3 dB 90$^{\circ}$ Hybrid Quasi-Optical Coupler With Air Field Slab in SIW Technology

This letter presents a new class of small-size and high performance directional coupler based on substrate integrated waveguide (SIW) technology. This type of coupler is composed of a waveguide section of four arms connected by a central junction. Quasi-optical coupler technique is realized on standard waveguide by simply inserting a slab with different permittivity in central section to act as a mirror. To make this coupler realizable in the SIW format, the air slab is simply implemented by rectangular through-hole. Characteristics of the proposed coupler with respect to various parameters are presented and discussed. A prototype at 10 GHz is designed, fabricated and measured. Experimental results show that the proposed SIW cruciform coupler has a bandwidth of more than 15% over the operating frequency range.