For Continuous Wave (CW) Doppler radar sensors, the presence of hardware imperfections can result in a significant deterioration of the I/Q signal quality. Therefore, correcting the amplitude-phase imbalance of the I/Q signals and removing the DC offset is the basis of the Doppler radar measurement system. However, in close-range scenarios, the I/Q signals exhibit significant amplitude modulation, which degrades conventional parameter estimation techniques. To address these challenges, we propose an elliptic optimization correction (EOC) method. The method firstly obtains the initial calibration parameters through segmented Elliptic Correction (EC). Subsequently, an amplitude recovery term is incorporated into the parameter optimization process, thereby nearly completely eliminating the impact of unknown amplitude attenuation on parameter estimation. Simulation and experimental results demonstrate that the EOC method effectively overcomes the limitations of existing orthogonal imbalance correction techniques in the presence of unknown amplitude attenuation. In close-range measurement, two operational modes measurement with a mean absolute error of 3.5 μm.

I/Q imbalance, displacement measurement, Doppler radar, ellipse correction, amplitude modulation.