Efficient Autofocus Chain for ISAR Imaging of Non-Uniformly Rotating Target

Conventional approaches to inverse synthetic aperture radar (ISAR) imaging of a non-uniformly rotating target are not optimal in terms of reconstructed image quality and/or computation time. Motivated by the problems of conventional approaches, we introduce an efficient autofocus chain for ISAR imaging of a non-uniformly rotating target. The most distinct feature of the proposed autofocus chain is found in the processing sequence to compensate for the phase error induced by the translational and rotational motion (RM) of the target. In contrast to conventional approaches, RM compensation is first implemented in the proposed autofocus chain immediately after range-alignment. Next, further focusing of the ISAR image is performed by estimating the residual phase errors, providing globally well-focused ISAR images. From the experimental results using real data sets, we can conclude that the proposed autofocus chain is highly efficient in forming ISAR images of a non-uniformly rotating target in terms of both image quality and computational efficiency.