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

Microwave photonic technology has transformed conventional radar systems, enabling the imaging of critical components on non-cooperative airborne targets like engines and wings. However, the wide bandwidth and extensive rotation angle of Microwave Photonic Inverse Synthetic Aperture Radar (MWP-ISAR) present significant challenges for precise imaging. Correcting the spatially variant characteristics of high-order range cell migration (RCM) in MWP-ISAR is particularly difficult. Additionally, variations in the scattering characteristics of different structural components introduce unknown phase errors, complicating existing imaging algorithms. To address these challenges, a novel approach is introduced. The core of this algorithm uses the energy trajectory of the echo to accurately estimate the motion parameters of non-cooperative targets. This method ensures high-precision correction of multi-order RCM through the reconstructed motion trajectory and simultaneously extracts and compensates for unknown structural phase errors. The approach begins by establishing the MWP-ISAR echo model, detailing the trajectory reconstruction and multi-order RCM correction algorithm. Despite correcting RCM, residual unknown phase errors in the echo continue to impact imaging quality. To mitigate this, a phase compensation algorithm is introduced. Based on preliminary imaging results, a separation processing algorithm isolates echoes from each structural component. Subsequently, an autofocus algorithm is employed to precisely estimate phase errors for each component. Ultimately, the method combines high-precision imaging results for all components, yielding a well-focused target image.