Fast Frequency-Domain Generalized Radon–Fourier Transform for ISAR Imaging of Maneuvering Ships

Complex rotational motion of a ship induces severe range migration and time-varying Doppler modulation in radar echoes. The time-domain generalized Radon–Fourier transform (TGRFT) can jointly compensate for these effects, but its multidimensional search over the initial range and all motion coefficients leads to a high computational burden. This paper proposes a two-dimensional frequency-domain GRFT (2D-FGRFT) for fast motion-parameter estimation and inverse synthetic aperture radar (ISAR) imaging of ships. The two-dimensional frequency-domain expression of a radar echo with a polynomial slant-range history is first derived, based on which a corresponding frequency-domain matched filter is constructed. The matched filter is parameterized only by the second- and higher-order frequency-domain motion coefficients. By exploiting the structure of the derived expression, a two-dimensional inverse fast Fourier transform (2D-IFFT) is performed after matched filtering, replacing the explicit searches over the initial range and first-order motion coefficient while preserving coherent integration of echoes from multiple scatterers on the ship. Finally, the motion parameters are determined from the matched-filter parameters and the peak locations obtained through constant false alarm rate (CFAR) detection, enabling fast ISAR imaging of the ship. Computer simulations and experimental results validate the computational efficiency, noise robustness, and overall performance of the proposed algorithm.