Bi-static Reflectivity Measurements of Vulnerable Road Users using Scaled Radar Objects

Current developments indicate enormous potential for improving environmental awareness through joint communication and radar sensing. In this respect, future wireless propagation channel models aim at including bi-static reflectivities of road users, depending on different illumination and observation angles, in the nearfield as well as in the far-field. The limitations of the measurement distances within anechoic chambers might generically suffer from nearfield effects, especially for electrically large radar objects like realistic road users, and conventional bistatic RCS calibration techniques would eventually fail. In order to model the transition from the nearfield to the far-field reflectivity of road users, this paper follows the object scaling approach. Bi-static reflectivity measurements of selected vulnerable road user models are described, from the chamber setup all the way up to data post-processing. The approach of electromagnetic object scaling is applied to such bi-static reflectivity measurements, and the results are evaluated and discussed. Initial proof-of-concept measurements of differently sized metal spheres verify the scaling approach under far-field conditions very convincingly. Based on this, scaled models of radar objects, namely a bicycle and a pedestrian, were 3D printed and then metallized with copper paint. Compared to corresponding electromagnetic simulations of the original bi-static reflectivity of the radar objects, the results measured for the scaled models show impressive agreement with the numerical expectation. This study contributes to the further development of future wireless channel models considering bistatic multipath components of different road users, being an indispensable prerequisite to enhance the safety in future road traffic.