Evaluation of pierce’s small-signal parameters of helix travelling-wave tubes for gain calculation

Abstract

The slow-wave structure of a travelling-wave tube (TWT), consisting of a helix supported by a number of dielectric rods in a glass tube envelope, is modelled and theoretically analysed for the attenuation constant, phase propagation constant and interaction impedance of the structure. The expressions for these quantities are then interpreted to obtain the expressions for Pierce’s velocity, loss and space-charge parameters in terms of the structure parameters. Also, the use of these expressions is demonstrated by a small-signal gain calculation for a typical satellite communication helix TWT in use. The theoretical gain is compared with the experimental gain reported elsewhere, for the same tube. © 1992 IOP Publishing Ltd.