Optimum design of a matching network for TE11-mode coaxial waveguide horns

The paper deals with the design of an irises matching network in coaxial waveguide. The design procedure allows to get the optimum solution without any iterative experimental analysis. The accuracy and the reliability of the procedure arise from: the complete knowledge of the coaxial horn mismatch, the synthesis method of the network and the electrical characterization of each element of the network. The reflection coefficient of the coaxial horn has been measured in both amplitude and phase by means of a proper gate of the overall feed response analyzed in the time domain. The synthesis procedure of a broad-band matching network takes into account the effect of the interaction between the irides due to evanescent high order modes of the coaxial wave-guide. The single element of the network has been characterized with respect to an arbitrary modal incidence in the coaxial waveguide, also taking into account its finite thickness. The computed and measured results in the frequency band of 4.1-5.1 GHz show that a matchi ng network consisting of three thick irises, placed on the inner conductor of the coaxial waveguide, allows an improvement of the horn return loss from values around 11 dB to values below 24 dB in a 23% frequency band. The results presented have been obtained in the frame of the optimization of the multifrequency feed for QUASAT satellite (+).