GB689588A - Travelling-wave tube with an output cavity resonator and with a drift space - Google Patents

Abstract

689,588. Travelling-wave tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. June 27, 1950 [July 12, 1949], No. 16024/50. Class 39(i). A travelling-wave tube amplifier comprises an input retardation line in the form of a helix 4, in which the incoming wave is amplified by interaction with the electron beam while the latter is modulated in velocity and in density, an output cavity resonator 8 excited by the density modulated electron beam, and a drift space between the line and the resonator in which there is no interaction between the beam and the wave. The line is terminated in an attenuation element 6 of such form as to dissipate the amplified incoming wave without giving rise to reflections. The drift space l is preferably of a length equal to a coefficient comprised between 1 and 1.5, divided by the value of the real part of the wave propagation constant of the line. The bunching of the electrons in the drift space may be enhanced by inserting a detuned cavity resonator coupled neither with a generator nor with a load circuit in the drift space. The bunching may be still further increased by so dimensioning the retardation line that the coupling between the wave and the beam is of the same order of magnitude for the fundamental frequency as for the second harmonic. The attenuation element may be replaced by an output circuit so as to utilize the amplified input wave. The final collector electrode, or the collector electrode and the output resonator are preferably at low potentials with respect to the line so as to minimise energy loss due to dissipation of heat at the collector, but sufficient to ensure collection of all the electrons. The retardation line may be a helix as shown, or a multi-vane or perforated-disc waveguide for example. Specification 660,792 is referred to.