Broadband matching of high-permittivity coatings with frequency selective surfaces

Due to design restrictions, future automotive radar sensors within the 79GHz band need to be integrated behind painted, plastic fascia (e.g. a painted bumper) for advanced driver assistance systems. Reflections from the bumper, which is in the line-of-sight of the sensor, might lead to undesirable performance degradation. To reduce these reflections, impedance matching of multilayer structures with high permittivities (e.g. metallic paints) is necessary. Next to conventional matching techniques, frequency selective surfaces (FSS) can be freely designed to realize a matching layer. For four possible structures a bandwidth evaluation is shown. The measurement and simulation results revealed that for a bandwidth of 4 GHz, the proposed solution (single cross structure) outperforms state of the art matching techniques.