A Compact, Monostatic, Co-Circularly Polarized Simultaneous Transmit and Receive (STAR) Antenna With High Isolation

A compact, high-isolation, monostatic, co-circularly polarized (CP) simultaneous transmit and receive (STAR) antenna with similar radiation patterns is presented. The proposed antenna system consists of a sequentially rotated array (SRA) of four dual-polarized antenna elements and two quadrature feeding networks. The four transmit (TX)/receive (RX) ports of the STAR antennas are fed with equal amplitude and relative phase values of 0°, –90°, –180°, and –270° to generate identical right-handed CP for both TX and RX channels. The array element spacing to maximize the radiation performance of the STAR antenna is investigated. Two feeding networks with low phase and amplitude errors are designed based on the sensitivity analysis of the TX/RX isolation to realize high TX/RX isolation. The whole antenna system is integrated into one radio frequency (RF) front-end module using multilayer printed circuit board (PCB) technology. The proposed antenna has a compact size of 122.36 mm (1
λ
₀
) × 122.36 mm (1
λ
₀
) × 4 mm (0.03
λ
₀
), and exhibits more than 40.6 dB TX/RX isolation and better than 1.1 dB axial ratio (AR) over the 2.4–2.5 GHz band in the measurements.