Compact Microwave FMCW Radar Using Circularly Polarized TX/RX Antennas

In this paper, a compact microwave FMCW radar using circularly polarized transmitting (TX) and receiving (RX) antennas is presented. Both TX and RX antennas are triangular patch antennas with circular polarization. The TX and RX antennas are placed complementally along the diagonal of a rectangular surface. Such arrangement brings special compactness. In addition, TX antenna is left-hand circularly polarized (LHCP), while RX antenna is right-hand circularly polarized (RHCP). The combination of LHCP and RHCP significantly enhances the polarization efficiency between the TX and RX antenna. The simulation results show that the impedance bandwidth of the $\mathrm{TX} / \mathrm{RX}$ antennas span from 5.65 to 5.924 GHz, with isolation within the operating band exceeding 24.9 dB. The axial ratio of RX antenna ranges from 5.752 to 5.859 GHz, exhibiting right-hand circular polarization, whereas the axial ratio of TX antenna spans from 5.75 to 5.855 GHz, demonstrating left-hand circular polarization. The overall size of radar module is $0.677 \lambda_{0} * 0.677 \lambda_{0} * 0.046 \lambda_{0}$.