Ultrawideband High-Gain Planar Endfire Antenna Utilizing Higher-Order Modes of Spoof Surface Plasmon Polaritons

This letter introduces an ultrawideband high-gain planar endfire antenna utilizing the first four higher-order modes of spoof surface plasmon polariton (SSPP). By adjusting the width of the four interdigital branches near the opening of the meandered slot SSPP unit, bandgaps between the higher-order modes were eliminated without increasing size, facilitating ultrawideband performance, which is a key innovation of this work. A flare slot was formed by linearly increasing the gap between two SSPP transmission lines, effectively reducing antenna sidelobes. Additionally, a metamaterial array with flower-shaped units was designed to enhance gain. A prototype was fabricated, showing measured and simulated impedance bandwidths of 113.5% from 13.8 GHz to 50 GHz, with peak gains of 20.3 dBi and 20.6 dBi, respectively. The results are in good agreement.