Design of a Polarization Rotating FSS for Polarimetric Automotive Radar Measurements

Polarimetric radars require multiple channels to transmit and receive orthogonal polarized electromagnetic waves for further characterization of targets compared to single polarized radars. A reliable characterization of targets is important for modern advanced driving assistant systems to analyze complex scenarios for highly automated vehicles. However, radar systems for automotive applications require to be robust, cost-effective and easy to integrate while polarimetric radars have increased hardware need with higher costs and failure rates. To overcome this, a single polarized radar sensor can be placed in front of a frequency selective surface, which allows a frequency-dependent polarization rotation. Thus, different polarized electromagnetic waves containing characteristic changes by the target can be converted to a single polarized electromagnetic wave. The designed surface reflects linear polarized electromagnetic waves and rotates their polarization by 0° or 90° in dependency of frequency. In this paper a frequency selective surface for frequencies between 77 and 81 GHz is presented. These frequencies support automotive short range radar applications making the reflector attractive for evaluation of target characterization in vehicles. The structure is designed for a 45° oblique incidence and is the result of scaling a reflector concept designed in previous research projects for lower frequencies. Its theory is applied to the design, a simulation model is constructed and manufacturing tolerances are analyzed. A measurement setup is established for evaluation of a prototype. The measurement results verify the concept and further improvements of the reflector for automotive applications are discussed.