Analysis of multipath effects in automotive MIMO-SAR

This paper analyzes the concept of multipath in automotive radar imaging, particularly in MIMO-SAR imaging. In a typical automotive environment, the radar signal may experience multiple reflections, which leads to the presence of ghost targets in the focused image. These targets may trigger undesired maneuvers from an advanced driving assistance system (ADAS), resulting in possible accidents. In this paper, we show how the position and brightness of the ghost targets are inherently related to the radar's physical layout, including the number of transmitting and receiving elements and their positions. Accordingly, we strongly recommend avoiding the usage of any monostatic or bistatic equivalence in simulation software since they will result in entirely erroneous results. We also show how MIMO-SAR, if implemented with the MIMO aperture orthogonal to the SAR aperture, is intrinsically robust to double bounces resulting in the suppression of ghost targets due to this effect. A set of simulations representing typical automotive scenarios support the theoretical analysis.