Waveguide Filter Integrated into a Planar Circuit

Design and results of a waveguide filter are presented. The filter is integrated into the carrier block of a planar microstrip circuit. The coupling from the planar microstrip circuit to the waveguide filter is achieved via slots in the ground plane; these coupling structures, at the same time, act as first and last inverter of the filter. The remaining inverters and all filter resonators are realized using reduced height metal waveguide. In this way, low loss of waveguide resonators is combined with planar circuits and a compact setup.