Patent GB-792836-A (GB)
Title: Improvements in or relating to millimetre wave generators using reflex klystrons
IPC: H01J25/24
Filed: 1955-05-17
Abstract: 792,836. Velocity-modulated tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. May 17, 1955 [May 18, 1954], No. 14273/55. Class 39(1). A reflex klyston for generating millimetre waves is provided with a deformable cavity of the rhumbatron type dimensioned to resonate both on a fundamental frequency corresponding to a wavelength of the antimetre band and harmonics corresponding to wavelengths of the millimetre band, said cavity being provided with an output for the fundamental frequency and with one or more outputs for the harmonics, which latter outputs are dimensioned to cut off the fundamental frequency and harmonics of a lower order than 10. The tube shown comprises an electron gun having a cathode 6, heated by a filament 7, and an anode 8 disposed in a cylindrical metal envelope 1 closed at one end by a glass member 2 and at the other end by a hollow truncated metal cone 3 and a metal ring 40. The filament 7 is connected to a battery 9 and the anode 8 is connected to a potentiometer 11 connected across a battery 10. A cavity resonator 41 is bounded by the conical element 3, a flat metal member 4 and a deformable metal wall 5. A reflector 19 is supported by a metal rod 42 inside a cylindrical metal envelope 17 fixed to the member 4 and closed at its upper end by a glass member 18. The reflector 19 is connected to a potentiometer 21 connected across a battery 20. The distance between the openings 13 and 15 in the resonator is adjustable by a mechanism of known type comprising a housing 22, fixed to the envelope 1 by a plate 23, enclosing a ring 24 provided with external teeth and an internal screw thread and rotatable between ball bearings 25. The internal screw thread meshes with a ring 26 rigid with the envelope 17 and the external teeth engage a worm gear 27. On rotating the latter the ring 24 rotates and the elements 17 and 4 unitary with the ring 26 move while the elements 1 and 3 remain stationary Two coils 38 provide a weak axial magnetic field H. The opening 13 is provided with two groups of four radial fins 14 and 14<SP>1</SP> having dimensions #1/2 and #2/2 respectively of the order of 1 mm. A wave trap 33 is provided in the inner wall of the cone 3 to reflect the harmonics. The opening 15, which is preferably of slightly greater diameter than the opening 13 has two groups of four fins 16 and 16<SP>1</SP> (seen from below in Fig. 2 which is a section along the line C-D of Fig. 1; Fig. 1 being a section along the line AOB of Fig. 2.) the dimensions again being substantially #1/2 and #2/2. The resonator 41 is provided with five microwave outputs. Output 30, which is dimensioned to transmit the fundamental frequency centred on a wavelenth #0 in free space, is a coaxial antenna terminating in a loop 39 and loaded by an adjustable impedance 34 through a matching device 35 adjusted so that the load impedance is a practically pure reactance. Two pairs of output waveguides 28 and 29 are dimensioned for transmitting two ranges of wavelengths both shorter than #0/10 and respectively centred on #2 and #1. Each guide is closed by a thin glass window 36. Useful energy in the range #1 is obtained from one guide 29, the other guides terminating in short-circuit pistons 37. The tube may be adjusted to operate on the wavelength #2 in which case both guides 29 would be closed and energy obtained from one of the guides 28.