Circularly Polarized Phased Array Antenna with a Linear-to-Circular Polarization Conformal Metasurface Superstrate for EnhancedScan Range

In this study, we propose a circularly polarized (CP) beam scanning antenna system that integrates a linearly polarized phased array antenna (PAA) with a linear-to-circular polarization conformal metasurface superstrate (CMS). The metasurface is composed of uniform unit cells, the geometry of which is optimized for electromagnetic response under normal incidence. However, when such a uniform cell metasurface is implemented with a planar profile, the wave radiated from the array becomes increasingly obliquely incident on the metasurface as the steering angle increases, inevitably degrading the polarization conversion performance and thereby limiting the achievable beam coverage. To address this issue, conformal curvature profiles are employed to mitigate oblique incidence across different scan angle regions. The transverse aperture dimension of the CMS is optimized, and three curvature profiles are optimized for different steering regions. Next, the antenna system was fabricated and assembled using separate 3D-printed jigs to maintain the respective CMS curvature profiles, and the corresponding jig was manually replaced during measurement. Using the corresponding CMS curvature profiles for different steering regions, the proposed CP PAA experimentally demonstrates CP beam steering to a maximum measured angle of approximately 45°. The measured AR remains below 3 dB at the investigated steering states, and the broadside-referenced scan loss at the maximum measured steering angle is approximately 1.8 dB.