Empirical Formulas for Designing Gap-Waveguide Hybrid Ring Coupler

A new type of hybrid ring coupler (or rat-race coupler) the gap-waveguide ring hybrid has been developed in this work. The advantages of the new gap-waveguide ring hybrid are low manufacturing cost since the good electrical contact between metal plates is not required, and lower transmission loss compared to microstrip line since there is no dielectric material needed. Therefore, the gap-waveguide technology opens up a possibility of waveguide integration circuit from millimeter wave up to terahertz. We present an empirical formula for designing the gap-waveguide ring hybrid based on simulated data and has been verified by measurements of a prototype of the ring hybrid realized at 16 GHz. The prototype has an operating frequency band of 2 GHz around 16 GHz, with a reflection coefficient below -10 dB and a phase difference between two output ports of 182◦ ± 2◦.