An analysis of broadband corrugated conical horn antennas taking account of space harmonics due to mode converters

Since the mode converter in a corrugated conical horn antenna consists of a nonperiodic structure in which the depth or the width of the corrugated groove changes gradually, unwanted higher order modes can be generated in the case of oversizing. In this paper, non-periodic structure of this type is modeled as a multiple connection of uniform corrugated waveguides. Space harmonics are taken into consideration under the assumption that the number of stages of the corrugated grooves is not too small. A normalization condition for the corrugated mode function is proposed such that the average transmitted power in one period of the corrugated waveguide in a cylindrical region is unity. By means of the mode matching method, the scattering matrix corresponding to these mode functions is derived. Using this process, the scattering matrices are cascaded for each period of the corrugation and the scattering matrix and the radiation pattern for a corrugated conical horn antenna can be obtained. When the measured and computed values of the radiation pattern of the broadband corrugated conical horn antenna are compared, we confirm that agreement is excellent for both the principal polarization and the cross polarization components. Rom the amplitude and phase of the measured radiation pattern, the amount of unwanted higher order modes generated (in both amplitude and phase) is estimated and the validity of the method is verified by comparison with computed values. (C) 1998 Scripta Technica.