Electronically Tunable Half-Mode Substrate-Integrated Waveguide Coupler

This paper presents the design and implementation of a compact and highly efficient –10 dB directional coupler based on a half-mode substrate integrated waveguide cavity resonator configuration. The proposed structure is based on stub-loaded cavity resonators that are responsible for coupling the desired energy to the auxiliary port. A four-resonator arrangement is used to realize the desired coupling level of –10 dB while maintaining compact dimensions. Experimental validation demonstrates a reflection coefficient better than –15 dB, insertion loss below 1.56 dB, and isolation exceeding 15 dB across the operational bandwidth 4.341-5.26 GHz (≈919 MHz bandwidth). Furthermore, a 90-degree phase difference between the through and coupled ports is maintained. The coupler also exhibits tunable coupling characteristics at the coupled port, with experimentally verified coupling levels ranging from 5 dB to 10 dB, highlighting its reconfigurability for adaptive microwave applications.