A Simple Model for Anisotropic Loading of a Vane-Loaded Helix for Broad-Band Travelling-Wave Tubes

Abstract

A simple model is developed for the analysis of a broadband slow-wave structure, for a travelling-wave tube, consisting of a helix supported by a dielectric in a metal envelope provided with metal vanes. Simplified models such as one in which the vanes are replaced by an axially conducting cylindrical sheath at the vane tips and the other in which the vanes are azimuthally smoothed out have been tried out, but with limited success. The combination of the results on the dispersion of the structures obtained using the first of these models with those obtained elsewhere by a rigorous field analysis, considering the angular harmonic effects of the vanes, both the results being interpreted in the framework of equivalent circuit analysis, however, proved to be fairly successful, as evidenced by the validation of the approach against the rigorous field theory.