Enhancing Transparent Circularly Polarized Antenna Performance for Automotive Applications

In this paper, the impact of the vehicle body on the transparent circularly polarized (CP) antenna’s performance when installed on the vehicle windshield has been investigated. The incorporation of an absorber layer on the vehicle floor to improve the antenna’s performance has been proposed. The study also evaluates how the placement of the antenna on the windshield affects its performance. Utilizing a transparent CP spiral slot antenna operating at 1.227 GHz and 1.575 GHz, the results reveal that the radiation performance of CP antennas on windshields significantly depends on their positioning. Additionally, the vehicle body affects the CP antenna’s radiation pattern and axial ratio (AR). We propose adjusting the antenna’s position and incorporating an absorber layer on the vehicle floor to address these effects. Notably, this absorber layer has the potential to simultaneously improve the performance of multiple antennas mounted on the windshield. The enhancement caused by this layer is verified through full-wave simulations and measurements. The impact of seats and four occupants inside the vehicle on the antenna’s performance in the presence of the absorber layer is also investigated. With the absorber layer and occupants present, the antenna achieves an AR beamwidth of 36° and 31° at 1.227 GHz and 1.575 GHz, respectively, in the $y^{\prime}z^{\prime}$ -plane.