Substrate integrated waveguide 180-degree narrow-wall directional coupler

Substrate integrated waveguide (SIW) is a new type of guided wave structure which could be implemented in both microwave- and millimeter wave integrated circuits. The study combines narrow-wall directional coupler with slow wave structure in SIW technique and achieved an over 5.4% bandwidth with ±0.3dB power equality, -20 dB isolation and 180 degrees phase shift between the output- and coupled ports as well for a coupler of length of 0.59. Its low cost and small size make it attractive for many narrowband applications.