Analysis of Circular-Polarized Full-Duplex Antenna with Sequentially Rotated Array

Patch antennas with sequentially rotated array have been widely used for in-band full-duplex applications by exciting a co-CP (circular-polarized) mode or a dual-CP mode. In co-CP mode, both transmitter (Tx) and receiver (Rx) will have a Tx-to-Rx isolation perfectly and naturally. However, it is hard to be used in some scenarios, such as radar systems, which ask for a dual-CP mode antenna. Theoretical analysis shows that the Tx-to-Rx coupling cannot be fully offset in the dual-CP mode antenna. To solve this problem, a new mode is presented that employs a Tx linear polarization and a Rx circular polarization. A high Tx-to-Rx isolation could be attained. Simulation results show that the antenna provides an Tx-to-Rx isolation lower than -40dB and a realized gain higher than 10 dBi for both Tx and Rx from 5.7 GHz to 5.9 GHz.