GB677536A - Improvements in thermionic valves for ultra-short waves - Google Patents

Abstract

677,536. High-frequency discharge apparatus. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. July 20, 1949 [July 20, 1948], No. 19160/49. Class 39 (i). An electron beam tube comprising two parallel conductors 1, 2 between which an electrostatic field is established and wherein a constant magnetic field is applied perpendicular to the electric field and the direction of propagation of the beam, the two conductors constituting a retardation line in which is excited an electromagnetic wave whose speed of propagation is substantially the same as the speed of the beam, whereby the wave is amplified by interaction with the beam, is characterized in that a plurality ot cathodes 8 are distributed along the retardation line at intervals whereby the beam of each subsequent cathode interacts with the wave when the amplification due to the interaction of the beam of the previous cathode no longer increases sufficiently; preferably the distances between successive cathodes diminish from the input to the output end of the tube. In. Fig. 1 the conductor 1 is provided with a plurality of pins 3 to slow down the wave and the line is tapered at each end to match it to the input and output which may be capacitative connections to the Lecher lines 12. The cathodes 8 are in the plane of conductor 2 which may be at cathode potential but is preferably negative with respect to the cathodes. The magnetic field is perpendicular to the plane of the drawing. In the tube shown in cross-section in Fig. 4 the conductor 1 is a flattened helix connected at each end to a coaxial line 15; the cathodes 8 are arranged between the helix 1 and the planar conductor 2. Conductors 1 and 2 are fixed in ceramic members 14 which may be of aluminium or beryllium oxide. At the end of the line a copper block is provided to collect the electrons and it may be cooled with water or compressed air. The electromagnetic wave may be partly reflected at the cathodes 8 and to correct this obstacles which are preferably in the form of fins 22, Fig. 5, may be arranged in front of the cathodes which may be provided with focusing electrodes 23. The lower conductor 2 may be provided with fins 3 to assist in slowing down the wave, Fig. 6 (not shown). The Specification as open to inspection under Sect. 91, comprises also tubes with a single cathode and a tube using an electron gun to fire a beam down the delay line. In Fig. 10 (Cancelled), the upper conductor 1 comprises a metal sheet bent so that the medial portion supports the retarding fins 3 whilst the spaces between the fins are coupled to one another by the capacitors 24, 25 formed by the ends of the fins and a fold of the metal sheet; the thickness of this capacitative portion may be varied by compression and the phase velocity of the wave can thus be varied. Arrangements in which the spacing, dimensions, and contour of the fins are varied at each end of the line for matching purposes are also described. This subject-matter does not appear in the Specification as accepted.