Design of H-plane waveguide cruciform hybrid using dielectric posts

A compact H-plane waveguide cruciform coupler using metallic posts has recently been proposed. It consists of two rectangular waveguides crossing each other at right-angles, two metallic posts arranged on a diagonal line of the cross region for producing directional properties, and one metallic post inserted for matching at each waveguide port. Generally, it is known that any lossless reciprocal 4-port circuit with two-fold symmetry can constitute 90-degree directional coupler, if the four ports are completely matched. In this work, a design of the cruciform hybrid coupler using dielectric posts instead of metallic posts is attempted [3]. The analysis and the design are performed based on the H-plane planar circuit approach for short-circuited boundary segments with the use of the segmentation method. It is shown that good frequency characteristics with fractional bandwidths of about 10% can be realized for the X-band waveguides. The validity of the design results is confirmed by an EM-simulator (Ansoft HFSS) and an experiment.