Rapid Indoor Mapping and Non-Line-of-Sight Imaging Using a 228-GHz FMCW Polarimetric Radar System

In this article, a polarimetric millimeter-wave (MMW) frequency-modulated continuous-wave (FMCW) radar operating in the 222–228-GHz frequency range is proposed for mapping applications in indoor environments. Equipped with a mechanically scanning fan-beam reflector antenna with 360° field of view (FOV), the radar can generate 2-D images of its scene, offering LiDAR-like azimuthal resolution of 0.3°. The system’s performance for indoor mapping as well as line-of-sight (LOS) and non-LOS (NLOS) obstacle detection tasks is demonstrated in building corridors. The measurement scenarios include various wall types and wooden doors with metallic frames. The overall corridor map is created by taking multiple radar images and combining them through postprocessing. Given the strong presence of ghost targets in the radar images, an algorithm is developed for NLOS target detection and localization. As a foundation for this investigation, the wave reflection coefficients of painted drywall for both vertical and horizontal polarizations, $\Gamma _{VV}$ and $\Gamma _{\text {HH}}$ , are measured. Based on these results, a novel technique for NLOS target identification using polarization discrimination is proposed and experimentally verified. This technique is further tested in a realistic scene, where an L-shaped corridor is mapped using the polarimetric radar measurement, and NLOS targets are detected and localized using a mirroring transformation.