Low-profile Directional Coupler Based on Staggered Mushroom-Like Double-Layer Gap Waveguide

In this paper, a 3-dB directional coupler based on the staggered mushroom-like double-layer gap waveguide (SMDGW) transmission line with low insertion loss and low profile is presented. It consists of two hollowed substrates, two metal plates and three stacked substrates. Two pairs of metallic vias and a slot located in the mushroom-like electromagnetic bandgap (EBG) structure are designed to achieve the coupling between the two transmission lines, and the magnitude can be achieved by changing the number and distance of the vias. The simulated results show that the proposed coupler achieves a bandwidth of 19.9% ranging from 24.4 to 29.8 GHz, a profile of 0.22λ, a power equality of 3.45 ± 0.15 dB and an isolation of 18 dB.