A Correction Method for the Nonlinearity of FMCW Radar Sensors Based on Multisynchrosqueezing Transform

The frequency-modulated continuous wave (FMCW) radar sensors have attracted much attention in short-range applications. However, when detecting a stationary target, an FMCW radar sensor obtains the time-varying beat signals due to its nonlinearity, which degrades the imaging quality. For this reason, a correction method for the nonlinearity of FMCW radar sensors is proposed based on the multisynchrosqueezing transform (MSST) in this article. First, a reference beat signal is processed by the short-time Fourier transform (STFT) to generate the blurry time–frequency (TF) representation. Second, an iterative reassignment procedure is employed to concentrate the blurry TF representation by the MSST method. Then, the concentrated TF representation is used to estimate the nonlinear coefficients by ridge detection and polynomial fitting. Finally, the nonlinear beat signals are compensated using the nonlinear coefficients after time resampling. The effectiveness of the proposed method is validated by simulations and experiments. The results show that the proposed method can obtain more concentrated TF representation and more accurate estimation of nonlinear coefficients, resulting in a higher quality of range profiles and synthetic aperture radar (SAR) images. In addition, the proposed method has better noise robustness for the strongly time-varying and multicomponent beat signals.