Propagation and radiation behaviour of corrugated feeds. Part 1: Corrugated-waveguide feed

An investigation of the propagation and radiation behaviour of circular corrugated waveguides is described. Particular attention is given to modes of unity azimuthal dependence because of their importance in antennafeed applications. It is shown that the radiation pattern of a corrugated waveguide exhibits nearly perfect symmetry over a 1.5:1 frequency band, and, when the corrugations are approximately λ/4 deep, the pattern is symmetric and there is no crosspolarised component of radiated field. The attenuation of the dominant HE11 mode is investigated theoretically and is shown to be less than that of the H11mode in a uniform waveguide over at least a 2:1 frequency bandwidth. An important similarity is described between the propagation behaviour of a corrugated waveguide and that of a dielectric rod of low relative permittivity, such as those used in fibre optics and optical waveguides. Finally, the determination of the input voltage standing-wave ratio (v.s.w.r.) at the junction between homogeneous and corrugated waveguides is theoretically and experimentlly studied.