A Passive Circularly Polarized Van Atta Reflector For Vehicle Radar Applications

This letter proposes a planar passive circularly polarized (CP) retrodirective antenna (RDA) array for vehicle radar applications. Different than the linearly polarized RDA arrays, the retrodirective signal generated by the CP RDA arrays can easily be extracted due to the orthogonal polarized character of the scattering and retrodirective signals. Circular polarization is achieved by a substrate integrated waveguide cavity-backed antenna. Moreover, the low-loss and nondispersive substrate integrated coaxial lines are employed as the feeding networks to expand the operating bandwidth for the large array. Measured results of bistatic and monostatic radar cross section verify the designed prototype, showing that the CP RDA array covers a scan angle of at least ±30° from boresight without interference by sidelobes. The measured bandwidth of the retrodirective property is 24.85-25.45 GHz. The capability of CP retrodirectivity ensures that the proposed RDA array is a good candidate for short-range vehicle radio equipment.