High-Precision ISAR Imaging for Microwave Photonic Radar: Compensating Spatial-Variant RCM and Component Phase Errors

Microwave photonic technology has revolutionized conventional radar systems, enabling the imaging of critical components on non-cooperative airborne targets, such as engines and wings. However, the wide bandwidth and extensive rotation angle of Microwave Photonic Inverse Synthetic Aperture Radar (MWP-ISAR) pose significant challenges for achieving precise imaging. Specifically, correcting the spatially variant characteristics of the high-order components of range cell migration (RCM) in MWP-ISAR proves challenging. Additionally, variations in the scattering characteristics of different structural components introduce unknown component phase errors, further complicating existing imaging algorithms. To address these challenges in MWP-ISAR imaging, an innovative approach is introduced. The core of this algorithm lies in utilizing the energy trajectory of the echo to accurately estimate the motion parameters of non-cooperative target. The proposed method ensures high-precision correction of multi-order RCM through the reconstructed motion trajectory, concurrently extracting and compensating for unknown structural phase errors. The paper initially establishes the MWP-ISAR echo model, providing detailed insights into the trajectory reconstruction and multi-order RCM simultaneous correction algorithm. Despite the correction of RCM, residual unknown component phase errors in the echo continue to impact imaging quality significantly. To mitigate this, a phase compensation algorithm is introduced. Building on preliminary imaging results, a separation processing algorithm is devised to isolate echoes from each structural component. Subsequently, an autofocus algorithm is employed to precisely estimate phase errors for each structural component. Ultimately, the proposed method combines high-precision imaging results for all components, yielding a well-focused target image. The efficacy of the approach is substantiated through rigorous numerical simulations and real measurement data.