GB702145A - Improvements in or relating to transverse electron-discharge travelling-wave tubes - Google Patents

Abstract

702,145. Velocity modulated tubes. LELAND STANFORD JUNIOR UNIVERSITY, BOARD OF TRUSTEES OF. Oct. 27, 1950 [Oct. 27, 1949], No. 26279/50. Class 39(1) A reflex velocity modulated tube has a hollow pipe waveguide 3, Fig. 1, with conductive walls and input and output connections for a travelling wave, a strip cathode 19 and accelerating and focusing electrodes 17, 25 arranged at one side of the guide for projecting a sheet beam of electrons across the guide, and a reflecting electrode 27 at the other side of the guide. The cathode 19 is indirectly heated, focusing electrode 25 is connected to the cathode and the guide has electron permeable grids 9, 15. The guide 3 is sealed through the metal envelope via insulating seals 39 and an exhaust pip 37 is arranged at one of the end walls of the envelope. Alternatively the envelope may be of glass as indicated in Fig. 4 (not shown). The spent electrons are collected by the re-entrant guide walls 11 and by other conductive parts. The device will amplify in both directions and this makes it necessary to provide a good impedance match between the ends of the guide 3 and the input and load devices to avoid setting up oscillations. Amplification will occur over a number of discrete frequency bands corresponding to electron transit times between traversals of the guide of one, two, three or any other small number of cycles so that impedance matching over all possible frequencies is difficult. The device may be modified to amplify in one direction only by giving the electrons a component of velocity in the direction of the travelling wave. This may be done by inclining the cathode, focusing and accelerating electrodes with respect to the guide, Fig. 4 (not shown) and/or by providing a transverse magnetic field by means of an electromagnet, Fig. 5 with pole pieces 57, 59. In Fig. 5 the accelerating grid 17<SP>1</SP> is preferably arranged below the level of the lower guide wall and hence below the pole pieces, instead of on the same level as the lower guide wall as in Fig. 1. Specification 701,356, [Group XIV], is referred to.