On one approach to creation of dual-band hard horn

A circular waveguide with longitudinally corrugated wall, in which the grooves are filled with dielectric of alternating epsilon, is considered. The dispersion equation for determining the eigenmode parameters is derived under the assumption of small corrugation period. The waveguide is shown to support the quasi-TEM modes at two different frequencies corresponding to the groove filling at which the hard wall condition is realized. The features of the TEM mode fields are revealed and discussed from the viewpoint of creation of the dual-band hard horn.