Air-to-Dielectric-Filled Two-Hole Substrate-Integrated Waveguide Directional Coupler

A two-hole directional coupler consisting of an air-filled substrate-integrated waveguide (AFSIW) coupled to a dielectric-filled substrate-integrated waveguide (SIW) is introduced and studied for the first time. The design of the proposed two-hole coupler, based on different dielectric-loaded SIWs and on multilayer printed circuit board process, is presented in detail with its theoretical foundation. The proposed coupler is of interest for monitoring high-performance, self-packaged, and low-cost millimeter-wave substrate integrated systems based on AFSIW. For demonstration purposes, a forward coupler operating in the Ka-band satellite uplink frequency band (27 to 31 GHz) has been designed and fabricated. In its frequency range of operation, it achieves measured insertion loss, coupling, and isolation of 0.28 ± 0.15 dB, 20.8 ± 0.24 dB, and 46.76 ± 3.92 dB, respectively.