A Motion Target Refocusing Method Based on Range Frequency Difference Processing Without Parameter Search

Correcting the range migration of moving targets and compensating for the coupled phase errors are crucial for ground moving target imaging (GMTIm). Most methods achieve target focusing through parameter search operations with substantial computational complexity. In addition, the inability to address energy spreading caused by the higher order motion further limits the applicability of these methods. To overcome these issues, this article proposes a novel refocusing method without motion parameter estimation for arbitrarily moving ground targets. First, a range frequency difference (RFD) function without parameter estimation is constructed in the range frequency domain. Then, by conjugate multiplication with the RFD function, the coupling between range frequency and slow time of target can been removed. With an appropriate frequency interval selected, the target can also be azimuthally focused. In addition, some practical factors in applications are analyzed in detail. Compared with the traditional methods, the proposed method effectively addresses range migration and azimuth defocusing caused by higher order phase errors. Also, it achieves target focusing without search operations, despite the existence of Doppler center ambiguity and Doppler spectrum splitting. In addition, since it only requires fast Fourier transform (FFT), inverse FFT (IFFT), and matrix multiplication operations, this method achieves high computational efficiency. The efficacy of the proposed method is confirmed through the examination of both simulated and real data.