A Wideband Omnidirectional Metasurface Antenna Using Characteristic Mode Analysis

A wideband omnidirectional metasurface antenna has been proposed. The characteristic mode analysis (CMA) was applied to explore the modal behaviors of the metasurface and guide the design. The proposed metasurface is designed based on a 5 x 5 square patched array, which is a hybrid metasurface incorporating square patches with 2 x 2 and 3 x 3 subarrays in a distributive arrangement, significantly improving the bandwidth and current distribution over a wide band. By properly adjusting the sizes of these elements, the bandwidth and gain are further improved. Based on the predicted excitation of the metasurface, a probe center-fed circular patch is introduced on the bottom layer, which not only excites the metasurface but also generates an additional mode to compensate the metasurface for attaining stable omnidirectional radiation. An antenna prototype was simulated, fabricated, and tested. The results show that the proposed antenna achieves a wide bandwidth of 70.1%, a peak gain ranging from 2 dBi to 6 dBi, and radiates a good omnidirectional pattern.