Phase Difference Compensation Method for Range Estimation in an MFCW–CW Radar

Multifrequency continuous-wave-continuous-wave (MFCW-CW) radars simultaneously transmit multifrequency continuous-wave (MFCW) signals sequentially at a constant time step and a continuous-wave (CW) signal constantly. As MFCW signals are transmitted sequentially, only one phase difference exists at each time. All phase differences between the MFCW and CW signals should be exploited to resolve ambiguous ranges. In this article, we propose a method to compensate the phase difference between the sequential MFCW signals and CW signal using the Doppler frequency of the CW signal. To verify the phase difference compensation result, we estimated the range of multiple targets. The simulation results showed that the proposed phase difference compensation method performed well regardless of compensation direction and target motion. Moreover, we proposed applying the maximum likelihood estimation (MLE) and reduced-complexity off-grid sparse Bayesian learning (RC-OGSBL) to estimate ranges and analyzed their performance. The range accuracy of the MLE using a 0.1- m grid search showed superior performance and the running time of the MLE using the simple method is the fastest among the simulated methods. The RC-OGSBL using a 5- m grid showed good results in terms of range accuracy and running time.