Metasurface-Inspired Wideband Circularly Polarized Antenna Array in Ka-Band Using Characteristic Mode Analysis

This letter proposes a wideband metasurface (MTS) inspired circularly polarized (CP) antenna array working in the Ka-band, which consists of 2 × 2 antenna subarrays fed by a sequential-rotation (SR) network. The MTS radiator consisting of a 2 × 2 rectangular patch with a cross patch embedded in the center is applied to contribute two CP modes for wideband operation with the help of characteristic mode analysis. An I-shaped slot located on the ground plane is employed as the coupling excitation for the CP radiation. To further enhance CP bandwidth, MTS-antennas sequentially rotated by 90° are incorporated with the SR network, which outputs uniform orthogonal phased signals. To verify the proposed design, several prototypes are fabricated and measured. The results show an impedance bandwidth of 25–37.2 GHz (39.35%) and 25–38.05 GHz (41.4%) for 4 × 4 and 8 × 8 arrays, respectively, while a 3 dB axial ratio bandwidth of 26.5–35.5 GHz (29%) and 26.5–34.5 GHz (26.3%) are realized. The peak gain of 17.51 and 20.82 dBic are achieved in the vicinity of 30 GHz.