Inverse synthetic aperture radar imaging of nonuniformly rotating target via time-weighting azimuth focusing method

Inverse Synthetic Aperture Radar (ISAR) imaging of the nonuniformly rotating target (NURT) is a very common case in practical applications. In this case, the Doppler frequency in cross-range domain of the received signal is time-varying because of the complex rotational movement, thus the frequency spectrum obtained by Fourier transform is broadened. Therefore, the traditional Range-Doppler (RD) processing is no longer appropriate for the azimuth focusing. The Fractional Fourier transform (FrFT) is also invalid because of the different fractional order of the signal components. Approaches based on time-frequency analysis can effectively solve the imaging blurring problem, however, the computational complexity increases significantly. In this paper, a novel approach for ISAR imaging of the NURT via Time-Weighting Azimuth Focusing (TWAF) method is proposed. It employs the differential property of the Fourier transform, which makes the cross-range profiles of the echo signal to be better focused. Furthermore, it yields extremely low computational complexity, and no rotational motion compensation (MOCOMP) is required. Simulation results validate the effectiveness of the proposed method on ISAR image deblurring.