Miniaturized Circularly Polarized Patch Antenna Based on a Non Uniform Metasurface for Ultra Wideband Radar Systems

High-gain circularly polarized antennas are crucial for biomedical systems, particularly for detecting vital signals such as heartbeat and respiration. Metasurfaces can significantly enhance the performance of antennas in highly space-constrained environments by providing benefits such as gain improvement and polarization conversion. In this work, a miniaturized circularly polarized patch antenna integrated with a metasurface was designed for a UWB radar operating in the 3.1 to 4.8 GHz frequency band. By leveraging the polarization conversion effect of the metasurface, a non-uniform structure was realized that introduces a phase difference between the metasurface elements, resulting in a more compact antenna design. Following the design stage, both the antenna and the integrated metasurface were fabricated. A low-cost FR-4 substrate was used for the patch antenna, while Rogers RO3003 was used the metasurface substrate. Measurement results demonstrate that the metasurface-integrated patch antenna achieves a 3 dBi gain enhancement and maintains circular polarization within the 4 to 4.8 GHz frequency range, with an axial ratio below 3 dB.