A Wideband Spherical Fabry–Perot Cavity Antenna Based on Positive Phase Gradient Metasurface

Expanding the bandwidth of resonator cavity antennas (RCAs) is challenging, and most studies have focused on using positive phase gradient partially reflective surfaces (PRSs). Although multilayer PRSs can provide bandwidth enhancement, they have the weaknesses of extremely high design complexity and thresholds in bandwidth improvement. Here, a new approach is proposed to significantly enhance the 3-dB gain bandwidth of the RCA while maintaining high gain and low profile. The method begins by utilizing an open resonator with a spherically modified ground (SMG) to activate multiple resonances akin to Laguerre–Gaussian beam modes. Positive phase gradients are then added to the frequency band between each resonant mode for phase optimization, all provided by a simple metasurface. The proposed approach has been verified across multiple designs and the antenna prototype of one design has been selected for fabrication. The measurements agree very well with simulations, showing a 3-dB gain bandwidth of about 40%, a peak gain of 19 dBi, and a sidelobe level of around −10 dB. This work demonstrates a new low-profile, high-gain, wideband, low-design complexity antenna for various wireless systems.