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Dynamic ISAR imaging of the maneuvering target based on the instantaneous amplitude and chirp rate estimation

XING Meng dao,BAO Zheng,FENG Da zheng (National Key Lab. of Radar Signal Processing, Xidian Univ., Xi′an 710071, China)[  
Most of dynamic Inverse Synthetic Aperture Radar (ISAR) imaging methods for maneuvering target are based on time frequency distribution, and the assumption that the scatterers echo has a constant amplitude and linear frequency modulation. In fact, when the target has dihedrals and trihedrals components, or scatterers exist in Migration Through Resolution Cells (MTRC), or the scatterer moves in or out of the analyzing range cell, all this results in the fact that the amplitude is not constant, and for a maneuvering target, the Doppler of the scatterers echo after translational motion compensation is time varying. In order to solve this problem, we use multicomponent amplitude modulation and linear frequency modulation (AM LFM) signals to approximate the scatterers echoes, and we propose a fast algorithm for estimating the amplitude and chirp rate, with the algorithm first to find the frequency modulation rate of one component by dechirping searching, second to demodulate this component to an amplitude modulation sinusoidal signal, third, to spearate and clean this component in Fourier domain, and estimate the instantaneous amplitude, then to estimate for the next component, and finally to obtain all scatterers instantaneous amplitudes and frequencies, so that dynamic ISAR images are obtained. Images obtained by this method from the real date are better than those obtained by other methods, which helps automatic target recognition (ATR) and lead to the small computation load.
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