Dual-Circularly Polarized STAR Antenna Array With High Realized Gain and Enhanced Isolation

A dual-circularly polarized antenna array with high gain and enhanced isolation for simultaneous transmit and receive (STAR) frequency modulated continuous wave (FMCW) radar application is proposed in this letter. The antenna element employs a combination of serial traveling-wave feeding, cross-aperture coupling and stacked parasitic patch to achieve wide impedance and circular polarization bandwidth. The utilization of the sequential rotation array technique not only enhances the axial ratio but also further improves the realized gain. Both decoupling feeding networks (inverse cancellation loop) and decoupling spatial structures (Jerusalem cross) are adopted to achieve high isolation in a wide frequency range by obtaining two decoupling nulls. Measurement results demonstrate that the −10 dB impedance bandwidth of the antenna array exceeds 42% [(2 to 3) GHz], while its 3 dB axial ratio bandwidth surpasses 33.3% [(2 to 2.8) GHz]. In the 2.3 GHz to 2.5 GHz FMCW radar band, mutual decoupling is greater than 30 dB with a realized gain exceeding 13.5 dBic and axial ratio less than 1 dB.