Wide-Bandgap All-Metal Mushroom Unit Cells with Air Gap Shifting and Stress Mitigation for 30 GHz Gap Waveguide Applications

This paper introduces two novel all-metal mushroom-type unit cell designs for groove gap waveguide (GGW) and ridge gap waveguide (RGW) applications in millimeter-wave (mm-Wave) and sub-mm Wave systems. Building upon the conventional All-Metal Mushroom Unit Cell (AL-MUC), the proposed designs present two significant novelties, one as an air gap shifting technique to enhance electromagnetic confinement, and second, structural modifications to mitigate stress concentration at sharp edges, thereby improving mechanical robustness. The proposed approaches enable the unit cells to achieve wide bandgap characteristics, including wider stopband bandwidth and lower insertion losses, while maintaining compatibility with cost-effective fabrication methods (e.g., milling for air-gap-shifted designs and 3D printing for stress-optimized structures). The designs are optimized for the 30 GHz mm-Wave band and demonstrate better performance compared to existing literature, as validated through full-wave electromagnetic simulations. The results show the proposed unit cells as promising candidates for future gap waveguide systems in high-frequency communication networks, radar, and mm-wave applications.