77 GHz Fully Polarimetric Antenna System With Compact Circularly Polarized Slots in Gap Waveguide for Automotive Radar

A fully polarimetric antenna system, designed using ridge gap waveguide (RGW) technology, is proposed, fabricated, and experimentally validated based on circularly polarized slots. The proposed slot element not only plays a role as a radiator but also works as a polarizer. Its geometry is very compact with aperture dimensions of
$0.44 \,\lambda _{0} \times 0.44\, \lambda _{0}$
and a profile depth of
$0.64 \,\lambda _{0}$
. The proposed antenna system has full circular polarizations (CPs) at both the transmitter (Tx) and receiver (Rx) and comprises four layers with the ability to directly integrate into a radar front-end. High port isolation (≥35 dB) between adjacent Rx channels is achieved by using thin decoupling walls and dummy elements to suppress mutual couplings (MCs). The measured results show an excellent field of view (FoV) (embedded axial ratio ≤3 dB) in the azimuth plane, with about ±60° at Rx and ±50° at Tx. The antenna system is engineered for low radar cross section (RCS) target detection and offers suppression of environmental noise. Experimental evaluation of the integrated radar module shows good agreement between simulation and measurement results. The work offers potential applications of such antenna systems in automotive radar systems, especially where polarization diversity and environmental robustness are required.