US2593433A - Ultrahigh-frequency oscillation generator - Google Patents

Description

April 22, 1952 J; H. FREMLIN ET AL ULTRAHIGH-FREQUENCY OSCILLATIONGENERATOR 3 Sheets-Sheet 1 Filed Sept. 9, 1942 J. H. FREMLIN ET AL ULTRAHIGH- Filed Sept. 9, 1942 April 22, 1952 FREQUENCY OSCILLATION GENERATOR 3 Sheets-Sheet B JO/mfis/M W Mm A tlorney April 22, 1952 J. H. FREMLIN ET AL 2,593,433

ULTRAHIGH-FREQUENCY OSCILLATION GENERATOR Filed S t 9; 1942 5 Sheets-Shae: 5

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Attorney Patented Apr. 22, 1952 ULTRAHIGH-FREQUENCY OSCILLATION GENERATOR John Heaver Fremlin and John Foster, London, England, assignors, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application September 9, 1942, Serial No. 457,789 In Great Britain September 19, 1941 12 Claims.

The present invention relates to electron discharge devices, and particularly to ultra high frequency oscillators, of the velocity modulation type. Such devices may comprise one or more resonant cavities or chambers bounded by conducting walls, each provided with a gap leading to the chamber, an electron stream being directed past said gap or gaps in succession so that either the electrons are velocity modulated by the electric field across the gap or energy is abstracted by the field from the velocity modulated electrons passing the gap. At the first gap the electrons are velocity modulated by the electric field across this gap, then they traverse the distance between the two gaps during which they are shielded from the electric field and bunching of the electrons takes place according to known laws. The bunched beam then passes the second gap and gives up high frequency energy to the oscillating field across this gap.

One of the difiiculties in the design of oscillators of the kind referred to is due to the fact that for a system, comprising the tworesonant chambers and connecting electron path, of given shape, whilst the losses increase as ,f f being the frequency of oscillation, the electron beam area diminishes as F. These factors limit both the power output and the highest frequency obtainable.

One object of the present invention is to eliminate this disadvantage and according to the invention the oscillating system is so shaped that the Wavelength of the oscillations generated thereby is independent of at least one dimension of the system. This dimension is preferably substantially perpendicular to the direction of motion of the electrons in the beam. It is easy to show that, apart from a small correction term, the losses are proportional to f and. the beam area is proportional to f Hence whilst in the previous case the current density in the just-oscillating condition is proportional to f, in the resonator according to the invention it is still proportional to f.

In an ultra-high frequency oscillator according to the invention, it is therefore possible to vary said dimension without varying the wave length of the generated oscillation, and at the same time to vary the power output of the oscillator by increasing the electron beam area. It is a further object of this invention to provide a constructional form of resonant chamber system which lends itself to the easy adjustment of the power output.

9 .It is a further object of this invention to pro vide a constructional form of resonant chamber system which lends itself to mass production methods and in which component parts of standard sizes may be combined together to produce easily and quickly a chamber system-in which at least one dimension may be easily adjusted with a view to obtaining an increased power output at a givenfrequency.

According to another aspect of the invention the method of constructing the resonant chamber structure in or for an ultra. high frequency electron discharge device comprises stacking up a plurality of metallic sheets whose planes are parallel to the lines of high frequency current flow and which have apertures corresponding to the desired cross-section or cross-sections of the resonant chamber or chambers and slots correponding to the necessary gaps.

According to another aspect of the invention, in an ultra-high-frequency electron discharge device of the velocity modulation type the resonant chamber structure is constituted .by a stack of plates.

According to another aspect of the invention in an ultra-high frequency electron discharge device of the velocity modulation type, the resonant chamber structure is built up from a plurality of like apertured plates.

The invention will be better understood from the following'description taken in conjunction with the accompanying drawings in which:

Figure 1 shows a perspective view of the resonant chamber system according to the invention; a

Figure 2 shows in perspective view constructional form; 3

Figure 3 is a side view of the form shown in Figure 2; I t

Figure l is a side view of the system mounted in a support; f

Figure 5 is a sectional plan View of the con.- struction shown in Figure 4;

Figure 6 isan exploded view of part of the construction shown in Figure 2;

Figure 7 is a side view of another construction of resonator according. to the invention;

Figure 8 is a plan view of the construction shown in Figure 7, and

, Figure ,9 is an exploded view of part of the construction shown in Figures. '7 and 8.

Figuresloand 11 are two views at right angles of a complete device embodying the invention. Referring now .to Figure 1, four resonant chambers are shown ascylindrical bores in asolictmass of ':metal, ioninstance .of copper. The ibores are a preferred arranged in pairs, la, lb and 2a, 2b, one bore of each pair being on either side of a narrow channel 3 along which an electron beam is directed. Each resonant chamber or bore is provided with a longitudinal slit or opening as indicated at l8 and 19 which connects the chamber with the channel or beam gap 3.

The electron beam producing means and the electron collecting electrodes are omitted from the drawing. In this form of construction, the dimension [3 of which the oscillation generated is independent is the longitudinal length indicated by [3 in the drawing. This resonator is placed in a tube with end plates placed at equal distances from the upper and lower surfaces.

In operation, the electrons first pass the gap I8, the modulating gap, when the beam is velocity modulated, absorbing a negligible amount of energy from the high frequency field across the gap. The electrons then traverse the space between l8 and IS in which they are shielded from :the high frequency field and the beam is bunched according to known laws. The bunched beam then crosses the gap Hi, the working gap, and gives up energy to the high frequency field across the gap.

' The resonant circuits comprising the chambers are closely coupled without the introduction of any special coupling devices and oscillation of nearly the same amplitude and of the same or opposite phase in the modulating ciruits la,

lb," and the energy extracting circuits 2a, 2b can be maintained by the beam. There are a series of discrete beam velocities for which a maximum occurs in the high frequency energy transferred from the beam, giving a series of possible operating voltages.

It will be observed that a resonator of the type described possesses the advantage that there is no interruption or possible faulty connection in the path of the high frequency currents where the intensity is high.

In the embodiment of the invention described the resonant wave length is, neglecting end effects, fixed only by the cross section of the resonant chamber which may be any other shape than circular.

The construction shown in Figure 1 is not easy to construct, owing to the difliculty of lining up the cathode when the slot or beam gap 3 along which the beam travels has a very small depth, I *5 (Fig. 1). It is essential that'the depth of this beam gap be not too great, owing to the reduced efliciency which would result from any large penetrationof high frequency field along the path of the beam. This is particularly important if it is desired that the system should operate at a low voltage. At, for example, 400 volts, it is desirable that the beam gap depth I5 should not exceed 0.015 of the operating wavelength. At 3 cm. wave-length this is only 0.045 cm.

Figures 2 to 6 show a form of construction of the embodiment shown in Figure 1 which overcomes this difiiculty and at the same time makes it possible to use an appreciably increased current and makes manufacture quicker and easier. Figures 2 to 5 show the form of a resonator which has been successfully operated at 3.16, cm. wavelength. The depth of the beam gap 3 is increased over that allowable in the structure shown in Figure 1 and the correspondingly increased penetration of the oscillatory field which would occur, is prevented by the introduction of metal strips 4 arrangedacross thegap andspaced'along the width 14 (Figure4) of 'thebeam gap. 'If the width of the beam gap, is 0.2 cm., the thickness of the metal strips is 0.40 mm., and these strips form a grid across the beam gap as is clearly seen at 4 in Figures 3 and 4. The direction of the beam is indicated by the arrows ll shown in Figure 5. The electron gun is shown diagrammatically at It and the collecting electrode at H.

In order to enable the insertion of the strips 4 the resonator structure is compiled from thin metal sheets stacked one upon the other.

The exploded view of Figure 6 showing only three sheet elements of the structure, indicates how the structure is built up from sections such as 5, 6, 1 of metal sheet. For instance, sections 5 and I, which may be of copper but preferably of molybdenum, or other high heat resisting metal to obtain a greater loading than with copper, provide the metal strips 4 shown in Figure 4. The section 6 which may be of copper or of molybdenum, for example, when temperature considerations must be taken into account comprises two distinct similar parts showing a space between them equal to the beam gap depth of Fig. 4. These sections of metal sheet may be readily punched out in large numbers and assembled to form a structure of any desired length according to the power which is desired. When the sheets have been assembled, they are held in alignment by means of a frame or tubular member 8 into which they may be slid, and are capped at top and bottom of the pile by means of thicker end plates, forexample of copper, 9, l0, as shown in Figure 4 so as to terminate the beam gap width. Apertures [2 are provided in each sheet and cap for the insertion of bolts or rivets for clamping the sheets together. The whole of the stack or only the part relevant to the electron beam is inserted in an evacuated envelope. It will be seen that the advantage mentioned in relation to the structure shown in Figure 1, namely, that there are no interruptions in the high frequency circuit where the high frequency current is high, is maintained in this construction shown in Figures 2 to 6.

This mode of construction is also applicable to similar structures for operating with longer wavelengths, for example, in the region of 5 to 40 cm. or even longer, making it possible to use very much lower voltages with higher currents to deliver a larger amount of power than the oscillators using resonators constructed from one solid mass as shown in Figure 1. Figures 7, 8 and 9 show another form of construction, in which the same references are used as in Figures 4, 5 and 6 to designate like parts. It is not considered that any further description of these figures is necessary.

The electron discharge device shown in Figures 10 and 111s an ultra high frequency oscillation generator adapted to feed electromagnetic waves into a wave guide by means of a rod antenna 24 secured in electrical contact to the top plate 9 of the stack of plates forming the resonating cavity system, at an antinodal point. The part embodying'the present invention is the stack of rectangular plates designated 20 and the associated electron beam producing means. This stack 20 and the end member 9 sandwich between them a mica plate 30 of annular formation and a metallic plate similarly apertured to the other plates, but of smaller exterior dimensions is inserted in the aperture in mica plate 30 so as to maintain the metallic and electrical continuity of the stack and top plate 9. A further mica plate 29 is provided at the bottom of the-stack 20, and

between the mica plates 29 and 30 are mounted in position the electrodes for producing the beam of'electrons. The cathode and control grid are shown at I6 and the anode at 3| with a collecting electrode I! behind the anode. The electrode I1 is primarily of experimental value as an oscillation detector and the anode 3| has an aperture to allow some of the electrons to pass through to the collector electrode ll, the presence of oscillations being shown in a circuit connected to H.

The plates of the stack are held together by bolts which pass through apertures such as, l2 shown in Figures 2, 5 and 6. The Whole structure is mounted on the base of a U-shaped member 28 through which pass two bolts which are secured by means of nuts 21. Th member 28 is then secured to two supporting pillars secured in the press of the glass envelope 25.

For a fuller description of this device shown in Figures and 11 reference may be made to the specification of co-pending application of J. H. Fremlin and C. H. Foulkes, Serial No. 476,465, filed February 19, 1943, and now U. S. Patent No. 2,476,971.

Frequency variation can be obtained by the interposition of dielectric or conducting rods into the oscillatory circuit or by other known means suitable to tubes in which the oscillatory circuit is in an evacuated bulb.

Whilst the resonant chambers have been shown as of circular cross section, they may of course be of any desired shape, for example, rectangular or elliptical.

It will also be understood that the invention is not limited to resonators formed in a solid mass, but they may equally well be made up from bent ,metal sheet. It will also be understood that the method of construction described is also applicable to single chamber systems, for example as incorporated in an electron velocity modulated discharge device of the reflected beam type, or to systems having more than two resonant chambers.

What is claimed is.

1. An ultra high frequency electron discharge device comprising a cavity resonator including a stack of like apertured conducting plates, means forming an electron path through said resonator parallel to the planes of said plates and transversely of the depth of said stack, and certain of said conducting plates being slotted for coupling the cavities of said resonator to the electron beam.

2. An utra high frequency electron discharge device comprising a cavity resonator block having cavities of uniform cross sections along their respective linear longitudinal axes and gaps connecting said cavities with a linear beam gap in said block, said block comprising a stack of thin metal stampings having apertures corresponding to the cross sections of the resonant cavities and having slots corresponding to said gaps, and means at one end of said beam gap for producing a beam of electrons and for directing said beam along said beam gap.

3. An ultra high frequency electron discharge device comprising a plurality of stacked conducting plates, each having a plurality of apertures in alignment and slots connecting said apertures to an outside edge of said plates at spaced points, said plates being stacked with the corresponding apertures of said plates in alignment and the corresponding slots in alignment, and means aligned with said points for producing a beam of electrons along a path parallel with saidedge 6 and for directing said beam past the slots of a plate in succession.

4. An ultra high frequency electron discharge device according to claim 3, comprising further 5 conducting plates of high heat resistance having like apertures to those in the first mentioned plates, said further plates being interleaved between said first mentioned plates in the stack with their apertures in alignment with the apertures in said first mentioned plates, said further plates having portions extending into said path of said electron beam.

5. An ultra high frequency electron discharge device comprising a pair of stacks of conducting plates each plate having a plurality of apertures and slots connecting said apertures to an outside edge of said plate, the plates in each stack being stacked with corresponding apertures of said plates in alignment and the corresponding slots in alignment, means retaining the two stacks in fixed relative positions with corresponding slots {directly opposite each other and with a space between said stacks forming a beam gap, and means-aligned with said beam gap for producing a beam of electrons and for directing said beam along said beam gap plates.

6. An ultra high frequency electron discharge device according to claim 5 comprising further conducting plates of high heat resistance having apertures corresponding to those in the first mentioned conducting plates, and having slots connecting a pair of apertures in said further conducting plates corresponding to a pair of apertures on opposite sides of said beam gap and immediately opposite each other, said further plates being interleaved between the conducting plates of the said two stacks with their apertures in alignment with corresponding apertures in said stacks and said further plates having portions extending across said beam gap.

7. An ultra high frequency electron discharge device comprising two stacks of like apertured conducting plates with a beam gap therebetween for the passage of an electron beam, the apertures in said plates forming cavities of uniform cross section along the depths of the stacks and said plates having longitudinal slots connecting the said cavities with the beam gap, further conducting plates of high heat resistance interleaved with the plates of said two stacks and extending across said beam gap, said further plates having apertures corresponding ,to said cavities and having slots connecting pairs of apertures on opposite sides of said beam gap.

55 8. An ultra high frequency electron discharge device according to claim 7 further comprising Q; thicker plates at the top and bottom of said two stacks of plates and like apertured to said further conducting plates defining a greater depth of said cavities.

9. An ultra high frequency electron discharge device comprising a laminated resonator block, .the laminae of the block comprising thin metal plates having at least one round hole and a com- 65 municating narrow slot formed therein, the

laminae being stacked with the holes and slots in registry to define a cylindrical bore and an elongated narrow cavity extending longitudinally of the block. 70 10. An electron discharge device comprising a laminated resonator block, the laminae of the resonator block comprising a plurality of thin sheet metal discs, the discs each having a round ,hole, and a communicating narrow slot, the holes 'l' 'izand slots being in registry in the stack of discs defining a cylindrical bore and an elongated narrow cavity extending longitudinally of the block, said narrow cavity being extended to open through a wall surface of said block outside of said bore in the form of an elongated narrow slot in said wall surface, and means forming an electron path transversely across said narrow slot substantially throughout the length thereof and in a direction substantially parallel with the planes of said discs.

11. An electron discharge device comprising a source of electrons, a laminated block adjacent said source of electrons, said block comprising a series of stacked laminae, each lamina having a space in which electrons may flow from said source, and a space forming a cavity resonator connected to said first space.

12. An electron discharge device comprising a laminated resonator block, the laminae of the resonator block comprising a plurality of thin sheet metal discs, the discs each having a round hole, and a communicating narrow slot, the holes and slots being in registry in the stack of discs defining a cylindrical bore and an elongated narrow cavity extending longitudinally of the block, said narrow cavity being extended to open through a wallsurface of said block outside of said bore in the form of an elongated narrow slot in said wall surface, an electron emitting element positioned between the end planes of said resonator block, and means including anode JOHN BEAVER. FREMLIN. JOHN FOSTER.

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

UNITED STATES PATENTS Number Name Date 342,553 Westinghouse May 25, 1886 1,661,830 Hull Mar. 6, 1928 1,684,947 Daumann Sept. 18, 1928 2,043,733 Brasch et al June 9, 1936 2,044,413 Weyrlch June 16, 1936 2,063,342 Samuel Dec. 8, 1936 2,157,952 Dallenbach May 9, 1939 2,193,600 Mouromtseil et al. Mar. 12, 1940 2,202,380 Hollrnann May 28, 1940 2,209,923 Kilgore July 30, 1940 2,270,777 Von Baeyer Jan. 20, 1942 2,289,984 Mouromtsefi et a1. July 14, 1942 FOREIGN PATENTS Number Country Date 215,600 Switzerland Oct. 16, 1941

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