Ten-Mode Single-Fed Low-Profile Wideband Circularly Polarized Metasurface Antenna Using Dual-Mode Aperture-Coupled Higher Order Modes

The bandwidth of low-profile circularly-polarized (CP) metasurface (MTS) antennas is often limited in the upper band margin due to gain degradation and distorted patterns resulting from insufficient number of functional modes. In this paper, a ten-mode low-profile aperture-fed wideband CP MTS antenna is proposed. Different from conventional triple-mode designs using the 1st-order slot-mode and the TM10/01 MTS modes, seven additional higher-order modes (HOMs) are incorporated for improved gain and pattern symmetry in the upper-band margin for bandwidth enhancement. The seven new modes include the 3rd-order slot-mode, four TM12/21/30/03 MTS modes and two newly-found TM1.5,1 and even-TM12 MTS modes, all of broadside radiation. The inter-mode phase difference for CP radiation is achieved by mode manipulation with four loadings combined, including surface capacitive loading, corner truncation, diagonal via-loading and Z-slot loading. With an overall size of 0.86λL × 0.86λL × 0.057λL at the lowest frequency, the proposed ten-mode MTS antenna achieves a measured bandwidth of 40.5% (4.68–7.06 GHz) with axial-ratio (AR) < 3 dB, |S11| < –10 dB, gain of 6.9–8.5 dBic, symmetric patterns and significantly lower upper-band gain drop < 0.5 dB.