Near-Field Effects on Micrometer Accurate Ranging With Ultra-Wideband mmWave Radar

We investigated near-field effects on free-space ranging with ultra-wideband millimeter-wave (mmWave) radar. In this application, one often assumes far-field conditions. However, with increasing requirements of accuracy, far-field assumptions are not satisfying. The radar measurements are affected by phase variations, leading to erroneous distance estimates. To simulate and approximate these effects, we propose computational methods by means of physical optics. They were validated using a state-of-the-art frequency-modulated continuous-wave radar sensor. Sophisticated experiments show good agreement; thus, in practice, the methods can be used to correct distance estimates to achieve micron accuracy without extensive calibration in advance.