An optimised waveguide to microstrip transition at K band

An improved transition from rectangular waveguide to microstrip is presented. This transition consists of a ridge waveguide transformer with the ending step extending over the microstrip and two side grooves which maintain the microstrip in its correct position, ensuring both a good electrical contact without soldering and an optimum measurement repeatability. In addition to step ridges, used for matching purposes, also the main guide is stepped in the wider side in order to obtain a single-mode operation in all sections of the transition. The transition is analysed by a full wave mode-matching method and optimised over the 17.7-19.7 GHz band. Measurements are performed in back-to-back configuration using a TRL calibration and the scattering matrix of a single transition is obtained using a de-embedding technique. Experimental results agree well with theory and measured return loss is better than 28 dB over the 16-20 GHz frequency band.