A Novel Inverse Synthetic Aperture Radar Imaging Method for Maneuvering Targets Based on Modified Chirp Fourier Transform  
Yakun Lv  
1 Department of Electronic and Optical Engineering, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (Y.L. ); mail2 [EMAIL_ADDRESS] (Y.W. ); [EMAIL_ADDRESS] (H.Z.) [PERSON]  
2 Space Security Research Center, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (3) School of Space Information, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (Y.S.) [PERSON]  
1 Department of Electronic and Optical Engineering, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (Y.L. ); mail2 [EMAIL_ADDRESS] (Y.W. ); [EMAIL_ADDRESS] (H.Z.) [PERSON]  
3 Space Security Research Center, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (Y.S.) [PERSON]  
3 Space Security Research Center, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (Y.S.) [PERSON]  
3 Space Security Research Center, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (Y.S.) [PERSON]  
3 Space Security Research Center, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (Y.S.) [PERSON]  
3 Space Security Research Center, Space Engineering University, Beijing 101416, China; yhgnaw@163. (RWT) [9; 10], chirp Fourier transform (CFT) [11; 12], adaptive Chirplet decomposition [13], and sub-echo clean separation [14; 15; 16]. Among them, the JTFD method uses range-instantaneous Doppler (RID) to image, where the instantaneous Doppler is obtained by time-frequency analysis. However, the imaging quality of the JTFD method depends on the time-frequency method used, and the time-frequency resolution of different methods varies. At present, there is no method that combines both time domain and frequency domain resolution. The WVD method has a high time-frequency resolution, but there are cross terms, and the imaging quality is easily affected by the cross terms. The RWT, CFT, adaptive Chirplet decomposition, and sub-echo clean separation methods are essentially parameter estimation methods [17; 18]. These methods model the signal echo as a multi-component model, and then estimate or separate the sub-component parameters one-by-one to achieve high-resolution imaging. The computational demand of these methods is huge, and the algorithm efficiency is low, so they do not meet the requirements for ISAR real-time imaging. Research shows that target approximation satisfies the first-order linear motion with a short imaging time, so the target scattering point azimuth echo signal can be approximated as a multi-component chirp signal (LFM) [1]. The ratio of the quadratic phase term (chirp rate) to the first-order phase term (central frequency) of the scattering point echo signal is approximately a fixed value and equal to the ratio of the target rotational angular acceleration to the rotational angular velocity [19; 20]. Given this feature, an imaging algorithm based on matched Fourier transform (MFT) [21] is proposed in this study, but this algorithm only uses a single sub-echo signal for parameter estimation and the estimation error is large. A modified Fourier transform [22] is also proposed to modify the phase kernel function of Fourier to realize azimuth focusing. This method needs to reconstruct the phase function. The value of column vectors is strictly selected when reconstructing, and the reconstructed phase function is no longer the phase function of fast Fourier transform (FFT), which affects the speed of calculation. Based on the above analysis, this paper proposes a modified chirp Fourier transform (MCFT) maneuvering target imaging method.