Retrodirective Electromagnetic Pavement Markers for Enhanced Automotive Radar Vision

Pavement markers play a critical role in ensuring the road safety and the guiding of drivers, particularly in adverse weather conditions where visibility is compromised. However, traditional detection methods using cameras and LiDARs often struggle to accurately detect road markings in such conditions, especially when factors like rain, fog, dust, and snow are considered. By contrast, radar technology offers a promising potential in recognizing these markers even in severe weather conditions and at long ranges, provided they are engineered to reflect the radar signals effectively. In this work, a low-cost, low-profile mmWave retrodirective surface capable of retrodirecting the signals emanating from an automotive radar was designed and tested. First, the design and test of a planar Substrate-Integrated-Waveguide (SIW) vertically-polarized horn antenna forming the basis of the electromagnetic marker is described, demonstrating a gain of 13 dBi and an 3-dB azimuth beamwidth of 21. Then, the arraying of this horn antenna using a Van Atta scheme for 1 to 3 pairs and the stacking of these arrays up to 5 layers is shown and the performance of these assemblies is characterized, displaying a maximum Radar-Cross-Section (RCS) of -16 dBsm and an azimuth coverage of 30. Finally, the pavement markers are tested in road-like conditions, displaying the ability to be detected and imaged at distances up to 25 m on different pavement surfaces and with the interference of snow, mud, ice, and rain. This low-cost electromagnetic pavement marker design—similar in dimensions and cost to conventional raised reflective optical markers—could set the foundation for the widespread deployment of safety and autonomy-enhancing electromagnetic road infrastructure for use by the now ubiquitous automotive radars that equip modern vehicles.