Research On Target Micro-Doppler Feature Extraction Technology Based On S Transform

The micro-Doppler effect refers to the phenomenon that the micro-motion of the target produces frequency modulation on the radar echo signal.The micro-Doppler information can accurately describe the motion characteristics and physical structure of the target,which provides a new direction for the RATR technology.In recent years,the research of micro-Doppler effect has received widespread attention,but its technology is still not mature.In this paper,extraction methods of micro-Doppler feature based on S Transform are mainly studied.The main work of this paper is as follows:(1)Based on the theory of micro-Doppler effect and the mathematical model of vibration,rotation and cone motion,the micro-Doppler echo signal model of rotor blade and the micro-motion model of aircraft rotor are established.In addition,the influence of the aircraft rotor's physical and motion parameters on the micro-Doppler echo signal is analyzed.(2)Based on the theory of time-frequency analysis,the principles and implementations of STFT,WT and WVD are studied.The performance characteristics and the effect on extracting micro-Doppler features of the three methods are analyzed through simulation.(3)Modified S Transform is proposed to solve the problem that S transform can not adapt to the large frequency variation of signal.Frequency companding is realized by constructing a window function,which effectively reduces the dynamic range of the frequency,so that the time window can be adapted to the frequency better.Besides,adjustment parameters are introduced to control the change trend of window,which can increase the flexibility of time-frequency analysis.The simulation results show that the Modified S Transform can effectively improve the frequency resolution and extract the micro-Doppler features better.(4)To solve the problem that the time-frequency resolution is constrained by the Uncertainty Principle in the traditional time-frequency domain,the modified S-transform is extended to the fractional domain,and the Fractional Modified S-transform(FRMST)is proposed and the specific implementation steps of FRMST are studied.This method obtains a fractional domain with the minimum TBP by rotating to an optimal order to realize high resolution of the frequency.The simulation results show that FRMST can break the constraints of time-frequency resolution,and effectively improve the time-frequency resolution.