Super-Compact Substrate Integrated Waveguide Cruciform Directional Coupler

A super-compact substrate integrated waveguide (SIW) directional coupler is proposed and demonstrated. This coupler consists of a simple cross-over of two SIW sections with two inductive metallic posts in a square junction, showing a cruciform. Attractive features including compact size and planar form make this coupler structure easily integrable in microwave and millimeter-wave planar circuits, especially in beam-forming networks. A 3-dB coupler operating at 24GHz is designed using HFSS, fabricated and measured. Characteristics of 15dB isolation and 90deg phase shift between the output and coupled ports are achieved over 18% bandwidth. Design considerations and simulated as well as measured results are presented and discussed.