive with respect to the cathode by a battery 45. Note that the positive side of the battery 45 is grounded, which is also true of the casing of amplifier II, to which casing grid 44 is connected. The electron stream drawn through grid 44 passes through subsequent pairs of

grids

46, 41, 48, 49, and I, 52, constituting grids of

hollow resonators

36, 31 and 38, respectively. After leaving grid 52, the electron stream passes through additional inclined

parallel grids

53 and 54 to a collector and detector plate 55.

Loops 3| and 35 are both disposed within input resonator 36, so as to 'be coupled in energy exchanging relation with the electromagnetic field of the resonator as will be described. A suitable vacuum tight sealed joint employing a body of vitreous material as indicated at 56 is provided Where concentric line portion 24 is joined to resonator 36.

A partition 51 of vitreous material is provided within resonator 36 so as to seal off that section of resonator 36 within which rotatable loop 35 is disposed from the remainder of the resonator interior. Partition 51 is of course made of a material which is permeable to the resonator field and permits the resonator field to couple with loop 35. As illustrated, partition 51 provides an outwardly facing pocket accommodating loop 35.

Resonator 38 is also provided with a frequency control device indicated at 58 comprising a glass or like vitreous pocket or envelope 59, the closed end of which extends well into the interior of resonator 36. 'Ihe open outer end of pocket 59 is sealed off along the edge of a suitable aperture in resonator 36, as illustrated, so as to be vacuum-tight. A metal plug 6I is suitably mounted for longitudinal advance or retraction 4 within pocket 59, as by rotation of nut 62. Similar

frequency control devices

63 and 64 are provided on

resonators

31 and 38, respectively.

Within output resonator 38, conductive loop 65 is disposed in a section of the resonator which is sealed off from the remainder of the resonator interior by a vitreous partition 66 similar to partition 51. Loop 65, like loop 35, is rotatable for variable coupling with the associated resonator field. Manual knob 61 of amplitude adjuster I8, which is structurally the same as amplitude adjuster I6, is provided for selective rotation of loop 65. Loop 65 is thus connected to transmitting antenna 2| in the same manner that loop is connected to receiving antenna In like manner conductive loop 68 within resonator 38 is connected to transmitting antenna I9 through phase adjuster I1 which is identical in construction and operation to phase adjuster I5.

Thus in each of

resonators

36 and 38, the electrically conductive inner surfaces of the resonators substantially define envelopes bounding the electromagnetic fields. The conductive loops and shiftable frequency control elements are all at least in part disposed within the physical confines of those envelopes, for coaction with the fields. The rotatable coupling loops are disposed in non-evacuated sections of the envelopes.

As illustrated loops 35 and 65 may be inserted into or withdrawn from their associated resonators without impairing the vacuum seal of the resonators.

During operation, the indicated wave energy traveling along wave guide I2 from left to right is picked up by receiving means I3 and I4 and delivered to resonator 36 in in-phase relation.v

'Ihis received energy serves to excite resonator 36 in such mode that an alternating current electric field is established within resonator 36 and between

grids

46 and 41, the said electric eld serving to alternately impart positive and negative accelerations to successive electrons of the stream passing therebetween; thereby causing the electrons of the stream to traverse the space between resonator 36 and the next resonator 31 with cyclically varying velocities. The faster electrons which passed through the electric eld later than the preceding electrons will tend to overtake the latter in the interspace between resonator 36 and resonator 31, so that by the time the electron stream has arrived at grid 48, the stream will have a slight periodic variation in electron density at the frequency of the field between

grids

46 and 41.

' If intermediate resonator 31 is properly tuned, which is accomplished by tuning means 63, an alternating electric eld will be established between grids 48 and 49, which is much stronger than that existing between

grids

46 and 41, with the result that the successive electrons will receive much larger variations in velocity than that previously possessed, thereby effecting still greater bunching and corresponding increase in variation in electron density during passage through the space between

resonators

31 and 38. Similarly, the entrance of the stream of variable electron density into resonator 38 establishes a strong alternating electric field between grids 5I and 52 which acts to retard the electrons so that they do work upon this field and thereby maintain the alternating electromagnetic field within resonator 38 and energy from the field is picked up by loops 68 and 65 and reradiated novatonlong Awave guide H12 :by itransinitting mreans H59 iandzt; n

Grid 53, being at the potential of .the .:positive .sidef.ofibattery:,45, aidsinimaintaininguthefstream in :coimnnar iform, whereas :inclined sgrid rfid .is preferably maintained at 1a .potential mear ethat o'f .the cathode 'ilhis accomplished-:by luseroi potentiometer ffii) :and battery ill :connected sto cathode :lead .'12, Withxgridr'lrat this ipotential, 4most-.of the .electrons -:are rreflected '-back rand Pto one side, and only the speededeupelectrons will pass through this grid. Thusfas theychangein ,electron Nelocityincreases, morefanrii-more iof the 'faster ielectrons will :reach plate .55 beyond .grid 54, while fevver of the slower `electrons will rreach :this `fplate. `the *current therefore :reaching ,plate 55 `increases .as the amplitude of joscillations .in .the hollow resonator device increases, iso that said `dev-ice asa whole serves-.as a .cascade ,ampli- 'fler1and..detector. d

YIhe 4detected signal on the -plate -55 isfinore .negative the .strong-er .fthe-oscillations rbecome. Looked atinano'ther way.as.thevcurrentthrough the :plate circuit increases, 1.tl-iedrop,across .a re- .sistor ".I3 .in .the .plate .circuit increases, thereby i lowering the potential .at plateZ `whirinis shown connected through-.5a lbias'ing :battery .it and lead .75 .toa grid .1E ,positioned fin rfront -of emitter 4I). Thus the .potential .of rgrid 'IB lis correspondinglylowered, .effecting .a .decrease in the current passing .through the device flue to the repellent .action of vthe grid ll on the .electron stream. Thus, since plate 55 becomes .more .neg- Vati-ve .as the signal Iintens'ity increases, grid It `acts as :an automatic volume control serving -to m.

As above described, the tuning devices 'sup` plied 'to each 'resonator consist of vitreous en.- velopes 59 that Vextend .into 'the resonators -and ,prevent .theiadm'ission of 'airth'ereinto I `The `-posi- 'tion in which the envelopes 'T59 andthe associated metal Aplugs project 'into Vthe resonators has an I'important bearing on `the tuning.. If the Vmetal plug is 'positioned in Va .part of the resonant cavity containing 'essentially 'electric field, 'the Y.1o-lug serves to increase the capacity of the 'cir' 't'.so that the resonant :frequency will be decreased; whereas if this plug is inserted in .a're'gion containing mostly magnetic held, it reduces the total volume of magnetic 4field .since 'theplug contains no iield, whereby Jvthe inductance will be de; creased 4and the Vfrequency will be increased fit is therefore possible toiind an'interrnediate point where the mere presence of the 'plug will .not :affect the frequency. `As illustrated 'in Figure l, fthe metal plugs are located where the magnetic field 'is strong. As the plugs are moved in' and 'out, controlled changes "in the `resonantfrequency of the resonators is obtained, there'byallowing vthe various resonant Achambers '36 `to v3B to' be ftuned to the incoming signal.

Rotation of loop 35 by 'manipulation *of knob 134 alters Athe number of magnetic lines "oi" 'altere mating current flux .resonant 'inhollow'resonator 33 'that 'are enclosed by 'the loop, thereby varying the intensity of the signal that is-`set up in resonator 36 .byagiven signal passing'along Ware guide `I2 fromfleft to right. Similarly, rotation -of loop 155 by .rotation of `knob 6'! 4varies -the 'intens'ity of the amplified signal dfelivered to waive guide I2.

Thus energy traveling from left tofri'ght along waveguide I2 islpickedupiby receiving antennae I3., Illfand deliveredto caseadeeniplifierf-H'. 'T-n'e 'amplfredisignal is in 'tu1:narerauiated in theforigina-l direction alongivvaveaiguide .I 2 drum antennae I9, ZI. kv'Suitalo'le phase @and `:amplitude iadus-tments areprovided fat F'bcth the :input rand i output of fainpliiier .'Izimand 1 an automatic volume Vcontrol is providedjior varying -the :amplification tinversely to 'variations-in amplitude of the-received signal;

.Beceivingantennae I3 .and .M rare ,preferably located about -fone-quarter Wave length fanart withinwavefguide I.2,; that is, they rare :spaced a distance apart :such ythat fthe waves .received by antennae t3 and fI-tare :substantially 90 apart in `fphase 1due `to thetime l:consumed by the wave travel-ing this distance. .Phase shifter I5 :is adjusted ,by ti1rni-ngitsfcontrol .knob .25 so.=that the .electromagnetic .waves delivered vtherefrom to resonaton38-.are.phasewith the lwaves -delivered toresonator r36 `from the amplitude adjuster `I6 when `the received electromagnetic waves are 'traveling from-.left to right wave guide ,I`2.`..'Ihus, though .the antenna AIltis displaced yone-quarter 'wave .length from antenna I 3., the output of -amplitude adjuster '1I 6 is .phased with the "signal lreceived 'from the phase shifter E5.. 4`"Thus, "the 'outputs ojante'iin'ae `I3 and .I4 fare corfnbiiiedfadditively'for 'supplying ultranignffrequeney amplifier .11.

However, 'Should a .signal'be received by antennae. lll'and 1.3, coming "from the reverse direjction, "that'is, moving from 'right-to left in'Figuitel, 'then in that case .'the electromagnetic waves"received at "I3 will be 90 displaced "later tnanfthoseireceiveii at T4, and since phase vshifter I5 and 'theconnections shown .act to retard the phase "of the output of'a'ntenna I3 `-90 more, the output of the phasefsliifter yI5 will be directly out of. phase vwith 'that supplied resonator 3'16 from amplitude adjuster f6. .'llhus, lthese .reversely moving signalsw'ill tend to cancel each other. `If

the amplitude of 'these reversely moving signals is 'made identical by adjusting `the`knob 3iA of amplitude adjuster I6, Vthe effect of the signal com'in'gf'frornftheright atiamplier I `I will be zero duev to the.'canceiling of the opposite signals. Thus, "if receiving -means I3. and I4 .are -approxiinately 'one-quarter Wave length apart iin the guide, their 'combined vsensitivity .in one direction, e., ifor 'signalsjmovingfrom the left ltovvard lthe right, .will vbe substantially a maximum, whereas 'for signalsmovingin the opposite direction the conbined 'se sjiti'vityzwillbe zero. YIt is not esseri'tial that these receiver'means 'be exactly onequarter wave length apart, as some .departure ,from` thisvalue will not appreciably 'affect the sensitivity o'f fthe system. Since it is necessary 'that the Lsensitivity of the apparatus 'to signals traversing the guide in 'the reverse direction should be as 'near zero as possible, 'the receiving 'means are 'set up, 'inpractice as near one-quarter Wave length apart as convenient, or 'some bdd multiple thereof. The final elimination '0f the sen itivity ftofilow in `'the Wrong 4direction is ob- -tained byfiine'fadjustlnent 'of the phase shifter knob 26a-nd theja-'rnplitude Vadjuster knob 34.

"Phase shifter 4I *I 'acts to retard the Vphase ofthe Waves i"emitted ifrom antenna I 9 by 90 relative to thesphase of the wavesemitted from antenna 2 I.

`is :spaced along'vvave Vguide 'f2 about 'onev'cliaiter' wave 4length therefrom, so 'that by the time the waves yfrom'antenna 21 have reached antenna ISQ'tfhe' combined waves are in phase "for `(tra'n'sinfissi'on alongivavefg'uide I2 Ytciw'ard the right; 'Antennae "I9 Jand 2l, on theother hand,

75 aresub'traetive their action so iar as transmission to the left is concerned. ,Thus, radiation from antenna I9, upon reaching antenna 2|, will be displaced 90 from that which would be received at antenna 2| were phase shifter |1 not used, but since phase shifter I 1 retards the phase by 90 more, the net'result is to establish an 180 out-of-phase condition between the signal emitted at I9 and that received at 2| from I9, so that these two signals cancel out and hence do not traverse the wave guide toward the left, i. e., in the wrong direction. Further action of the relaying and associated apparatus in connection with ultra-high-frequency energy transmission is disclosed and claimed in Said Patent No. 2,375,223, to which reference is made for further detail. The present'invention is concerned mainly with above-described features relating to the amplifier and associated arrangements.

In Figure 2 an electron-beam-excited hollow resonator device 18 is directly connected between Wave guide sections 19 and 8| to relay and simultaneously amplify a signal passing from left to right along the wave guide.

Device 18 is here a two-resonator amplifler, embodying a hollow input resonator 82 similar to input resonator 36 and an output resonator 83 similar to`output resonator 38 in Figure 1. Resonator. 82 is provided with spaced grids 84, l85 and resonator 83 is provided ,with spaced grids 8B, .81.

Tuning devices

88 and 89, similar to that at 58, are provided for

resonators

82 and 83. As indicated by corresponding reference numerals, the various electrode and automatic volume control arrangements are the same in Figure 2 as in Figure 1. Device 18 has no intermediate cascade amplierresonator such as that at 31 of Figure 1 and hence operates similarly'to the usual tworesonator amplifier disclosed in United States Letters Patent No. 2,242,275. Hence amplifier 18 is similar to amplifier I I, except for details of coupling to the wave guide which will' be described below. l v

Output resonator 83 is formed with an energy output aperture |88 sealed by a glass or like wall |89. The adjacent end of wave guidesection 8| is slotted to permit passage of an apertured gate plate 9| having aperture 92 adapted to register with aperture 88. Thumb screw 93 opposing a spring 94 is adapted toadjust plate 9| vertically to thereby varythe portion of the area of aperture 92 that registers with aperture 88. Thus, by rotation of screw 93, the impedance of guide 8| may be matched with the internal impedance of amplifier 18.

A similar adjustable gate structure is provided between input wave guide section 19 and resonator 82, as indicated by the corresponding reference numerals, for matching the impedanceof guide section 19 to the input impedance of resonator 82. f

In operation, ,energy from wave guide section 19 is delivered directly to excite resonator 82 and `cause velocity modulation of the electron stream. Energy extracted from thel electron stream by resonator 83 is delivered directly to wave guide :section 8|. Proper impedance match for best operating conditions is attained by the adjustable gate structures, thereby insuring highly eflicient performance. Hence signal energy traveling from left to right in Figure 2 is relayed and amplied at 'I8 with a minimum of losses.

It,will be understood that although the wave guide described herein has been illustrated as being of the hollow-pipe lsingle conductor type.

other types of guide such as dielectric guides or other enclosed-field energy conducting systems may also be used. l

`Since many changes could be made in the above construction and many apparently Widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. High frequency apparatus comprising a hollow body providing a conductive envelope for enclosing an electromagnetic field, said body having an aperture in a wall thereof, a pocket vacuum-sealed to said body, said pocket having a closed inner end portion within saidenvelope and having an open end facing said aperture, and said pocket being permeable to said field, a movable terminal portion of a high frequency transmission line extending within said pocket and having a conductive portion disposed in part within said envelope for coaction with said field, and means accessible externally of said body for moving said terminal portion and varying said coaction with said field.

2. The high frequency apparatus defined vin claim 1, wherein said terminal portion comprises a conductive coupling loop which is rotatable for varying its coupling with said field.

3. The high frequency apparatus defined in claim l, wherein said terminal portion comprises a conductive coupling loop located within said body at a region Where the magnetic field is strong and the electric field is weak.

4. High frequency apparatus comprising a hollow resonator adapted to contain an electromagnetic fleld, a high frequency transmission line, means connecting said line to said resonator comprising a conductive energy transfer member rotatably connected to said line and extending within said field, means coupled to said member for rotating said member, and means permeable to said field sealing off that portion of said resonator in which Isaid member is disposed.

5. High frequency ,apparatus ,comprising a hollow resonator adapted to contain an electromagnetic eld, a relatively stationary concentric conductor transmission line section, a rotary concentric conductor transmission line section connected between-said resonator and said stationary line section, a conductive energy transfer loop rigidly securedon said rotary line section and coupled with said field, whereby rotation of said line section produces corresponding rotation of said loop, and a pocket permeable. to said eld for sealing 01T that portion of said resonator in which said loop is disposed. f

6. An electron discharge device comprising an evacuated hollow resonator adapted to contain an electromagnetic field, means in said device for passing a stream of electrons through said eld, a rotatable field coupling member having its inner end physically within said resonator connected to said resonator so as to be readily removable with the vacuum seal of the resonator retained unimpaired, and means coupled to said member for rotating said member for varying the coupling of said member with said field.

7. An electron discharge device comprising an evacuated hollow resonator adapted to contain an electromagnetic iield, means aligned with said resonator for passing a stream of electrons resonator with the inner end of said coupler within said resonator and movable with the vacuum seal of the resonator retained unimpaired, and means attached to said coupler for moving said coupler for varying its coupling with said field.

8. An electron discharge device comprising an evacuated hollow resonator adapted to contain an electromagnetic field, means disposed on one side of said resonator for passing a stream of electrons through said field, a rotatable coupler having a loop at its inner end positioned physically within the resonator so as to be coupled to said field, and means coupled to said loop for rotating said loop Within said resonator with the vacuum seal of the resonator retained unimpaired.

9. An electron discharge device comprising an evacuated hollow resonator adapted to contain an electromagnetic eld, a pocket formation vacuum-sealed with respect to the resonator body having a closed end projecting into the resonator and an outwardly directed open end, a rotatable coupler inserted in said pocket formation having its inner end physically within the resonator and movable and removable with the vacuum seal of said resonator retained unimpaired, means located exterior to said resonator for rotating said coupler, and means aligned With said resonator for passing an electron stream through said field.

10. High frequency apparatus comprising a concentric transmission line device having inner and outer conductors, a hollov.7 resonator adapted to enclose a magnetic eld, means adjustably coupling one end of said device to said resonator comprising a rotatable energy transfer loop connecting said conductors and disposed within the physical confines of said resonator, and means coupled to said loop for rotating said loop, so that rotation of said loop varies the coupling between said magnetic field and said device.

11. High frequency apparatus for connecting a high frequency energy device to a cavity resonator coupled with an electron beam, comprising means for vacuously sealing a section of said resonator traversed by said beam, a rotatable energy transfer loop connected to said device and located in a nonevacuated section of said reso-` 10 f movable conductive loop extending into said pocket structure through the open end thereof into coaction with said field, and means in said device for moving said loop for varying its coaction with said eld while retaining said vacuum seal of said resonator.

13. High frequency apparatus comprising an evacuated hollow resonator, an aperture in said resonator, means in said apparatus permeable to electromagnetic energy vacuum-sealing said aperture, means adjacent said resonator for conveying electromagnetic energy, an adjustable coupling element at said aperture for coupling electromagnetic energy between said resonator and said conveying means, and means accessible externally of said resonator for manually adjusting said coupling. k

14. High frequency apparatus comprising a cavity resonator, an aperture in said resonator, means in said apparatus permeable to electromagnetic energy sealing said aperture, means adjacent said aperture conveying electromagnetic energy, and an adjustable coupling element at said aperture for coupling said resonator to said conveying means.

15. High frequency apparatus comprising a source of electrons, means for velocity modulating electrons emanating from said source resulting in grouping said electrons, means for extracting electromagnetic energy from said grouped electrons, said velocity-modulating means and said energy-extracting means including a cavity resonator, said resonator having an aperture, an electromagnetic wave energy conducting means having an aperture, the aperture of said resonator registering with the aperture of said conducting means, and a vitreous vacuum seal positioned in the vicinity of one end of said conducting means, said seal being permeable to electromagnetic energy.

W'ILLIAM W. HANSEN.

RUSSELL H. VARIAN.

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

UNITED STATES PATENTS Number Name Date 2,106,771 Southworth Feb. 1, 1938 2,153,728 Southworth Apr. 11, 1939 2,190,668 Llewellyn Feb. 20, 1940 8,200,023 Dallenbach May 7, 1940 2,222,902 `Hahn Nov. 26, 1940 2,237,878 Haef Apr. 8, 1941 2,259,690 Hansen et al Oct. 21, 1941 2,287,845 Varian et al. June 3, 1942