US2414496A - High-frequency tube structure - Google Patents

Description

Jan. 21, 1947.

S. F. VARIANj ETAL HIGH FREQUENCY TUBE STRUCTURE Filed March 24, 1942 3 Sheets-Sheet 1 FIG.I

ur Z i-iig 35E-lll Wall! .n

Jan. 21 1947. s. F. vARlAN Erm. Y 2,414,496

I HIGH FREQUENCY TUBE STRUCTURE Filed March 24, 1942 FIG. 7

5 Sheets-Sheet 2 Jan. 21, 1947. s. F. VARIAN Erm.

HIGH FREQUENCY TUBE STRUCTURE 3 Sheets-Sheet 3 Filed March 24,` 1942 FIG. IO

ArfoRNEY Patented Jan. 2l, 1947 HIGH-FREQUENCY TUBE STRUCTURE Sigurd F. Varian, West Hempstead, and Donald R. Hamilton, Garden City, N. Y., assignors to Sperry Gyroscope Company, Inc.,

Brooklyn,

N. Y., a corporation of New York Application March 24, 1942, Serial No. 435,954

'I'his invention relates, generally, to ultra high frequency tube structures and, more specifically, to an ultra high frequency reiiex tube of the general type disclosed in Fig. 2 of prior Patent No. 2,250,511, issued July 29, 1941, in thenames ol Russell H. Varian and William W. Hansen, for Oscillation stabilization system, and Fig. 13 of Patent No. 2,259,690, issued October 21, 1941, in the names of John R. Woodyard, William W. Hansen and Russell H. Varian, for High frequency radio apparatus.

Prior art devices of this type show no means whereby electrical automatic tuning of the attached resonators may be readily accomplished inside of the vacuum tube itself. These prior art tuning devices generally involve distortion of the shape of the attached resonator to produce the required change in the grid spacings of the resonator. The present invention affords a method of electrically tuning the frequency of such resonators, the entire tuning means being adapted for enclosure inside of the vacuum envelope of the tube itself.

It is further, observed that prior methods of tuning reflex tubes generally change the distance from the entrance grid to the reflector plate-by the amount that the distance between the entrance and exit grids of the resonator is changed, the distance from the exit grid to the reflector remaining substantially constant. Furthermore, the frequency is also changed by the displacement of the grids; the net eiect is to change the transit time of the electrons in making their round trip excursion, usually expressed in terms of the number of periods or cycles of the operating frequency. Theory and experiment show that such a change causes the power output of such a device, when used as an oscillator, to have a maximum value at one frequency, and to fall off at a rapid rate on either side of that frequency. In order to obtain a useful reflex oscillator (or mixer, etc.) to which automatic electrical fre-- quency control may be applied, it is desirable that the output of the device be maintained constant over as broad a range as possible.

It is, therefore, an object of the present invention to provide a novel construction ofxultra high frequency reflex tube structure in which the energy output is substantially constant over a large frequency range.

A further object is to provide such a tube structure in which the number of cycles of the transit time of the electrons is maintained substantially constant as the frequency is changed.

Yet another object is to provide such an elec- 31 Claims. (Cl. Z50-27.5)

tron beam tube device in which the spacings be` onator grid spacings and thus to vary or adjust the operating frequency of the device.

Another object of the invention is to provide a device of the type described wherein all elements including the tuning means :may be inserted in a compact vacuum envelope provided with a single base through which al1 leads, including the concentric line output lead, may extend.

A further object is to provide an electro-mechanical tuning device for such an electron tube ln which tuning of the tube is eiected by thermal expansion of a wire or strut means through which an electric current is passed.

An object of the invention lies in the provision of bimetallic or other means for accomplishing tuning of such a tube.

A final object is to provide such a device, en-

tirely enclosed in a vacuum envelope, so that ilexible diaphragms provided for tuning of the resonators do not have atmospheric pressure loading on one side, thereby enabling very thin and easily iiexed diaphragms to be used, so that considerably less power and devices of little: complexity may be used to effect tuning.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is an elevation cross-section view form of the present invention.

Fig. 1A is a fragmentary perspective view of a slight modification of Fig. 1.

Fig. 2 is a plan partial cross-section view of the device shown in Fig. 1 taken along the line Fig. 3 is a portion of the device of Fig. 1, viewed from the line 3-3 of that ligure.

Figure 4 is an explanatory diagram.

Fig. 5 is a perspective view of the grid structure in the resonators of Figs. 1 and 7.

Fig. 6 is a fragmentary view of an alternate form of the grid structure shownin Fig. 1.

of one Fig. 'I is an elevational partial cross-sectional view of a somewhat modied form of the invention.

Fig. 8 is a fragmentary elevational view taken at right angles to the plane of Fig. '7.

Fig. 9 is a fragmentary elevational partial cross-sectional view of an alternate form of the structure of Figs. 1 and '7.

Fig. 10 is an elevation partial cross-section view of a more general form of the invention.

Fig. 11 is a cross-section view of a detail of Fig. 10.

Similar characters of reference are used in all of the above iigures to indicate corresponding parts.

Referring now to Fig. 1, there is seen a crosssectional view of one form of the present invention. Electrons emitted fromthe heated cathode surface 6 are projected by an accelerating voltage through the grid and pass through an ultra high frequency eld in the region between grids 4 and 5 (which form part of a cavity resonator I) and are consequently velocity modulated. The beam passes out of the resonator I, and travels toward the reflector plate I5, which is usually maintained at or near the potential of cathode 6, so that the beam is reilected near plate I5 to return through grid 4. During the interval of time the electrons travel in the space between grid 4 and reflector plate I5 the velocity modulation of the beam has resulted in subsequent density modulation or grouping of the electrons of the beam. The inter-electrode distances are adjusted in a manner shown in the aforementioned patents so that these electron groups arrive in the region between grids 4 and 5 at a time at which they give up energy to the oscillating electric field between these grids, and thus maintain ultra high frequency electromagnetic oscillations in the resonator I. As is well known, variation of the spacing between grids 4 and 5 adjusts the resonant frequency in resonator I.

Referring to Fig. 4, there is shown schematically the principal electrodes of such a device; namely, the cathode surface 6', the entrance grid 5', the exit grid 4', and the reflector plate I5'. Let the distance between cathode l' and grid 5' be assumed constant and of value, K, and call that between grids 4 and 5', a, and that between grid 4 and plate I5', b. Then, the following illustrative analysis is approximately true. Assuming n is the number of cycles at the output wavelength A of resonator required for the electrons of the beam to leave grid 4', traverse their round trip path within the reflection space b and return to grid 4'; and assuming that the potential of reflector plate l5' is a constant, then n-b/)\. But it is found that A-\/c, over any given small range of A, where C is the elective capacity between the grids 4', 5', or A-I/\/a. Therefore n-b\/E, i. e., n=lc b VE where k is a proportionality constant. For innitesimal changes in the quantities n, a, and b:

dividing through by n We get Assuming that for frequency adjustments the plate I5' moves with grid 5', i. e., I5' and 5' have no relative motion with respect to each other but 4' has relative motion with respect to 5' and I5', then db=daz In order to maintain the optimum phase relationship between the electron bunches returning to the resonator and the oscillating field in the resonator the quantity if 1t should equal zero. 'I'hus is zero for a xed transit time, which is produced, and the output of resonator I is compensated, when:

bg2a (3) Obviously n could be determined from a plane other than 4', if desired, such as a plane midway between 4 and 5 in which case the constant 2 of Equation 3 would change while still being independent of the values of a and b. It may be` proven that for finite increments in n, a, and b, that the Equation 3 is substantially true to a rst order if all of the bunching is assumed to occur in the space b and none in the space a. Due to the fact that some bunching of the electrons actually occurs in the space between grids 4', 5', and also due to the fact that the time spent between grids 4', 5' constitutes a finite contribution to the total transit time of the electrons, it is found that for actual compensation, the value of b may vary over the range 3a b a.

Thus, in Fig. 1, a preferred form of the invention may have the distance between grid 4 and plate I5 twice that between grids 4 and 5.

Resonator I consists of frusta-conical apertured conducting reentrant portion 3, and flexible diaphragm I0 supporting portion 3 concen trically in a truncated conical region in resonator body 2. the resonator is centrally apertured to contain exit grid 4 opposite to entrance grid 5 in portion 3, and is supported rigidly in the vacuum envelope I2 by the outer tubular conductor 9, which is xed in an aperture in the resonator wall. The grids 4 and 5, as shown in Fig. 5, consist of alternate short and long radial round conducting grid bars 45 and 46 inserted in the round orifices in members 2 and v3 preferably flush with the conducting surface on which. the ultra high frequency currents flow.

Tube 9 cooperates with loop II and inner conductor 36 to form a concentric line terminal post for the removal of ultra high frequency energy from resonator I. Concentric line 9, 36 may be sealed by glass to metal seal 33 to provide continuity of the vacuum enclosure, and may be provided with any type of joint means such as bushing 34 provided with threaded flange 35, to which may be attached a concentric transmission line leading to utilization apparatus. Symmetrically `surrounding and parallel to tube 9, as seen in Figs. 1 and 2, are eight vertical conducting leads I4, I1, 31, 38, 39, on which are mounted various elements of the device and which act as electrical leads to furnish voltages to these elements.

The outer conducting portion 2 ofv Resonator portion 3 is fixed in position relative to portion 2 by means of struts 44, 44', as seen in Fig. 2, which are directly fastened to insulator plate I3, which may be of any ceramic material. Plate I3 is in turn Ixedly mounted on the two vertical conducting rods I4. Plate I3 is apertured to support heatshield 1, containing emitter surface 6 and heater element 1', to which current is supplied by leads 40, 4I, attached to respective conducting rods 39, that pass through the base of the vacuum envelope. Insulator plate I3 also supports focussing shield 8, mounted concentrically with respect to heat shield 1, and projecting toward entrance grid 5 beyond the heat shield.

Getter 42 is preferably placed near cathode E, and is flashed immediately before or after final seal-off of the tube from tip 29 by applying the appropriate voltage between one of the leads I4 and lead 38. Reflector plate I5 is shown positioned at a distance from grid 4'substantially twice that between grids 4 and 5, by struts I6, I5' attached to lead rods I1, which pass through the base of vacuum envelope I2.

The rods I4, I1, extend upward above resonator I to an equal level, and have their upper ends threaded and rigidly fixed relative to each other in insulating plate I8 by nuts and washers 20, 2 I, as seen in Figs. 1 and 3. On the upper surface of insulator I8, which may be of mica, is also fastened a metal plate 22 connecting rods i4, and having a curved projection 22 projecting upwardly from it. A biasing spring 23, which may be of tungsten connects projection 22' to a yoke 24, whose two ends pass through an aperture I9 in plate I8 and are fastened rigidly on either side of resonator wall 2. If desired, the spring 23 may be connected between yoke 24 and rods l1, in a similar manner. This is shown in Fig. 1A, in which plate I 22, corresponding to plate 22 of Fig. 1, is supported by posts I1 and is urged toward resonator body 2 by tension spring 23 hooked into projection lug |22' formed on plate I2?. Wire 25 may pass freely through an opening in lug i222 as shown. Spring 23, in the position shown in Fig. l, normally counteracts the stiffness of the diaphragm tu; but if diaphragm III is made resilient enough, spring 23 need not beused. A thin plate 3@ is spot-welded directly in a central position opposite projection 22 to the metal plate 22 in such a manner as to clamp a wire 25, which may be of tungsten, to the plate 22. The wire 25 extends from the plate 22 through a tubular projection 26 sealed into the side of the vacuum envelope of the tube andv extends through a glass to metal seal in the outer end of that projection. The end of the wire extending through the seal may be soft-soldered into a conventional grid cap 21, as at 28.

In operation, a current is passed through the wire 25, heating the wire and changing its length. The position of the end3ii of the wire is seen to be related to the amount of current passed through the wire. A portion of the motion of the end of the wire is transmitted through rod I4, plate I3, rods 44, 44' to the entrance grid 5. Also, it is seen that the reflector plate I5 moves in the same direction by an amount equal to the motion of grid 5 due to the connections shown. Thus, by running more or less current through the wire 25, any desired spacing of the grids 4, 5 may be attained, thus varying the resonant frequency of resonator I over a considerable free quency range. Also, since the proper spacings have been chosen between grids 4 and 5 and between reector I5 and grid 4, the output of the tube remains substantially constant.

Since element 25 is a wire, bias spring 23 is naturally a compression spring which expands upon heating 'of wire 25 to effect separational relative displacement of grids 4 and 5. Therefore, electrically energized thermally responsive element 25 and spring 23 obviously cooperate to positively control tuning of the resonator.

Plates 3l are spot-welded along the edges of support rods I1, and likewise plates 32 are welded along `edges of support rods I4.

Without the plates, the rods bend under action of the tuning wire 25 as a cantilever does; but with the stiftening plates. the length of the rods I1, I4 welded to the plates moves as a lever, the remainder of the rod lengths above and below the stiflening plates deforming as a. cantilever. 'I'he function of these plates is to stiften the rods along the length of the plates so that if the upper portion of the rods is moved by a nite amount, the middle portion of the rods will move by an amount greater than if the stiffening plates 3|; 32 were not used. It is seen that any desired ratio of free rod length to stiiened rod length may be used.

In Fig. 6 is illustrated an alternate form of grid arrangement useful in the device of Fig. 1. The grids 4 and 5 arerplaced as before flush with the surfaces carrying ultr`a high frequency current in the resonator. For very short wavelength outputs from such resonators, the distance between grids 4 and 5 is very small, so that the distance from grid 4` to reflector plate I5 may be very nearly equal to the thickness of the wall 2 of the resonator. If a third grid41 of the same type las grids 4 and 5 is placed flush with the surface of wall 2 opposite grid 4, the space between the surface 2' and the reector grid can be increased, due to the eld free space between grids 41 and 4.

A modification of the device shown in Fig. 1 is seen in Fig. '1, in'which the use of the projection 2E in the side of the Vacuum envelope I2 of the tube of Fig. 1 is avoided. The wire 48 is now allowed to pass over a yoke 5I as seen in Figs. '1 and 8,-this yoke being spot-welded tol each side of the resonator 2. The wire 48 lies in a slightly concave neck of the yoke 5I in the apex of that yoke and then passes directly downward to the lead-in conducting rod 31 which passes through the base of the vacuum envelope I2 of the tube. The operation of this device is seen to be similar to that of Fig. 1. The wire 25 of Fig. 1 and the wire 48 of Fig. 'I may be operated in compression, if desired, as well as in tension as shown in these figures. In such case, the wire is made thicker and stiffer, as in the form of a strut.`

In Fig. 9 there is shown an alternate thermalmechanical mechanism for securing the desired inter-electrode relative motions. In this gure a flanged metal plate 52 is riveted to the insulating plate i8. A circular bimetallic element 55 is riveted to the flange Eitof this plate which element carries a heater coil 55 supplied with necessary current through leads 51 and 551. The op-` posite end of the bimetallic element 55 is fixed to the wall of resonator 2 against insulating block 59 by means of screws B0. The structure and operation of this device is again seen to be similar to that of Fig. 1. i

The general conclusions that are obtained from the theory resulting in Equation 3 are seen to be of only approximate correctness and it is also seen that effects due to bunching in the resonator 7 space, space charge, secondary electrons, etc., were entirely neglected. Because of these last named effects and under circumstances where b cannot be made approximately equal to 2a because of constructional diiiiculties it can be shown that it is not always desirable to move the reflector plate at exactly the same rate as the entrance grid is moved. The structure shown in Fig. provides a device for accomplishing this relative dinerence of motion. Instead of connecting the upper ends of rods Il and I1 directly together as in the previous figures, the rods are now connected so that the upper ends of rods Il move at a fraction of the rate at which the upper ends of rods El move. This is accomplished in the following manner. At some distance below the upper ends of rods il are attached insulating blocks 65. Near the upper endsof rods I4 are attached similar insulating blocks 61. Tw'o wires 66, normally in tension, are ilxedly attached at their ends to the insulatin blocks 65 and 61 as shown in Fig. 11.

In Fig. 10, the thermal-mechanical device which causes the motion of the electrodes is shown as a bimetallic element 55' attached to and insulated from the resonator 2 and having its other end attached directly to the rods I1. The heater element 56 for the bimetallic strip 55' is provided with a voltage through the outer conductoryof concentric line 9 and through lead 5T, and through lead-in lead 31 attached to rod 58. It is readily seen that the wire 66, if made stii enough, may be made to operate in compression as well as in tension. Where wire 66 is iexible, spring 23 is a compression spring to maintain wire 66 in tension. Where wire 66 is stiff, spring 23 may be a tension spring as shown to take up slack or may be omitted.

It is evident that other types of mechanical, electrical, or other tuning device, insidev or out side of the vacuum envelope, may be used to accomplish the described desired inter-electrode relative motions. It is also evident that any desired group of elements of the device may be held in constant position, and that any element or group of elements may be held stationary in producing the desired result.

As 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. A high frequency tube structure comprising means for producing an electron beam, a hollow resonator having entrance and exit means through which said beam is adapted to pass, a reflector positioned beyond said exit means for reflecting said beam back into said hollowresonator, and adjustable tuning meansconnected to said resonator and reflector for actuating said entrance means and said reflector simultaneously.

2. A high frequency tubel structure as defined in claim 1 wherein said tuning means comprises a thermo-responsive element connected to said entrance means and said reflector.

3. A high frequency tube structure comprising means for producing an electron beam, a hollow resonator having entrance and exit means through which said beam is adapted to pass, a reflector positioned beyond said exit means for reflecting said beam back into saidhollow resonator, ad- ,instable tuning means comprising a thermo-responsive element connected to said resonator and reflector for actuating said entrance means and said reflector, and electrical means for effecting the heating of said thermo-responsive means.

4. A high frequency tube structure comprising a hollow resonatorhaving entrance and exit grids, means for setting up an electron stream for passage through said grids in succession, a reflector positioned beyond said exit grid for reflecting electrons of said stream back into said resonator,

mechanical transmission means interconnecting said entrance grid and said reflector, and means embodying a thermally contractible and extensible member connected to said mechanical transmission means for effecting simultaneous movement of said entrance grid and reflector to thereby change the operating frequency of said resonator while at the same time maintaining its energy output substantially constant.

5. A high frequency tube structure comprising, means for producing an electron beam, a.

hollow resonator within said structure adapted to contain standing electromagnetic waves and having beam entrance and exit openings through which said beam is adapted to pass, a reflector positioned beyond the exit opening for reflecting said beam back into said hollow resonator, and variable tuning means operably connected to said reector and said resonator for producing relative motion between said reflector and entrance vthe resonant frequency` thereof, and means in said` structure for maintaining a xed phase relationship between the returning groups of electrons reentering said resonator after reflection and the alternating field between said electrodes regardless of the adjustment of said tuning means.

7. Apparatus as in claim 6, wherein said lastnamed means directly couples one of said pair of electrode to said reflector electrode to provide simultaneous displacements thereof, and wherein said frequency-varying means includes means for adjusting the separation of said pair of electrod.

8. Apparatus as in claim 6, wherein said lastnamed means comprises means coupling said reector and one of said electrodes to provide proportional unequal displacements thereof.

9. High frequency tube structure comprising means defining a hollow resonator having opposed relatively movable electron permeable wall portions, means adjacent said resonatorfor projecting a beam of electrons through said wall portions, a` reflector electrode in the path of said beam for returning said electrons into said resonator, means coupled to said wall portions for controlling the spacing between `said wall portions for tuning said resonator, and means interconnecting said reflector electrode and that one of said wall portions which is first traversed by said electron beam to maintain said reflector electrode and said one wall portion spaced a fixed distance apart.

10. High frequency tube structure comprising a hollow resonator having exibly interconnected wall portions formed with spaced aligned electron permeable regions, means in said structure for projecting a beam of electrons through said resonator, a reector positioned in the path of said beam to return said beam into said resonator, adjustable means relatively displacing said wall portions for varying the spacing of said regions for tuning said resonator, and motion transmitting means between one of said wall portions and said reilector for moving said reflector concomitantly with said one wall portion but through a different distance than said one wall portion.

11. High frequency electron discharge apparatus comprising means for producing a beam of electrons, a pair of electrodes in the path of said beam and deiining a gap therebetween, tuned circuit means coupled to said electrodesto provide an alternating electric eld across said gap for velocity modulating said electrons, a reector electrode in the path of said beam beyond said electrodes for reversing said electrons, whereby they reenter said gap in grouped condition, a thermally-energizable extensible member operably coupled between said reflector and one of said electrodes, and means in said apparatus for supplying heating energy to said member to produce change in the extension thereof, whereby the spacing between said reiiector and said one electrode is varied.

12. Apparatus as in claim 11, wherein said member comprises a flexible wire rigidly xed at one end with respect to said reector and rigidly xed at the other end with respect to said one electrode, and further including resilient means maintaining said wire in taut condition.

13. Apparatus as in claim 11, wherein said member comprises a bi-metallic element having one end connected rigidly to said reflector and the other end connected rigidly to said electrode.

14. Apparatus as in claim 11, wherein said member comprises a thermally extensible rigid strut having one end rigidly xed with respect to said reflector and having the other end rigidly fixed with respect to said one electrode, said enorgy-supplying means comprising means coupled to said strut for passing heating current therethrough to vary the extension thereof and thereby to vary the separation between said reflector and said one electrode.

l5. A thermionic tube structure comprising an evacuated insulating envelope, a hollow resonator supported within said envelope and having opposing apertured walls for receiving an electron beam, said resonator having a ilexible wall portion interconnecting said opposing apertured walls, means for producing an electron beam for projection through the apertured walls of said resonator, a reflector plate positioned adjacent said resonator for reflecting said electron beam back into said hollow resonator, rods extending within .said envelope and carried by the latter, one of said rods being connected to one of said opposing apertured walls, another of said rods being connected to said reiiector plate, a member interconnecting said rods, and thermally responsive means connected to said interconnecting member for actuating the same to thereby effect simultaneous tuning movement of said one apertured wall and said reflector plate relative to the other apertured wall.

16. A thermionic tube structure as defined in claim wherein said thermally responsive me ans comprises a bimetallic element connected to said interconnecting member and to the other apertured wall of said resonator, means anchoring said other apertured wall within said evacuated envelope, and exteriorly controllable means4 in said tube structure for heating said bimetallic element.

17. A thermionic tube structure comprising an evacuated envelope, a hollow resonator comprising opposing apertured walls and a ilexible interconnecting wall portion therebetween, means rigidly supporting one of said apertured walls ,y

within said evacuated envelope, means within said envelope for projecting an electron beam through the apertured walls of said resonator, tuning means within said envelope connected to one of said apertured walls for effecting relative movement between said apertured walls by the ilexure of said exible interconnecting wall portion, and electrically energizable control means operably coupled to said tuning means, said electrically energizable means being operable from without said evacuated envelopefor controlling said tuning means. i

18. Athermionic tube structure as defined in claim 17 wherein said tuning means comprises mechanical transmission means for exerting a force between said opposed apertured wall portions, and said transmission means includes an electrically heated thermally responsive element.

19. Thermionic tube structure comprising an evacuated envelope, a hollow resonator within said envelope comprising opposed apertured walls and a iiexible interconnecting wall portion therebetween, means within said envelope for projecting an electron stream through the apertured walls of said resonator, tuning means within said envelope connected to said apertured walls for effecting relative movement therebetween. by the flexure of said iiexible interconnecting wall portion, said tuning means including a thermally responsive expansible and contractible member within said envelope determining the separation of said apertured walls, and electrically energizable control means operable from outside said evacuated envelope for controlling the extension of said member to correspondingly tune said resonator.

20. Ultra high frequency apparatus comprising an evacuated envelope, means within said envelope defining a hollow resonator having a shiftable element for varying the natural frequency of said resonator, an elongated resonator tuning member having a dimension variable in response to electric current ow therethrough, and means operably connecting one end of said member to said shiftable element with the other end of said member anchored with respect thereto, to provide tuning movement of said element when the length of said member is varied by said current.

21. Ultra high frequency apparatus comprising an envelope, means within said envelope defining a hollow resonator having a displaceable wall portion for varying the natural frequency cf said resonator, an expansible and contractible elongated thermally responsive tuning member within said envelope having one end substantially anchored within said envelope and its other end operably connected to said displaceable wall portion, and resilient means coupled to said member for opposing displacement of Said wall portion in one sense.

22. High frequency tube structure comprising a hollow resonator having a shiftable wall portion for tuning said resonator, a cantilever connected intermediate its ends to said wall portion, and a thermally responsive expansible and contractible tuning member operably connected to the free end of said cantilever.

23. The tube structure detlned in claim 22, including means on said cantilever for resisting bending thereof over a predetermined part of its length.

24. High frequency apparatus comprising a hollow resonator having a shiftable element for varying tuning thereof, a cantilever connected intermediate its ends to said element, and an electrically controllable expansible and contractible tuning member operably connected to said cantilever near the free end thereof.

25. A velocity-modulation tube comprising an evacuated envelope having disposed therein an electron emitter for producing an electron beam, a cavity resonator having electron beam entrance and exit grids, a exible diaphragm forming one wall of said resonator and supporting said exit grid for relative movement toward and'from said entrance grid, a fixed 'electron-reflecting electrode disposed oppositesaid exit grid in the path of said beam, and electromechanical tuning means attached to said exit grid, said tuning means being adapted to move said exit grid on the one hand perpendicularly toward and from said entrance grid and said electron-reflecting electrode on the other hand. f

26. A thermionic tube structure comprising an evacuated envelope, a hollow resonator supported within said envelope and having opposing apertured Walls for receiving an electron beam, said resonator having a iiexible wall portion interconnecting said opposing apertured walls, means opposite one of said walls for projecting an electron beam through the apertured walls of said resonator, a reector plate within said envelope positioned in the path of said beam for reecting said electron beam back into said hollow resonator, tuning means within said envelope for adjusting the separation of said apertured wall portion by exure of said ilexible walls to tune said reso-y nator, and lead means connected to said beam projecting meanasaid resonator, and said reiiector plate, and extending outwardly of said envelope for supplying control potentials to these elements.

2'?. A thermionic tube structure comprising an evacuated envelope, a hollow resonator supported within said envelope and having opposing apertured walls for receiving an electron beam, said resonator having a exible wall portion interconnecting said opposing apertured walls, means opposlte one of said walls for projecting an electron beam through the apertured walls of said resonator, a reflector plate within said envelope posiing relative movement between said unit and the A otherk apertured wall to effect tuning of saidresonator, and lead means connected to said beam projecting means and said reflector plate, and extending outwardly of said envelope for supplying control potentials to these elements.

28. High frequency tube structure comprising an envelope, a plurality of substantially parallel rods within said envelope, a hollow resonator mounted within said envelope, means adjacent said resonator for projecting a beam of electrons through said resonator, a reflector electrode mounted upon one of said rods and located in the path of said beam to return said electrons into said resonator, and means securing said resonator to one of said rods.

29. High frequency tube structure comprising an evacuated envelope, a plurality oi substantially parallel rods within said envelope, a hollow resonator having exibly interconnected wall portions mounted within said envelope, means securing one of said wall portions to one of said rods, means securing the other of said wall portions to said envelope, means in said structure for projecting an electron beam through said resonator, and a reflector electrode in the path of said beam for returning said beam through said resonator and secured to one of said rods.

30. High frequency apparatus as in claim 31, wherein said reiiector spacing is substantially twice the length of said gap.

31. High frequency electron discharge apparatus comprising means forproducing an electron stream, a pair of electron-permeable electrodes in the path of said stream defining an axially extending gap, tuned circuit means coupled to said electrodes, whereby an alternating electric eld may be set up between said electrodes for velocity modulating said stream, a reflector electrode in the path of said stream beyond said electrodes for reversing the electrons of said stream to reenter said gap, the spacing of said reflector from the adjacent one of said electrodes being larger than but less than three times the spacing of said electrodes.

SIGURD F. VARIAN. DONALD R. HAMILTON.

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