Metasurface Antenna With Cocircularly Polarized Radiation Characteristics for Wideband Monostatic Simultaneous Transmit and Receive Applications

A monostatic simultaneous transmit and receive (STAR) antenna system consisting of a metasurface-based STAR antenna and two elaborately designed microstrip-based feeding networks is proposed to suppress the self-interference (SI) from transmission (TX) to reception (RX), a key challenge in STAR design to realize its potential in doubling system capacity. The metasurface antenna is for the first time used in designing a monostatic STAR antenna system for its compact and wideband characteristics. The proposed STAR antenna system possesses the features of monostatic operation, wide bandwidth, high TX/RX isolation, cocircularly polarized radiation with similar patterns for TX and RX, easy fabrication, and low cost. The metasurface-based STAR antenna is formed by four dual-polarized metasurface antennas, or units, and is used for both TX and RX to achieve monostatic operation. A wide operating bandwidth is obtained for each antenna unit by combining the resonate modes of the unit and a crossed slot, the feeding structure of the unit, using characteristic mode analysis (CMA). To achieve high TX/RX isolation and identical right-handed circular polarization (RHCP), the four TX and RX ports of the STAR antenna, respectively, are excited with equal amplitudes and relative phases of 0°, 90°, 180°, and 270°, by two dedicated-designed wideband feeding networks based on the sensitivity analysis. Accordingly, the proposed STAR antenna system is prototyped. The measurement results show that the STAR antenna system achieves $>$ 36 dB TX/RX isolation and <3 dB axial ratio from 4.5 to 6 GHz and maintains similar radiation patterns with the same RHCP for TX and RX.