Design of single-layer broadband omnidirectional metasurface antenna under single mode resonance

A single-layer broadband vertically polarized (VP) omnidirectional metasurface antenna is proposed in this communication. To guide the optimization and design of the antenna, characteristic mode (CM) analysis (CMA) is performed to investigate the intrinsic modal behaviors of the metasurface. A mode with VP omnidirectional radiation is first identified by analyzing an array of 4 \times 4 squared patches. To excite this mode, a complex feeding network is required, which leads to gain loss and increased structural complexity. Furthermore, the mode currents change with the frequency. Consequently, this mode cannot be excited efficiently in a wide bandwidth using a fixed feeding structure. To solve these problems, the modal current is analyzed at different frequencies. The sizes of the four corner patches and the other four edge patches are adjusted to optimize the modal behaviors. After optimization, the mode becomes much more desirable and can be efficiently excited in a wide bandwidth using a single probe. Therefore, the proposed antenna can be designed on a single-layer substrate and excited by a simple feeding structure with broadband characteristics. To verify the design, the proposed metasurface antenna is simulated, fabricated, and evaluated. The results show that the proposed metasurface antenna can achieve a broad bandwidth of 64.2%.