Wideband High-Gain Polarimetric Metasurface-Integrated Antenna at Higher-Order Modes

A substrate-integrated waveguide (SIW)-based wideband and high-gain polarimetric metasurface integrated antenna is proposed in this paper for millimeter-wave (MMW) applications. The antenna operates on higher-order modes (TE130/TE310 and TE230/TE320) to achieve wide impedance bandwidth and enhanced gain. The radiation characteristics are shaped using strategically positioned slots with unequal spacing to suppress broadside nulls and control side lobe levels within a single-element structure. Characteristic Mode Analysis (CMA) identifies the modes and their coupling behavior, guiding further bandwidth and gain enhancement through effective mode combination. A dual-polarized metasurface composed of plus-shaped unit cells provides broadband reactive loading and polarization symmetry, improving radiation uniformity without increasing the design complexity. The fabricated prototype achieves a bandwidth of 20.2% operating within the frequency range from 24.9 to 30.5 GHz with isolation of 26 dB, a peak gain of 12.5 dBi, and stable co- and cross-polarized radiation across the band. The proposed dual-polarized antenna–metasurface configuration offers an efficient solution for advanced MMW applications requiring broadband, high-gain, and polarization-stable performance.