Instantaneous Frequency Estimation for Radar Signals Based on Improved Time-Frequency Distribution

Abstract：Instantaneous frequency (IF) estimation has great signality in radar signal processing. Detecting the peak of time-frequency distribution is an effective approach for IF estimation, but error usually occurs when some points outside the signals’ auto-term surpass values of the peak of time-frequency due to false maxima detection in noise environment. To estimate the IF accurately in the condition of low SNR, a hybrid time-frequency distribution method is proposed, which combines the Wigner-Ville Distribution(WVD) and Choi-Williams Distribution(CWD) based on the Hadamard product of time frequency matrices. Simultaneously, the time-frequency distribution of the noise is suppressed by adopting time-frequency energy integration. The probability that the time-frequency distribution takes a maximal value outside the auto-term position is considered as the guide line for selecting the window length of time-frequency analysis, and then the initial IF is estimated. The intersection of the confidence intervals algorithm is applied to detect the IF along with initial IF finally. The proposed approach is employed to estimate the IF of NLFM, LFM and FSK signals, and compared with the method of the first moment of the time-frequency distribution and the peak of the WVD. The validity of the proposed method is demonstrated by experiments.