A Novel Data-Based DC Offset Calibration Technique for Millimeter-wave Interferometric Sensing of Weak Displacement Motions

The millimeter-wave radar benefits from the short wavelength exhibiting superior performance in sensing weak displacement motions. However, the phase demodulation accuracy can suffer from DC offset. The traditional calibration method struggles with weak displacement motions, which are significantly smaller than the wavelength, as inaccurate estimations result from fitting ultrashort I/Q signals onto the unit circle trajectory. Moreover, this method entails computational complexity. This paper proposes a data-based DC offset calibration technique. It directly utilizes pre-sampled DC values for signal calibration, which is suitable for subtle displacement sensing and simplifys computational demands. The impact of the static clutter reflections on target detection in the experimental environment is analyzed. Experimental results using a 24 GHz interferometric radar show that the proposed technique enables the precise deep sub-wavelength displacement motion detection of 1/104 wavelength with a relatively low root mean square error (RMSE) of 23.06 μm and a weak motion of 1/15.625 wavelength is reconstructed with the relative RMSE (RRMSE) < 4.1%.