Extremely wideband ridge gap waveguide-based 3-dB coupler using supershaped coupling apertures

This paper introduces a novel broadband 3-dB coupler based on ridge gap waveguide (RGW) technology designed using supershapes to achieve exceptional bandwidth while maintaining a compact footprint. By leveraging the superformula-a parametric model capable of generating complex geometries with minimal computational effort-the proposed design enables efficient exploration of a wide design space. Furthermore, to ensure efficient excitation of the coupler across the entire operational bandwidth two novel transitions from RGW to coaxial line and double-ridge waveguide are designed. The proposed coupler achieves a fractional bandwidth of 75.8% over the 18-40 GHz range (covering both K and Ka bands), featuring a return loss better than 18 dB, a coupling level of 3 ± 0.3 dB, isolation exceeding 22 dB, and a significantly compact footprint of 0.8λg-substantially smaller than conventional designs. Simulation and measurement results confirm the effectiveness of the proposed approach, demonstrating its suitability for high-performance broadband applications in microwave and millimeter-wave (mmWave) systems.