Resonant Metasurface Antennas With Resonant Apertures: Characteristic Mode Analysis and Dual-Polarized Broadband Low-Profile Design

Abstract

Resonant metasurface (MTS) antennas (RMAs) are antennas leveraging unusual standing-wave modes of truncated MTS. By introducing resonant exciters, such as wire (electric currents), aperture (magnetic currents), or both, the antenna bandwidth can be improved. However, the contributing modes of apertures are not well recognized. A systematic framework is formulated for the characteristic mode analysis (CMA) and design of RMAs involving resonant apertures, by designing a low-profile wideband dual-polarized RMAs fed by slot arrays at 5 GHz Wi-Fi bands. Unlike regular microstrip patches, the aperture-backed MTS supports two fundamental TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">03</sub> modes of different symmetries. Even and odd symmetries are also observed for the aperture modes. By calculating the radiating power of individual mode, quantitative evidence is provided to clarify the operating principle of RMAs with resonant apertures that the bandwidth improvement and high-isolations are due to the modes from both the MTS and the aperture, rather than from individual. The overall size of the proposed antenna is λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ×λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ×0.058λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ( λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> is the free-space wavelength at 4.8 GHz). The measured bandwidth is 25% (4.8-6.2 GHz) with |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB, |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> | <; -34 dB, boresight gain of 8-10 dBi and cross-polarization level better than -28 dB.