High-Fidelity Near-Field mmWave MIMO Radar Simulation via Polarized Path Tracing

Abstract

Accurate simulation of near-field millimeter-wave (mmWave) multiple-input multiple-output (MIMO) radars is essential for developing and validating high-resolution imaging systems, yet remains challenging due to large virtual apertures, multi-path propagation, and polarization effects that invalidate conventional far-field assumptions. We present a Shooting and Bouncing Rays (SBR) simulation framework that formulates radar signal transport analogously to physically based rendering, replacing far-field radar cross section approximations with spatially varying bidirectional reflectance distribution functions (BRDFs) to accurately model near-field scattering. Path tracing enables tractable multi-bounce simulation, while importance sampling over antenna gain patterns and BRDFs, combined with next-event estimation for TX–RX connections, significantly improves convergence. Polarization is incorporated via a three-dimensional Jones vector formulation, enabling correct modeling of polarization-dependent scattering across multi-bounce ray paths. Quantitative and qualitative evaluation against real measurements from a 72–82 GHz high-resolution MIMO imaging radar demonstrates faithful reproduction of real radar returns, including challenging corner reflector scenes dominated by multi-bounce returns. Ablation studies confirm that multi-path modeling, polarization, and BRDF importance sampling are each essential for high-fidelity radar simulation.