Truncated Impedance Sheet Model for Low-Profile Broadband Nonresonant-Cell Metasurface Antennas Using Characteristic Mode Analysis

Abstract

A unit-cell-free truncated impedance sheet model is proposed for the modeling and design of low-profile broadband metasurface antennas (MAs) composed of nonresonant unit cells using characteristic mode analysis. Different from conventional MAs with locally resonant unit cells, the nonresonant unit cells of the proposed MAs only contribute to the grid impedance and the MA operates with the global resonances of the metasurfaces. New measures are also reported to incorporate a higher order metasurface mode for wideband radiation. A low-profile broadband MA is designed at the 5 GHz Wi-Fi bands for the proof of concept. Three modes are excited simultaneously, including a quasi-TM01 mode, a quasi-TM21 mode, and a dipole mode. With a size of $0.8\lambda _{L} \times 0.8\lambda _{L} \times 0.087\lambda _{L}$ ( $\lambda _{\mathbf {L}}$ is the wavelength in free space at the lowest operating frequency), the prototyped MA achieves a bandwidth of 45% with $\vert S_{11}\vert dB, boresight gain of 8.5–11.6 dBi, and 3 dB beamwidth of 40°–60°/43°–65° for the E-/H-planes.