Mode-matching modeling of a hard conical quasi-TEM horn realized by an EBG structure with strips and vias

A conical horn with hard wall used for supporting the quasi-TEM-mode having a uniform field distribution over the cross section is modeled. The hard wall is realized as an electromagnetic bandgap (EBG) structure using a dielectric layer loaded with narrow longitudinal strips connected to the basic metallic wall by radial vias to prevent excitation of the strip-line mode. The modeling is based on a stepwise approximation of the horn surfaces by a set of cylindrical sections. Each section consists of a strip-loaded part and a longitudinally corrugated part representing the vias. The stepped horn characteristics are calculated by using the mode-matching method combined with the Winer-Hopf-Weinstein method for accurate account of the wave scattering at the aperture. The strip-line mode resonance effects are studied and demonstrated. It is shown that if the length of the strip part of each section sufficiently differs from the resonance value, the performance of the hard strip-loaded horn with vias is similar to high performance of the appropriate hard corrugated horn. Recommendations are given on appropriate choice of the maximum spacing between the vias providing the absence of resonance effects in the specified frequency band.