A Novel Multifunctional EBG-Based Coupled-Line-Defect Directional Coupler Based on Layered Dielectric Substrates

In this paper, a novel multifunctional coupler based on line-defect layered electromagnetic bandgap (EBG) waveguides is proposed and studied. Extensive full-wave simulations are used to establish the critical nature of the coupling region for the realization of different functionalities of the coupler. Changing the separation between the rings or orientation of the rings in the coupling and/or channel regions leads to very interesting and unique coupling mechanisms, such as forward-wave, through-wave, and/or backward-wave quasi-0- and 3-dB couplers that distinguish the proposed topology from conventional proximity directional couplers. In the final analysis, one can switch between configurations by changing the orientation of the rings in the coupling region. These configurations with coplanar-slot-line feeding structures are fabricated and tested at X-band for demonstration purposes. Measurement results validated the design procedure and confirmed the general trends in simulations. The proposed EBG coupler is promising for beamforming matrix and antenna array feeding networks.