Design of Integrated Substrate Gap Waveguide 3-dB Rectangular-Junction Couplers

A 3-dB rectangular-junction directional coupler is designed using integrated substrate gap waveguide (ISGW) technology. The coupler uses the odd mode and even mode of Q-TEM to phase difference of 90°. The proposed coupler has a coupling ratio of
$3.8\pm 0.5\text{dB}$
, a phase deviation within 2.5° around 90°, above 20dB isolation and return loss from 27.8GHz to 33.2GHz centered at 30GHz.