Bandwidth Enhancement of Low-Profile Metasurface Antenna Using Nonuniform Geometries

Artificial magnetic conductor metasurface antennas are investigated using a robust, surrogateassisted, differential evolution optimization technique. Using a uniform metasurface array configuration as a starting point, multiple array configurations are parameterized and the differential evolution optimizer yields nonuniform array geometries exhibiting wideband performance. The bandwidth improvement is attributed to the structure's ability to support additional higher-order modes with good impedance matching. A comparison between the uniform metasurface antenna cases and their 'evolved' nonuniform counterparts is presented to demonstrate the advantages of the proposed technique. Two prototypes are fabricated and characterized to experimentally confirm the advantages of proposed designs. The first prototype, a 3x3 case, measured a fractional bandwidth of 36.8% with peak gain of 8.3 dBi. The second prototype, a 4x4 case, measured a fractional bandwidth of 51.8% with peak gain of 8.8 dBi. When compared to standard uniform cases, the proposed nonuniform geometries exhibit substantial impedance bandwidth enhancement.