US2440089A - Electron discharge device employing cavity resonators - Google Patents

Description

April 20, 1948. I v, HAEFF 2,440,089

ELECTRON DISCHARGE-DEVICE EMPLOYING CAVITY RESONATORS Filed Aug 18, 1942 3 Sheets-Sheet 1 WENTORKfl ATTORNEY April 20, 1948. r A. v. HAEFF ELECTRON DISCHARGE DEVICE EMPLOYING CAVITY RESONATORS 5 Sheets-Sheet 2 R my M m m km 0%. F W mm w W I WM W Q 1:: mm J xi 9 a I \\H W .3 I & 2 v 3 w m \wwmw hw I a QM \h Mshm Q AIY, R. D N8 Wm m hm mg mg v T 0m. WV

ATTORNEY April 20, 1948. A. v. HAEFF 2,440,089

ELECTRON DISCHARGE DEVICE EMPLOYING CAVITY RESONATORS Filed Aug. 18, 1942 3 Sheets-Sheet 3 I L E Q:T w 56 Q r a I o \l I k 155 M 62 6 1 1 54 .55 l i: I Y

- E 5.9 61 J19 m 'r i INVENTOR ATTORN EY Patented Apr. 20, 1948 ELECTRON DISCHARGE DEVICE .EMPLOYm G CAVITY RESONATORS Andrew V. Haefl",

Washington, D. 0., assignor to Radio Corporation of America,.a corporation of Delaware Application August 18, 1942, Serial N 0. 455,175

15 Claims.

My'invention relates to electron discharge devices and their associated circuits particularly useful at ultra high frequencies.

In one form of crating electrodes spaced apart to provide a gap past which the electrons move from the grid to the collector. Surrounding the envelope is, a resonant cavity circuit or resonator of annular or doughnut shape having a gap registering with the gap between the tubular electrodes and surrounding the envelope close to the envelope wall and lying in a plane transverse to the. electron stream. The electrons modulated by the grid and formed into groups of'electrons pass across the gap of the resonator and cause the resonator to be energized by induction, the electrons being collected by the collector. When used as an oscillator, energy is 'fed back from the resonator to the-input circuit connected between the oathode and the grid. To insure the voltage which is fed back must be in the correct phase with respect to the input voltage so that losses in the input circuit are compensated for and the oscillations sustained. Due to the length of the path travelled by the electrons and, consequently, due to the finite transit time of the electrons, and various other factors, it is not always possible with the usual means to adjust the phase of the voltage fed back correctly for most eilicient operation.

In the type of electron discharge device described, utilizing resonators, maximum power output and efiiciency would result if; each group of electrons before its passage past the output gap of the output resonator is compressed by application of a velocity modulation potential so as to provide dense groups of small dimensions in the direction of travel of the electrons, and these densegroups made to pass the output gap at the instant of time. at which the high frequency voltage across the gap is of such sign and value 'asto cause a maximum amount of deceleration to each group of electrons.

It is, therefore, an object of. my invention to providean electron discharge device and circuit 2. coupling means for independently controlling the phase and magnitude of the feedback voltage.

Another object of my invention is to provide a device of the type described and in which the efiiciency of operation is improved by compressing electron groups prior to their passage across the output gap.

More specifically itis anobject of my invention to provide an electron discharge device and circuit arrangement by means of which a compressing voltage of the correct phase and amplitude influence the electron stream prior to the passage of the electrons past the output resonator gap.

These and other objects will appear hereinafter;

The novel features which I believe to be characteristicof my invention are set forth with particularity in the appended claims, but the invention will best be understood by reference tothe following description taken in connection with the accompanying drawing in which- Figure 1 is .a longitudinal section of an ultra high frequency electron discharge device and circuit made according to my invention;

Figure 2 is a longitudinal section of a modification of the device shown. in Figure l and its as sociated circuit;

Figure 3 is a diagram showing the method of operation of electron discharge devices and the associated circuits made according to my invention and shown in Figures 1 and 2;

Figures 4, 5 and 6 show struction of the adjustable feed back transmission line utilized in the apparatus shown in Figures I and 2.

Referring to Figure 1, an tube and associated circuit my invention includes the elongated evacuated envelope 9 having at one end a concave surface indirectly heated cathode I 0 and a cup-shaped grid H having a foraminous portion of the same shape and closely spaced from cathode H) and formed toshl'eld thecathode from' the other electrodes within the tube. Positioned at the other endof the envelope is a collector Ilprovided'with the secondary electron suppressor electrode I3. Positioned between the grid and the collector are the accelerating electrodes l4 and IS, the electrode l4 being elongated and providing an essentially field-free space within its center portion. Electrodes l4 and [5 also serve as screening electrodes between theoutput gap and other electrodes of the device.

The cathode circuit comprises the hollow conelectron discharge madeaccording to the details of the con fixed potential.

ductor l6 surrounded by the conductor l1, thus forming a coaxial line. The cathode is supported by the leads and conductors l8 and I9 which are connected respectively to the conductor l8 within a hollow member I6 by a springclip arrangement, and to the exterior of the conductor- Hi. The conductor l8 serves as a heater lead and the conductor 19 as a cathode and heater lead. The end of the concentric line arrangement is closed by a disc member 2| slidably positioned on a conductor l6 and manipulated by an insulating member 2|, a space being provided between the element 2| and the outer conductor ll. By this arrangement the coaxial line is closed for radio frequency currents in effect providing a tunable resonator but the inner conductor it and the outer conductor I! may be maintained at different fixed potentials. The grid circuit includes the inner conductor 22 and the outer conductor 25. The grid lead support 23 is capacitively coupled to the conductor 22 by means of the arrangement shown at 22', but a lead 24 is connected to conductor 23 to permit a biasing voltage to be applied to the grid il. A closure conductor 25 longitudinally slidable on the conductor 22 is manipulated by an insulating handle at 21. Thus a closed tunable coaxial line resonator is provided for the grid circuit. v

Thus, the grid line as well as the cathode line can be separately tuned, and the cathode circuit completely isolated from the other circuits as described more fully below.

The output tank circuit comprises a cavity resonator 28 placed coaxialy with the tube and having a gap 32 surrounding the envelope, the gap lying in a plane transverse to the electron stream. Modulated electrons passing across this gap excite the resonator 28 in a manner now well known and described in my United States Patent No. 2,237,878, issued April 8, 1941, and assigned to the same assignee as the present application.

A second resonator having a gap surrounding the electron path between the resonator 28 and the grid comprises the outer conductor 32 and the inner conductors 32 and 32" closed at one end by the slidable ring-like member 33 and provided with a gap 33 which registers with the gap between the grid H and electrode M. Electrode I4 is electrically connected to the member 32 by radially directed conductors 29. The capacitance between the conductor 32' and the cylindrical surface of the grid ii provides a low impedance for high frequency currents between these elements, 32' and H. Movement of the closure member 33 tunes the control grid-accelerator electrode circuit. Capacitive coupling between the element 32 and the wall of resonator 28 is made by means of the collar 3| to provide a closed control grid-accelerator resonator while at the same time permitting the output resonator 28 to be at a different, preferably higher, The control grid-accelerator electrode resonator when excited by the modulated stream provides. compression of the electron groups in a manner to be described below, this compression taking place prior to the passage of electrons across the gap in the output resonator 28.

In order to provide feedback of energy from the output resonator to the input circuit in proper phase, I provide a coaxial feed line adjustable in length and coupled at its ends to the resonator 28 and the cathode coaxial line circuit. Surrounding the resonator 28 is a conducting collar 36 capacitively coupled to the resonator, and insulated therefrom by insulator collar 37. The adjustable coaxial transmission line consists of inner conductor 39 and outer conductor 40, the transmission line being provided with a coupling loop 38 within the output resonator and a capacity couplingelement 4.! supported on the inner conductor of the coaxial resonator of the cathode circuit. Intermediate the ends of the coaxial feed line is a so-called trombone slide arrangement comprising the elements 39' and 42', details of which are shown in Figures 4, 5 and 6 and which will be described in greater detail below. This permits the physical and consequently the electrical length of the transmission line to be varied to insure proper phase of the energy fed back to the cathode circuit and consequently of the voltage developed between the grid and the cathode.

The output is taken from the output resonator 23 by means of a coupling loop 35. The cathode heater voltage is supplied by voltage source 42. The proper bias on the grid is obtained by the resistor 43 in the cathode circuit andthc resistor 44 connected to the grid lead. High positive voltage for the resonator 28 and the accelinitially passing across crating electrode Hi and [5 is supplied by a voltage source 45. The collector is maintained at a lower positive potential than the tank circuit by means of the voltage source 46, the suppressor electrode l3 being at a still lower positive potential than the collector.

Operation of the device, particularly with regard to voltage and current phase relationship and to the action of the compression circuit, can be explained by referring to Figures 1 and 3. The grid H is biased negatively with respect to cathode lil so that the electrons flow from the cathode and through the grid only during the positive half cycles of the radio frequency voltage existing between the cathode and the grid.' In Figure 3, the curve designated vg-c represents the grid-cathode voltage and the curve Ipi represents the current passing through the grid H. As shown there is a small time lag between the volt-age peak and the electron current peak which can be ascribed to the transit time of the electrons between the cathode l0 and the grid I I. The current Ipl passing through the gap 34 will excite the compressor circuit, which is the control grid-accelerator resonator 32, so that a voltage Vgs will be developed across gap 34. The voltage across the gap 35 will be shifted in phase with respect to current Ipl is the compressor circuit is tuned oil-resonance as indicated by curve Vgs of Figure 3. This phase shift is such that the first electrons of the group passing across the gap 34 begin crossing the gap when the radio frequency voltage across the gap is in a direction to oppose movement of the electrons across the gap but increases in a positive direction so that the last electrons crossing the gap are accelerated to the greatest extent. Since the electrode L4 is at a positive potential with respect to grid ll, there is a constant accelerating field across the gap 34. The radio frequency voltage applied by the control grid-accelerating electrode resonator across the gap 34 and which is alternating is superimposed on the fixed accelerator voltage to successively increase or decrease the resultant accelerating voltage. The result is that the electrons of each group are continuously variably accelerated; the last electrons crossing the'gap being accelerated to agreater extent than those the gap. The electrons then. pass within the electrode electrons so pressed. In

the grid circuit is tuned so:

proper can be made substantially zero.

feedback transmission line.

M and member 32-" within which there is an essentially fieldfree space, before reaching the R. F. field across the gap 39.. The operating conditions areso chosen that as the group of electrons passes from the gap 34 to gap 30 and moves through the fieldfree space, the fast electrons overtake the slow that theelectron. group becomes com- Figure 3 these compressed groups are indicated by the deep shadowed areas Ipz. The Ipz curves as shown in Figure 3. are not related in time to the other curves of Figure 3. The

phase of. current l'pz depends on transit time between gap 34 and 33 during which time compression takes place. In other words he isnot necessarily in phase with vgs, as shown: in Figure 3. The phased feedback voltage and the operating potentials determining electron transit time through different sources are so adjusted that the compressed groups of electrons pass across the gap 35 at the instant of time that the voltage across gap is hasmaXi-mum decelerating effect. Hence there passes a dense charge in a very short period of time at the moment when maximum energy can be delivered to the decelerating field of resonator 28. Asa result more power is generated in the output resonator 28 than would be the case with only grid modulation.

In order to prevent coupling between the cathode input circuit and the compressor circuit, that the impedence between the inner conductor 32' of the control grid-accelerating electrode resonator and the grid This tuning is accomplished by means of. plunger 2E.

The cathode circuit is thus completely isolated and shielded from the remaining circuits. of the apparatus and the only coupling through the This prevents any undesired coupling between the control gridaccelerator circuit and the cathode circuit due to common impedances between these circuits. The size of the coupling loop Sui-s. chosen so as to extract from the output tank circuit 28: the amount of power just just SllffiCint to excite the cathode circuit to the desired amount. The cathode circuit lG-i'l is tuned to the operating frequency and the position of the coupling element along the line i5 is adjusted so that the impedance of the cathode circuit at the position Al is equal to the characteristic impedance of the feedback transmission line 39-4il. Under this condition the phase of the feedback voltage is determined solely by the length ofthe transmission line which is adjustable, and the magnitude of feedback voltage is determined by the size of the coupling loop 38.

A further improvement of my invention is shown in Figure 2, the same elements being designated by the same numerals in both Figures 1 and 2. In the modification shown in'Figure 2 an additional adjustable transmission line is connected between the output resonator 25 and the compressor resonator connected between the control.- grid ii and the accelerating electrode M. This serves two purposes, first, it insures that sufiicient energy is supplied to the control gridscreen. electrode cavity resonator, and, second, it makes, it possible to excite the compressor resonator in the correct phase for maximum compression even when this circuit is tuned to resonance at the operating frequency. The trans mission line comprises an inner conductor 49 and an outer conductor 55- with coupling loops 5| and 48, the adjustable portion being provided by the trombone slide arrangement 49! and 55'. The output of the oscillator is delivered to the useful load by means of a coupling loop 5| and a coaxial feed line 52 and 53-. The outer conductor 53 of this line is isolated from the resonator 28 by means of a by-passcondenser 54 in order to remove the resonator 28 voltage from the feed line. The operation of the apparatus shown in: Figure 2 is substantially that of the apparatus shown in Figure 1.

The details of the trombone slide arrangement are shown in Figures 4, 5 and 6. It comprises a box-shaped structure of rectangular cross sectlon l0 and inner conductors'39 and 39 formed of hollow tubular and solid rods, respectively. The inner tubular members are supported within the outer box-like structure 45' by insulating supports fill-and 51. The outer box-like structure 4!) is divided into two elongated parallel passageways by means of the conducting wall 62. and its extensions 50, 51, 52 and 53. The box-like structure is closed at one end by a partition 54. The members 50, 5!, 52 and 53 provide a partition similar in function to the solid wall 62, but separated in the middle for permittingmovement of the U-shaped element 55 which is connected to the rods 39'. To varythe length of the line, the inner conductors 39- are telescopically received within tubular members 39. Extensions 39' are secured and connected together electrically by means of the U-shaped element 5-5. connected and movable by means of the insulating arm 56 which is provided with guide fingers 57 sliding in the slots formed between the elements ill-51 and 52-53. The space between 59-5l and 52-53 is only great .enough to permit element 55 to slide between them without contact. Elements 50, 5|, 52 and 53 are ineffect extensions of wall 82 and serve to prevent leakage of R. F. fields from to another. Thus, the R. F. fields guided by the conductors 39, 39' travel along one passageway and along the conductor 55 enter another passageway and proceed along conductors 39 and 33. Thus the electrical length of the transmission lineis varied by varying only the portion of the inner conductor 39-55-39.

Anapparatus made according to my invention provides an improved oscillator useful at ultra high frequencies and one in which the einciency dicated but that many variations may he. made in the particular structure used and the purpose iorwhich it is employed without departingfrom thescope of my invention as set forth in the appended claims.

What I claim as new is:

1.. An electron discharge device having means including a cathode for supplying asbeam of electrons. means for receiving said electrons, a control grid between said cathode and receiving means for modulating said beam of electrons to provide spaced groups. of electrons when said grid is energized the beam of electrons for 7 by radio frequency voltage, an accelerating and screen electrode positioned adjacent said control grid, means coupled between said control grid and said accelerating and screen electrode for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group of electrons are accelerated to the greatest extent, means in the path of the electrons for providing a field'free space through which said accelerated groups of electrons are directed and in which compression of each group of electrons occurs and a resonator surrounding the path of the beam of electrons for inductively extractin energy from the compressed groups of electrons.

2. An electron discharge device having means including a cathode for supplying a beam of electrons, means for receiving said electrons, a control grid between said cathode and receivingmeans for modulating said beam of electrons to provide spaced groups of electrons when said grid is energized by radio frequency voltage, an

accelerating and screen electrode positioned adjacent said control grid, means coupling said control grid and said accelerating and screen electrode for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group of electrons are accelerated to the greatest extent, means in the path of the electrons for providing a field-free space through which said accelerated groups of electrons are directed and in which compression of each group of said electrons occurs and a resonator surrounding the path of inductively extractin energy from said compressed groups of electrons, and means including an adjustable feed back transmission line coupled between said resonator and said coupling means for transferring energy from said resonator to said coupling means.

3. An electron discharge device having means including a cathode for supplying a beam of electrons, means for receiving said electrons, a control grid between said cathode and electron re-v ceiving means for modulating said beam of electrons to provide spaced groups of electrons when radio frequency voltage is applied to saidcontrol grid, an accelerating and screen electrode positioned adjacent said control grid, means including a first resonator surrounding the path of the beam of electrons and coupled between said control grid and said accelerating V and screen electrode for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group of electrons are accelerated to the greatest extent, means in the path of the electron groups for providing a field-free space through which said electron groups are directed and in which compression of each group of electrons occurs and a second resonator surrounding the path of the beam of electrons for inductively extracting energy from said compressed groups of electrons.

4. An electron discharge device having means including a cathode for supplying a beam of electrons, means for receiving said electrons, a control electrode between said cathode and receiving means for modulating said beam of electrons, means coupling said cathode and control electrode for applying radio frequency voltage between said cathode and control electrode to provide spaced groups of electrons, an accelerating control electrode, means and screen electrode positioned adjacent said coupled between said control electrode and said accelerating and screen electrode for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group of electrons are accelerated to the greatest extent, means in the path of said electrons for providing a field-free space through which the groups of electrons are directed and in which compression of each group of said electrons occurs and a resonator surrounding the path of the beam of electrons for inductively extracting energy from said compressed groups of electrons, means including an adjustable transmission line coupled between said lastre'sonator and means coupled between said cathode and the control electrode for transferring energy from said last resonator to said means coupled between said cathode and control electrode.

5. An electron discharge device having means including a cathode for supplying a beam of electrons, means for receiving said electrons, a con-. trol electrode positioned between the cathode and receiving means for modulating said beam of electrons, a coaxial line connected to said cathode for applying a radio frequency voltage between said cathode and control electrode to provide spaced groups of electrons, an accelerating and screen electrode positioned adjacent said control electrode, a resonator coupled between said control electrode and said accelerating and screen electrode for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group of electrons are accelerated to the greatest extent, means in the path of the electrons for providing a field' free space through which said roups of electrons are directed and in which compression oi each group of said electrons occurs and a resonator in the path of the compressed grou of electrons for inductively extracting energy from said compressed group of electrons, means including a transmission line coupled between said last resonator and the coaxial line for transferring energy from said last resonator to said coaxial line.

6. An electron discharge device having means including a cathode for supplying a beam of electrons, means for receiving said electrons, a control electrode between said cathode and receiving means for modulating said beam of electrons, means coupled to said cathode for applying a radio frequency voltagebetween said cathode and control electrode to provide spaced groups of electrons, an accelerating and screen electrode positioned adjacent said control electrode, means coupled between said control electrode and said accelerating and screen electrode for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group of electrons are accelerated to the greatest extent, means in the path of the electrons for providing a field-free space through which said groups of electrons are directed and in which compression of each group of said electrons occurs and a resonator through which the groups of electrons are directed for inductively extracting energy from said compressed groups of electrons, means including a transmission line coupled to said resonator and said means coupled to said cathode for transferring energy from said resonator to said means coupled to said cathodaand another transmission line 'for transferring energy from said resonator to the means coupled between the control electrode and the accelerating and screenelectrode. l

7.'An electron discharge device having means including a cathode for supplying a beam of electrons, a control electrode and collector electrode, said control electrode being positioned between said cathode and collector electrode, a cavity resonator connected between said cathode and control electrode, and a cavity resonator positioned between'said control electrode and said collector for extracting energy from said beam of electrons, and a coaxial transmission line connected between said cavity resonators and including an elongated tubular structure, a partition extending along said tubular structure providing a pair of elongated adjacent parallel chambers opening into a passageway atone end, a tubular member within each of said chambers and extending longitudinally of said chambers but out of contact with the tubular structure, and a U- I shaped element telescopically engaging and connecting said tubular members and extending through said communicating passageway, said U-shaped member being movable to vary the length of the coaxial transmission line.

8. An electron discharge device having means including a cathode for supplying a beam of electrons, a control electrode and a collector electrode, said control electrode being positioned between s'aid cathode and said collector electrode, a concentric line having an inner and outer conductor connected between said cathode and control electrode, and a cavity resonator positioned between said control electrode and said collector, an adjustable coaxial transmission line coupled between said coaxial line and said cavity resonator and including an elognated tubular structure having a longitudinally extending partition providing a pair of adjacent passageways opening into each other at one end, an inner conducting member supported within each of said passageways and an adjustable member connecting the ends of said inner conducting members to change the length of said transmission line, and a coupling loop connected to one end of said transmission line and within said cavity resonator, and a capacity coupling element connected to the other end of said transmission line and extending within the concentric line and coupled to the inner conductor of the concentric line.

9. An electron discharge device having means including a cathode for supplying a beam of electrons, a collector electrode oppositely disposed to said electron supplying means for receiving said electrons, means between said electron supplying means and said collector electrode for modulating said beam of electrons, a first means for applying a radio frequency voltage between said beam supplying means and said modulating means to provide spaced groups of electrons, a first means in the path of said electrons for applying a voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last electrons of each group are accelerated to the greatest extent whereby said groups of electrons are compressed, a second means positioned between said last means and said collector for extracting energy from said compressed groups of electrons, means including a transmission line connected between the means for extracting energy from the comfor modulating said beam of electrons, a coaxial line coupled between said cathode and said grid for applying a radio frequency voltage to said grid to provide spaced groups of electrons, and a collector electrode in the path of the electrons for receiving said electrons, means including a first resonator surrounding the path of the beamof electrons for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last of the electrons of each group of electrons are accelerated to the greatest extent whereby said groups of electrons are compressed, a second resonator between the first resonator and collector for inductively extracting energy from the compressed-groups of electrons, and means coupling said second resonator and said coaxial line.

11. An electron discharge device having means including a cathode for supplying a beam of electrons, a collector electrode in the path of the electrons for receiving said electrons, control means between said cathode and said collector electrode for modulating said beam of electrons, and means including a coaxial line for applying a radio frequency voltage between said cathode and said control means to provide spaced groups of electrons, means including a first resonator surrounding the beam path for applying a variable voltage phased with respect to said electrons for continuously and variably accelerating each group of electrons such that the last electrons of each group areeaccelerated to the greatest extent, means in the path of said electrons for supplying a field-free space through which said groups of'electro-ns are directed and in which compression of each group of electrons occurs, and means including a second resonator between said last means and said collector electrode for extracting energy from said compressed groups of electrons, means including a transmission line connected between the second resonator and said coaxial line for transferring energy to said coaxial line, and another transmission line connected between said second resonator and the first resonator for transferring energy to said first resonator.

12. An electron discharge device having means including a cathode for supplying a beam of electrons, a control grid adjacent said cathode and a collector electrode in the path of said electrons for receiving said electrons, a coaxial line having inner and outer conductors, the inner conductor being coupled to said cathode and the router conductor to said grid for applying voltage to said grid for supplying spaced groups of electrons, means including a first resonator surrounding the path of electrons for applying a variable voltage phased with respect to said electrons for continuously and variably accelerating each group of electrons, such that the last of the electrons of each group of electrons are accelerated to the greatest extent whereby said groups of electrons are compressed, a second res- .pling said second 11 onator positioned between said first resonator and collector for inductively abstracting energy from the compressed groups of electrons, and means coupling said second resonator and said coaxial line, including a coaxial line.

13. An electron discharge device having means 7 including a cathode for supplying a beam of electrons, a control grid. adjacent said cathode for modulating said beam of electrons, and a collector electrode in the path of said electrons for receiving said electrons, a coaxial line coupled between said cathode and grid for applying a radio frequency voltage to said grid to provide spaced groups of electrons means including a first resonator surrounding the path of the beam of electrons for applying a variable voltage phased with respect to said electrons for continuously variably accelerating each group of electrons such that the last of the electrons of each group of electrons are accelerated to the greatest extent whereby said groups of electrons are compressed, a second resonator connected between the first resonator and collector electrode for inductively extracting energy from the compressed groups of electrons, and means couresonator and said coaxial line, and a second coaxial line coupled to said grid, and a coaxial transmission line connected between said resonators.

14. An electron discharge device having means including a cathode for supplying a beam of electrons, a control grid adjacent said cathode for modulating said beam of electrons, a coaxial line coupled between said cathode and said grid for applying a radio frequency voltage to said grid to provide spaced groups of electrons, and a collector elect-rode in the path of said electrons for receiving said electrons, means including a first resonator surrounding the path of the beam of electrons for applying a variable voltage phased with respect to said electrons for continuously and variably accelerating each group of electrons such that the last of the electrons of each group of electrons are accelerated to the greatest extent whereby said groups of electrons are compressed,

a second resonator connected between the first resonator and collector electrode for inductively extracting energy from the compressed groups of electrons, and means coupling said second resonator and said coaxial line, said firstresonator having a movable wall for tuning said first resonator.

15. An electron discharge device having 'an elongated envelope containing at one end a cathode and grid and at the other end a collector electrode, said grid being between said cathode and said collector electrode, a screen and accelerating electrode adjacent said grid, a first resonator surrounding the path of the beam of electrons from the cathode to the collector electrode and positioned between said accelerating electrode and collector electrode, a second resonator surrounding said envelope and coupled between the first resonator and said grid and including a tubular member, a longitudinally movable disc for closing one end of said tubular member whereby said second resonator may be tuned, and a cavity resonator coupled between said cathode and said grid and an adjustable transmission line coupled between said first resonator and the cavity resonator coupled between said cathode and said grid.

ANDREW V. HAEFF.

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

UNITED STATES PATENTS Number Name Date 2,225,447 Haefi et a1 Dec. 17, 1940 2,250,511 Varian et a1. July '29, 1941 2,284,751 Linder June 2, 1942 2,282,295 Hansell May 5, 1942 2,304,186 Litton Dec. 8, 1942 2,314,794 Linder Mar. 23, 1943 2,311,520 Clifford Feb. 16, 1943

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