GB699631A - Improvements in or relating to ultra high frequency electrical amplifiers and oscillators - Google Patents

Abstract

699,631. Velocity modulated tubes. MULLARD RADIO VALVE CO., Ltd., and KNOTT, G. March 31, 1950 [April 1, 1949], No. 8913/49. Class 39(i) [Also in Group XL(b)] An amplifier or oscillator comprises a hollow rectangular waveguide 1, Fig. 1, within which is arranged a stack of parallel conductive rectangular plates 2 lying at right angles to the electric field component of an H mode electromagnetic wave in the guide, the plates being secured directly to the guide at two opposite lateral edges to divide it into parallel slots, and an aperture 4 through the stack of plates through which an electron beam passes. The arrangement is such that electrons are cumulatively accelerated or decelerated at the gaps between the plates and are shielded from alternate half cycles of the input wave entering the left hand guide portion by the plates, so as to produce velocity modulation and bunching of the beam. The bunched beam generates an amplified output wave in the right hand guide portion. The guide may be closed at one or both ends by a conductive member or members so that the device functions as an oscillator with one or two resonant cavities. In a modification, Fig. 2 (not shown), the stack of plates taper away from the gun in progressively increasing and decreasing senses at the input and output sections of the guide respectively. This is stated to improve the impedance matching and to reduce feedback. In another modification, Fig. 3 (not shown), the device effectively comprises two separate guides and stacks of plates, the stacks being placed one on top of the other in registry, and the two guides carrying the input and output waves respectively. In another modification, Fig. 4 (not shown), the output is taken from a cavity resonator arranged at the side of a single stack of plates remote from the gun. In another modification, Fig. 5 (not shown), the guide is closed at both ends. The end closures may be conductive so that the device serves as an oscillator or may be provided with windows so that the device can be inserted in a waveguide system and function as an amplifier. In all forms the output may be increased by employing a plurality of beams co-operating with a similar number of apertures. The aperture or apertures or one or more sets of apertures are located at a position or positions of maximum electric field, e.g. centrally for an H 01 mode and at “, or both “ and ¥, of the width of the guide from one side thereof for an H 02 mode. The plates may be tapered towards both ends thereof in the longitudinal direction of the waveguide so as to improve the impedance matching.