Design and optimization of a compact Ka-band antenna diplexer

A computer code based on the mode matching method has been developed to analyze diplexer structures. A new design of very compact broadband low-loss diplexer for a satellite antenna in the Ka-band is presented. The main components of the developed diplexer are: an asymmetrical E-plane bifurcation that plays the role of a power divider, a low-pass corrugated waveguide filter in the TX port, and an inhomogeneous transformer to match the RX port. Two consecutive optimization processes have been carried out. First, each of the three components of the diplexer is optimized. Secondly, optimization of the whole structure, including all the discontinuities and the higher order modes interactions, leads to the optimized diplexer. Numerical and experimental results for the optimized Ka-band diplexer are presented. A very good performance of the diplexer and an excellent agreement between computations and measurements are observed from these results. Measured insertion losses lower than 0.2 dB over both frequency bands (TX-RX) are obtained.