Transceiver Optimization With Transmit Element-Doppler Coding for Range Ambiguity Mitigation in SAR Imaging

A novel Transmit Element-Doppler Coding (TEDC) scheme is developed to mitigate range ambiguity in Synthetic Aperture Radar (SAR) imaging. The architecture integrates a spatial-temporal coding factor across transmit channels and slow-time pulses using linear frequency modulated waveform. To this end, a sub-aperture-based Doppler filtering approach is proposed to achieve additional Degrees-Of-Freedom (DOFs) exploiting the range ambiguity index in the azimuth frequency domain, thereby enabling the discrimination of echoes from various range ambiguity regions via transceive beamforming. To further enhance range ambiguity mitigation, a transceiver optimization problem is formulated with the objective of maximizing the Signal-to-Ambiguity-plus-Noise Ratio (SANR), subject to practical constraints on the transmit coding factor and transceive filter. To address this NP-hard non-convex optimization, a tailored Maximum Block Improvement (MBI) algorithm is devised. Specifically, in each iteration, variables are alternately examined by leveraging either closed-form expressions with hidden convexity properties or the minorization-maximization approach, and the variable yielding the greatest improvement in the objective function is updated. At the analysis stage, the convergence behavior of the devised optimization algorithm is examined under the Karush-Kuhn-Tucker framework. Simulation results validate the effectiveness of the TEDC-MBI approach in achieving range-unambiguous SAR imaging and demonstrate improved SANR performance compared to existing methodologies.