US2815467A

US2815467A - High frequency tube

Info

Publication number: US2815467A
Application number: US477157A
Authority: US
Inventors: Bernard C Gardner
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1954-12-23
Filing date: 1954-12-23
Publication date: 1957-12-03
Anticipated expiration: 1974-12-03
Also published as: GB790142A; DE1204335B

Description

Dec. 3, 1957 B. c. GARDNER- 2,815,467 HIGH FREQUENCY TUBE Filed Dec. 23, 1954 5 Sheets-Sheet l saw/11 INVENTOR.

Armeflev B. C. GARDNER HIGH FREQUENCY TUBE Dec. 3, 1957' 3 Sheets-Sheet 2 Filed Dec. 23, 1954 :EIl j a INVENTOR. efierlzard'rgfarai zen .BY

fi/fl 74AM Aria/FIVE? Dec. 3, 1957 B. c. GARDNER 2,315,467

HIGH FREQUENCY TUBE Filed Dec. 25. 1954 5 Sheets-Sheet 3 IN V EN TOR.

ATTORNEY HIGH FREQUENCY TUBE Bernard C. Gardner, Los Altos, Califl, assignor to Varian Associates, San Carlos, Califl, a corporation of California Application December 23, 1954, Serial No. 477,157

.13 Claims. (Cl. 315-5.21)

This invention relates generally to ultrahigh frequency tubes and has reference, more particularly, to novel ultrahigh frequency reflex klystrons.

Ultrahigh frequency reflex klystrons or velocity modulation tubes employing a cavity resonator and electron beam reflector as heretofore constructed have been relatively expensive to produce owing to the use of expensive multiple exacting machine operations necessitating extremely accurate manufacture and assembly.

The principal object of the present invention is to provide a novel reflex klystron tube that is of relatively simple rugged construction and easily fabricated largely of pressed metal parts whereby the overall cost of a tube of this general type is greatly reduced.

Another object of the present invention is to provide a novel reflex klystron that is extremely stable as to frequency and has a long life in use, with low distortion and which is suitable for transmitter-receiver service in microwave relay systems, as a local oscillator, a radio frequency generator as well as for other uses.

Another feature of the present invention is to provide a novel tube of the above character that has an external cavity portion of exceptional frequency stability so that the tube has substantially negligible frequency drift in use, said tube being externally tuned to eliminate complicated tuning structures and being adapted to be mass-produced at minimum cost.

A further feature of the present invention is to provide a novel tube structure comprising component parts which may be fabricated into a series of tubes of differing fre quency ranges without the necessity of changing the dimensions of the parts used.

Other features and advantages of the present invention will become apparent from a perusal of the following specification taken in connection with the following drawings wherein the invention is embodied.

In the drawings,

Fig. 1 is a part longitudinal sectional view of the novelreflex klystronof the present invention,

Fig. 2is a part sectional view taken along lines 2-2 of Fig. 1,

Fig. 3 is a part sectional view taken along lines 3-3 of Fig. 2, and

Fig. 4 is a view similar to Fig. 1 of a somewhat modified structure. i A

Similar characters of reference are used in the above figures to designate corresponding parts;

Referring now to Figs. 1 to 3 of'the drawings, the reference numeral 1 designates a housing or bulb portion of the novel tube of this invention within which the cathode or gun assembly 2 is contained. This cathode assembly has a-cylindrical vitreous sealing base 3 having a flange 18 supportedupon and secured to a ring member 4 that is'braz'ed at 5 to a stepped or flanged portion of the bulb 1. The joint 5 together with the flange 4 and sealing'base 3 serve to seal off the bottom of the bulb 1 so that a vacuum may be maintainedw-ithin this in Rise. A tubebas'e 7' of plasticoi' other suitable insunited States atent lating material having terminals 8 is secured to the outer free end of bulb 1 as by crimping of the material of this bulb into recesses provided in the periphery of tube base 7 as indicated at 9.

The cathode button 10 is shown as of the convex focusing type and is indirectly heated by a heating coil 11 supplied through leads 13 connected to terminals 8. Coil 11 is contained within a cylindrical housing 12 which also carries the button 10, housing 12 in turn being supported by brackets or straps 14 fixed upon the inner wall of a hollow cylindrical support, and heat shield 15 as by spotwelding thereto. Support 15 also serves as a focus electrode for the electron beam emitted from the cathode button 10. This combined focus electrode heat shield and supporting member is formed by die pressingsheet metal and is provided with outwardly struck ears 16 in its lower portion for supporting this member as by spotwelding to the stem wires 17 projecting from the base 3.

A hollow cylindrical anode 20, having a slightly conical or dished washer like anode header 21 assembled thereon as by brazing, is inserted within the bulb 1 concentrically with the cathode button 10 so that the electron beam leaving this button in use passes through the hollow interior of anode 20.

The washer-like anode header 21 surrounds the anode 20 and supports the same upon the inner walls of the bulb 1. In assembling the header 21 upon the anode 20, the former is adjusted longitudinally along the length of the anode 20 as shown by the dot dash lines in Fig. 1 to thereby vary the size of the resonant cavity to suit the frequency range desired. This arrangement allows the use of a fixed length gun assembly 2 for a complete series of tubes of differing specific frequency ranges.

The inner end of the hollow anode 20 is provided with a grid 22 which is somewhat spaced from an opposed grid 23 shown mounted in a ring 24 secured to the inner end 25 of the bulb 1. The inner end 25 of a second bulb 1'- is secured to the end 25 in abutting relation as by brazing. A reflector 26 is positioned opposite the grid 23 and spaced therefrom for reflecting the electrons back into the resonant cavity 27 formed within bulb 1, header 21 and anode 20. The reflector 26 is of substantially cup-shape and is pressed from sheet metal and is provided with an external apron or cylindrical portion 28 which apron extends outwardly and is provided with bent out ears 29 to which supporting stem wires 17 are secured as by spotwelding. The wires 17' are carried by a sealing base 3 similar to base 3 which base is supported by a ring member 4 secured as by brazing 5 to the flange or step portion 6' of bulb 1'. The outer end of the portion 1 is closed by a base or cover 7' similar to the base 7, the cover 7 of plastic or other insulating material being secured to the outer free end of bulb 1 by crimping the material of the bulb into recesses provided in the periphery of the cover 7 as indicated in 9'. An external central conducting stem 30 is providedon the cover 7 and is electrically connected to one of the wires 17' as by lead 31.

Thus it will be seen that the bulbs 1 and 1' together with their cathode and reflector assemblies can be fabricated largely from similar standard pressed metal parts, the stem wires 17 and 1'7 serving to respectively support the cathode assembly and the reflector assembly thereby eliminating special mounting struts for these members. The cathode assembly including the focus electrode 15, the anode 20 and the reflector 26 are all automatically centered so as to be truly concentric during the assembly of the tube. Where it is desired to maintain a fixed reflector voltage for a series of tube types having differing frequency ranges, it is necessary to change the length of the wires 17 somewhat so as to vary the spacing between grid- 23 and reflector 26. However, where a fixed refiector voltage is not necessary the Wires 17' can all be made of the same length for a complete series of tubes of progressively varying operating frequencies. One side of the bulb 1 is pressed in as indicated at 32 making the transverse cross section of the bulb have a D-shape to provide a flat wall portion of appreciable extent so as to accommodate a relatively long and somewhat narrow transverse iris opening 33. By thusly making this opening long and narrow the anode header 21 can be moved up and down within the inner portion of bulb 1 without covering a portion of this iris opening.

Positioned externally of the flat wall 32 is an external resonator portion 54 comprising

sections

34 and 35 having abutting flanges 36 that may be soldered or otherwise secured together. Section 34 is formed with an inner flat end 37 abutting and secured to the flat wall 32. The wall 37 is provided with a window 38 that is aligned with iris opening 33 but is appreciably larger than this opening as illustrated in Figs. 1 and 3. Positioned within the section 34 and in abutting relation to the end wall 37 is shown a plate member 39 having an opening 40 therein that is similar to window 38 but again is larger than this window for receiving a mica closure 41 that is sealed as by glass 42 around its edges to the plate 39. Since opening 40 is a good sized opening it is possible to employ a good sized piece of mica for effecting the closure of the window 38 thus enabling easy assembly of this portion of the tube. Also, since the iris opening 33 is smaller than the window 38, the tendency for sealing glass to overlap the iris opening 33 is substantially eliminated. Hence a sharp clear cut aperture is provided for the passage of energy from within resonator 27 into external resonator portion 54, the latter resonator portion being sealed off from the evacuated inner resonator portion 27. A screw 43, which preferably is inclined, is threaded through the wall of section 34 and is directed toward the window 38 for concentrating the electromagnetic field in the vicinity of this window and enhancing the passage of energy through the window and into the external cavity 54. Once this screw 43 has been adjusted to obtain optimum energy interchange it can be locked in place as by spot welding and the screw slot filled by a sealing composition 44, if desired, to prevent unnecessary tampering with the screw adjustment.

To effect the tuning of the tube without physically distorting the walls thereof which is undesirable since it increases microphonics and increases the possibility of leaks and lowers the tube frequency stability, a tuning screw 45 is employed which is threaded through a block 46 mounted on the section 35, the screw projecting into this section. A leaf spring tension device, comprising a leaf spring lock washer 47, which presses at one side against the block 46 and its other side carries a nut 48 fixed therein and through which the screw 45 is threaded, serves to hold the screw in adjusted position and against turning. Thus, to vary the tuning of the tube it is merely necessary to turn the screw 45, the setting of the screw being retained in fixed position by the spring tension device described.

When it is desired to use the tube of this invention to cover a series of separated frequency ranges use may be made if desired of waveguide ridges 49 shown in full and in dot dash lines in Fig. 1 of the drawings to aid in obtaining the desired frequency range, one of these ridges also being shown in Fig. 3, said ridges having the effect of changing the effective electrical dimensions of the external cavity 54. A mounting flange 50 is shown secured as by brazing to the section 35, the flange 50 being adapted to be connected to a similar flange provided on an input of the equipment to which the tube is connected. In practice it has been found that a considerable series of ranges of operating frequency can be obtained without employing the ridges 49 by merely adjusting the screw 45 and at times varying the size of the output opening in flange 50. The tube is shown provided with cooling fins 51 spaced apart by spacers 52 and mounted upon the reduced portions of bulbs 1 and 1'. These fins and spacers can be slid over the bulb and brazed in place during the assembly of the tube.

In use, the tube has good inherent temperature compensation by virtue of the fact that not only cooling is provided by use of fins '51 together with the use of heat conducting thin pressed metal parts but as the tube heats up in use the tendency of cavity 27 to enlarge and increase in inductance is compensated for by the action of the slightly outwardly dished anode header 21 having a coefficient of thermal expansion larger than the coeflicient of thermal expansion of the cavity side walls. This header as of, for example, copper acts to move the anode 20 downwardly slightly, as viewed in Fig. 1, while the tube body, as of steel, heats up thereby slightly increasing the spacing of grids 22 and 23 and lessening the capacity therebetween and hence compensating for the increased inductance of the resonator, thereby maintaining the operating frequency of the tube substantially constant.

Fig. 4 of the drawings illustrates a structure similar to the preceding figures with the exception that the anode 20 is of such dimensions as to receive the cathode 10 and its focusing electrode 15' therewithin, thereby enabling the cathode to be placed relatively close to the resonator gap and enabling good control of the optics of the tube regardless of the adjustment of the anode header 21' along the exterior surface of the anode 20'. In this form of the invention an accelerating grid 53 is shown carried by the interior wall of anode 20' and positioned opposite the cathode button 10' to aid in focusing the beam through the tube gap. Otherwise this construction is similar to that of the preceding figures.

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

What is claimed is:

1. A high frequency tube comprising two similar bulb members having opposing ends secured together and carrying a first grid, a hollow anode provided within one of said bulb members and having a grid at one end thereof in axial alignment with and opposing said first grid and spaced therefrom, an anode header extending between said anode and the walls of said bulb member, said header being positioned intermediate said grid and the other end of said anode to form a cavity resonator therewithin of dimensions suitable for a selected frequency range, similar cathode and reflector sealing base members carried respectively by said bulb members in axial alignment with said anode, said cathode base member carrying a cathode assembly and said reflector base member carrying a reflector, said cathode assembly serving to direct a beam of electrons through said anode, said resonator and said grids toward said reflector for reflection back into said resonator.

2. A high frequency tube as defined in claim 1 wherein said cavity resonator is provided with a wall portion having a relatively long narrow transverse iris opening therein, whereby said anode header during the fabrication of the tube may be variably positioned longitudinally within said cavity resonator corresponding to differing operating frequencies of said tube without covering said iris opening. 7

3. A high frequency tube as defined in claim 2 wherein said cavity resonator is provided with an external resonator portion having a window opening therein aligned with the iris opening of said resonator, said window opening being appreciably larger than said iris opening, and a sealing closure for said window, said closure serving to seal off the cavity resonator while at the same time permitting the passage of energy therefrom into said external resonator portion.

4. A high frequency tube as defined in claim 3 wherein said external resonator portion is provided with a threaded aperture adjacent said window, and a screw threaded through said aperture and terminating in the vicinity of said window for concentrating the electromagnetic field in the vicinity thereof to enhance the passage of electromagnetic energy therethrough.

5. A high frequency tube as defined in claim 4 wherein said external cavity resonator is provided with an adjustable tuning screw threaded thereinto, and tension means for holding said screw in adjusted position.

6. A high frequency tube comprising opposed similar sheet metal bulbs secured together at their abutting inner ends, said abutting ends being centrally apertured, a grid in said aperture for permitting the passage of an electron beam, the outer ends of said bulbs being formed with outwardly offset portions providing internal seats, a cathode assembly positioned within one of said bulbs for emitting electrons for passage within said bulbs, a reflector assembly positioned within the other of said bulbs for reflecting the electrons back toward said cathode, similar sealing bases for said bulbs having outwardly projecting flange members secured to said seats, said sealing bases respectively supporting said cathode and reflector assemblies in axial alignment within said bulbs.

7. In a thermionic tube, a casing comprising two similar hollow bulb members having inner abutting ends affixed together, similar sealing base members mounted for closing and sealing off the outer portions of saidbulb members, a cathode assembly positioned within the first of said bulb members and carried by its base member, a reflector assembly positioned within a second of said bulb members and carried by its base member and a cavity resonator within said first bulb member, the abutting ends of said bulb members being apertured for receiving an electron beam passing from said cathode assembly through said resonator toward said reflector, and similar base members closing the outer ends of said bulb members.

8. A thermionic tube as defined in claim 7 wherein said cavity resonator is provided with a cylindrical anode surrounding the electron beam and an anode header plate secured to said anode for determining the operating frequency of said tube, said header plate being slightly dished to effect automatic temperature compensation of said tube.

9. A thermionic tube as defined in claim 7 wherein said sealing base members have conducting wire stems extending therethrough, said reflector assembly and said cathode assembly having projecting ears to which said wire stems are attached, to thereby support said assemblies within said tube casing, and from said base members, said base members having outwardly extending ring members secured to said bulb members for positioning said reflector and cathode assemblies axially within said tube.

10. A thermionic tube as defined in claim 7 wherein said cavity resonator is provided with an external resonator portion having a Window opening therein communicating with said cavity, a sealing closure in said window, said closure serving to seal off the cavity resonator while at the same time permitting the passage of energy therefrom into said external resonator portion, and a metallic member carried by said external resonator portion and extending close to said Window for concentrating the electromagnetic field in the vicinity thereof to enhance the passage of electromagnetic energy therethrough for utilization.

11. A high frequency tube comprising a temperature compensated resonant cavity having a re-entrant portion and adapted for electromagnetic interaction with a beam of electrons passable therethrough, said cavity having side Walls and end walls, one end wall being provided with an outwardly dished portion, said outwardly dished cavity end wall having a coeflficient of thermal expansion higher than the coefficient of thermal expan sion of the cavity side walls whereby as the operating temperature of the cavity is increased the gap spacing between the re-entrant portion and an end wall is increased in variable accordance with the temperature to maintain a substantially constant resonant frequency in a fluctuating thermal environment.

12. A high frequency tube body adapted to contain therewithin a cavity resonator for electromagnetic interaction with a beam of electrons passable therethrough comprising two sheet metal bulb members having oppos ing ends coupled together, one of said bulb members having a substantially flat side wall portion providing a transverse cross-section of the tube body with a portion of substantially D-shape to facilitate coupling of said bulb to an external wave propagating structure, said fiat side wall portion of said bulb member having a relatively long and narrow transverse coupling slot therein for providing a wave energy communication path between the relatively shallow cavity resonator contained within the tube body and the external Wave propagating structure.

13. In a high frequency tube apparatus, a cathode assembly for providing a beam of electrons, a cavity resonator adapted for electromagnetic interaction with a beam of electrons passable therethrough, a reflector for returning the beam of electrons through said cavity resonator for successive electromagnetic interaction, said reflector comprising a unitary thin walled tubular member closed off at one end by an inwardly dished transverse wall provided with a hollow rounded peripheral flange, said member having radially projecting ears at the other end thereof for coupling to a plurality of supporting members.

References Cited in the file of this patent UNITED STATES PATENTS 2,490,030 Cooke et a1 Dec. 6, 1949 2,508,346 Lafierty May 16, 1950