Impact of road surfaces on millimeter-wave propagation

Future intelligent transportation systems (ITSs) will deeply rely on millimeter waves for communication and sensing purposes. This results in the need of a precise description of the propagation properties at these frequencies. In this paper, the propagation mechanisms reflection and diffraction of millimeter waves at realistic road surfaces and geometries are investigated theoretically and validated by measurements at 77 GHz. The effect of guided waves underneath a vehicle's underbody is observed, which can be exploited in a favorable way for range extension in obstructed sight situations. It is also shown that the local curvature of common road surfaces leads to focusing and defocusing effects of the transmitted energy, resulting in an increased signal fluctuation. Furthermore, the importance of diffraction phenomena at road crests is stressed, which were formerly neglected but may play an important role in security sensitive applications like collision avoidance systems etc.