The estimation of radiation losses from a tapered H-guide: application to the analysis of IDG antennas

Tapered inset dielectric guide (IDG) antennas may be analysed by modelling the IDG as an H-guide. This allows a reasonable estimate of the aperture fields to be obtained, from which the far-field radiation pattern of the antenna may be derived. In the past, theoretical methods for the analysis of tapered IDG antennas have included a simple amplitude multiplication factor, determined by trial-and-error; to cater for the effect of mode conversion along the IDG taper. This paper presents a method by which power transfer to other bound modes and to the radiation spectrum may be calculated. This method is based on the variable-bound mode matching approach of Brooke and Kharadly (1982). The new technique allows the unsatisfactory empirical method used previously to be dispensed with. The power loss characteristics identified by this technique provide new insight into the structure, and have implications for future IDG antenna designs. Radiation patterns calculated using results from the bound mode matching method compare well with measured values, and demonstrate improvements upon predictions made by existing techniques.