High-Resolution Imaging of Maneuvering Targets in Microwave Photonic ISAR with Improved Variable Mode Decomposition Techniques

Microwave Photonics Inverse Synthetic Aperture Radar (MWP-ISAR) is an emerging imaging radar system that integrates photonics technology. By utilizing low-frequency ultra-wideband signals, MWP-ISAR achieves centimeter-level imaging precision for high-value targets. However, challenges persist when attempting to achieve high-precision imaging of maneuvering targets in airborne and maritime scenarios. Two main issues arise: (1) Non-cooperative target motion introduces 2-D spatial-variant phase errors in the echoes due to the high resolution. (2) Target maneuvering induces time-varying phase characteristics in the echoes. Existing autofocus and motion compensation algorithms struggle to address both spatial-variant and time-varying phase errors effectively. In this paper, a high-precision imaging algorithm for maneuvering targets is proposed, based on an improved Complex Variable Mode Decomposition (CVMD) approach. Firstly, the MWP-ISAR echo model for maneuvering targets is established, and the rationality and advantages of applying mode decomposition algorithms to ISAR imaging of maneuvering targets are investigated. In particular, the advantages of the CVMD method for resolution enhancement in small angle imaging. Subsequently, an ISAR imaging process is devised based on the CVMD algorithm. To enhance the performance of the CVMD algorithm and tackle the challenge of solving its parameters, a brute-force optimization algorithm is introduced. This strategy can effectively overcome the problem of difficulty in determining the decomposition mode number of the CVMD algorithm. Finally, high-resolution imaging of maneuvering targets at small turning angles was achieved. The effectiveness of the proposed algorithm is validated through multiple sets of simulation data and real MWP-ISAR data.