Dual-Band Dual-Sense High-Gain Circularly Polarized Metasurface Antenna Using Characteristic Mode Analysis

A novel dual-band dual-sense circularly polarized (CP) metasurface (MTS) antenna with high-gain performance is designed. A 2 x 3 square patch array, as the basic MTS, is investigated at first. We observe that besides the two fundamental modes with desired broadside patterns, the basic MTS also possesses two higher order modes with high-level sidelobes. The sidelobes are yielded by the reverse currents on the middle patches of the MTS, which can be canceled by modifying the middle patches into poor radiators. Then, two coupled-fed slots are employed to excite two fundamental modes and two higher order modes of the modified MTS. Moreover, the fields of the four orthogonal broadside modes are adjusted to meet the magnitude and phase requirements of the CP wave. All the mentioned processes are under the guidance of the characteristic mode analysis. Finally, the proposed MTS antenna is fabricated and measured. The measured results agree well with the simulations, showing 3 dB axial ratio bandwidths of 4.37-4.45 and 6.03-6.24 GHz with CP waves in different handedness. The measured peak gains in the lower and higher bands are 10.22 and 10.72 dBic, respectively.