US3475645A

US3475645A - Gap tuned reflex klystron having an enlarged movable diaphragm disposed in r.f. isolation with respect to the r.f. cavity

Info

Publication number: US3475645A
Application number: US616752A
Authority: US
Inventors: Curtis E Ward
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1967-02-08
Filing date: 1967-02-08
Publication date: 1969-10-28
Anticipated expiration: 1986-10-28

Description

Oct. 28. 1969 c. E. WARD 3,475,645 GAP TUNED REFLEX KLYSTRON HAVING AN ENLARGED MOVABLE DIAPH M DISPOSED IN ELF. ISOLATION WITH RESPECT To THE Rd. CAVI Filed Feb. 8, 1967 2| 2o 22 24 o o FREQUENCY (cc) I l 7 v INVENTOR.

6 CURTIS E. WARD United States Patent U.S. Cl. 3155.22 2 Claims ABSTRACT OF THE DISCLOSURE An improved gap tuned reflex klystron is achieved for operation in the millimeter wavelength portion of the R.F. spectrum. At frequencies e.g., in the -70 gHz. region, the R.F. cavity dimensions become extremenly minute and attempts to design gap tuned reflex klystrons with flexible diaphragms forming a wall portion of the R.F. cavity present diflicult fabrication problems as well as diaphragm life problems. By introducing an R.F. choke section around the reflector electrode and positioning the flexible tuning diaphragm external to the R.F. cavity it is possible to eliminate fabrication and diaphragm life problems since the diaphragm size is no longer dependent upon the operating wavelength of the tube.

Typical prior art reflex klystrons having a gap tuning design and representative of prior art deficiencies which the subject invention overcomes are found in U.S. Patent No. 2,825,842 by D. E. Kenyon. U.S. Patent No. 2,521,719 by L. R. Hildebrand; U.S. Patent No. 2,593,443 by A. E. Harrison, U.S. Patent No. 2,837,685 by G. C. Dalman.

Brief summary of the invention The reflex klystron is a well known and highly advanced electromagnetic wave generator which has found extensive applications in the microwave spectrum. Since the design principles are well known to those skilled in the art reference to any of innumerable reference sources including patents can be made for further information. The present invention represents an improvement in gap tuned reflex klystrons which facilitates the manufacture and use of tubes in the millimeter wave spectrum. Prior art gap tuned klystrons, see the above-cited patents, present fabrication problems in the millimeter wave spectrum due to the minute dimensions of the R.F. circuitry involved at such frequencies. A gap tuned tube using a flexible diaphragm as a part of the R.F. cavity is no longer really feasible due to diaphragm life problems. Even apertured diaphragms which do not form a part of the vacuum envelope but function as R.F. walls will crack and permit R.F. leakage and thus introduce loss and undesired spurious resonant conditions. If the teachings of the present invention are followed such problems are in general obviated. By introducing an R.F. choke section around the reflector electrode and disposing the movable diaphragm which supports the reflector end wall portion of the R.F. cavity externally of the R.F. circuit fabrication problems are eliminated since the size of the movable diaphragm is no longer dependent upon cavity size, Thus in essence by forming a portion of the tube vacuum envelope with a movable diaphragm which is in R.F. isolation with respect to the R.F. cavity an improved tunable reflex klystron results.

It is therefore a primary object of the presentinvention to provide an improved gap tuned reflex klystron.

Brief description of the drawings FIG. 1 depicts a fragmentary cross-sectional view;

"ice

partly in elevation, of a reflex klystron incorporating the teachings of the present invention.

FIG. 2 is a side view taken along the lines 22 in the direction of the arrows.

FIG. 3 is a plan view of FIG. 1 taken along the lines 33 in the direction of the arrows with one side partially broken away.

FIG. 4 is an illustrative graphical portrayal of power out and gap spacing vs. operating frequency for a reflex klystron such as depicted in FIG. 1.

Detailed description Turning now to FIG. 1 there is shown a reflex klystron 5 having any conventional electron gun means 6 disposed at the upstream end portion of an enlarged portion of bore 29 in solid metal block 7 as of copper which forms the device main body. The gun 6 or electron beam generating and focusing means can be of any conventional type well known in the art. For example a thermionic heater 8 can supply heat to a dispenser cathode region 9 which in conjunction with the application of a suitable DC. potential diflference between focusing electrode 10 and main accelerating anode portion 11 will induce formation of an electron beam in a manner well known in the art. A pair of grids 12, 13 are disposed at the one end of anode header 11 having a central beam aperture 14 and at the end of a reflector sleeve 15 from an interaction gap 16 for re-entrant resonant cavity 17 in a manner well known in the art. The electron beam is bunched and caused to return to the gap region 16 by a reflector electrode 18 forming a portion of reflector means 19 having a suitable negative potential applied thereto relative to anode potential in a manner well known in the art. Electromagnetic wave energy at the operating frequency is extracted via iris 20 and wave permeable vacuum tight window 21 and output waveguide 22 to be used for any purpose dictated by the user, e.g. laboratory signal generator.

Since it is imperative that the R.F. cavity and beam path regions be evacuated to pressures such as 10- torr and lower, vacuum integrity is a necessary condition for tube operability. Since the tube is to be gap tunable, that is the resonant frequency of operation will be variable by control of gap spacing 16 to capacitively vary the L-C circuit formed by gap 16 and cavity walls formed by the block 7 and header-grids 12, 13 a means for completing the vacuum envelope must be included. However, the reflector 18 must be maintained in DC. isolation with respect to the anode-body also and means for eliminating R.F. leakage from the cavity must be included also. As discussed previously, these requirements are extremely difficult to realizein millimeter wave tubes by the use of a simple flexible diaphragm forming a portion of the R.F. cavity wall due to fabrication and diaphragm stress and fracture problems. The solution presented by the present invention involves the use of R.F. isolation means 24 between the R.F. cavity 17 and the flexible vacuum Wall or diaphragm 25. This permits the use of a flexible diaphragm which has greatly enlarged dimensions relative to the R.F. cavity dimensions and is not subject to failure or fabrication problems. The diaphragm 25 can be made out of any suitable material such as Monel and has its interior edge brazed or the like to a reflector support shell 27 and its exterior edge brazed or the like to a flanged portion in the main body block 7 as shown. An alumina or other suitable dielectric ring 28 is used to support the reflector electrode 18 in DC. isolation with respect to the other portions of the tube and maintain vacuum integrity. Conventional metal to metal and metalceramic bonding techniques can be used for all joints and conventional materials can be used for tube parts.

The gap spacing 16 is varied via movement of support plate 30 which supports the reflector assembly and interior edge of the movable diaphragm as shown best in FIGS. 2 and 3. An excellent, rigid yet movable support technique for plate is the use of a pair of semirigid yet bendable support pins or

posts

31, 32 as of copper, stainless steel disposed in a pair of bores 33, 34 in the plate 30 and tube main body and fastened therein by pressure fit, screw thread, braze etc. The central portion 35 of the yieldable support posts 31, 32 is preferably of reduced cross-section to provide the desired flexibility. The opposite end of plate 30 is provided with an aperture 37 and the opposing main body portion with a threaded aperture 38. A bolt 39 and spring washer 40 complete the tuning design. By simple rotation of bolt 39 the plate 30 is moved towards or away from the main body block 7 and the reflector end header-grid 13 is similarly moved to control gap spacing 16 and thus the operating frequency. The support plate thus forms a lever arm which is pivotable by simple rotation of bolt 39 which in turn causes the plate 30 to move the header 13 via the reflector sleeve 15 disposed in a central bore 29 in main body block 7.

The R.F. isolation means 24 includes a pair of folded one-quarter wavelength choke sections 40, 41. By making the first annular choke length between A and B a quarter of an electrical wavelength long at the center of the tube operating band and by making the choke region between B-C the same, the short at C is reflected to A and R.F. energy is precluded from entering this region. A second folded choke 40 doubles the effectiveness of the design by providing the same R.F. short to any R.F. leakage through the first choke section. Thus D.C. isolation between tube body-anode 7, 11 and the deflector electrode 18 is maintained between a pair of

smooth surfaces

18, 15 and reflector-anode voltages of better than 1000 volt differential are easily accommodated without breakdown in a compact arrangement, and R.F. isolation to the flexible vacuum diaphragm 25 is assured without prior art danger of cracking of the diaphragm and consequent R.F. leakage. Even if the prior art R.F. diaphragm did not form a portion of the vacuum envelope R.F. leakage would induce spurious resonances and consequent noise problems if fracture of the diaphragm occurred in use.

A reflex klystron tunable between 20-24 gHz. as shown in FIG. 4 using the design described above was built and successfully tested with a power output spectrum as shown in FIG. 4 and R.F. gap spacing variations as also shown in FIG. 4. The device used a one-inch diameter diaphragm 25 and an R.F. cavity of 0.214 inch diameter. No interfering modes were encountered indicating the effectiveness of the R.F. choke sections. The R.F. power spectrum was comparable to a fixed tuned tube which indicates the losses introduced by the chokes at the ends of the tunable band are minor. Since the diameter of the diaphragm 25 which forms a portion of the vacuum envelope is independent of the operating frequency the design can be easily scaled in frequency up into the upper gHz. region without loss of tuning life.

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. In a high frequency electron discharge device of the reflex klystron type including electron beam forming and projecting means disposed at the upstream end portion of the device, reflector means disposed at the downstream end portion of the device and beam wave resonant cavity means disposed therebetween to form a vacuum envelope for said device, the improvement comprising a portion of the vacuum envelope of said device having flexible wall means disposed about the reflector means in DC. isolation with respect to the reflector electrode and including means for maintaining said flexible wall means in R.F. isolation with respect to said resonant cavity means, said reflector means including a reflector header forming a portion of a re-entrant interaction gap portion of said resonant cavity means, said reflector header being supported by a header support sleeve coaxially disposed about said reflector electrode and having its downstream end portion coupled to said flexible wall means, said means for maintaining said flexible wall means in R.F. isolation with respect to said resonant cavity means including R.F. choke means coaxially disposed about said reflector header support sleeve and means for varying the gap spacing of said re-entrant interaction gap portion of said resonant cavity means.

2. The device defined in claim 1 wherein said means for varying the gap spacing of said re-entrant interaction gap portion of said resonant cavity means includes a re flector means support plate forming a pivotable lever arm, said support plate being mounted on said device and pivotable via yieldable support pins in one end portion thereof and a rotatable support bolt means on an opposing end portion thereof.

References Cited UNITED STATES PATENTS 2,651,738 9/1953 Ebers 3155.21 2,843,794 7/1958 Hergenrother 315--5.22 2,866,123 12/1958 McCann 315-522 2,966,611 12/1960 Sandstrom 315-5.22

HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, JR., Assistant Examiner US. Cl. X.R. 331-84