On Low-Oversampled ST-Staggered SAR Signal Reconstruction Scheme

Staggered synthetic aperture radar (SAR) innovatively proposes to achieve ultra-wide-swath continuous imaging without azimuth resolution degraded by changing the pulse repetition interval (PRI). Existing research mainly focuses on azimuth signal reconstruction under low oversampling ratios. However, staggered SAR still faces significant challenges of echo overlap, and the system performance is degraded further by ultra-broad-beam illumination. This study introduces a concept combining space-time waveform-encoding (STWE) with staggered SAR, namely ST-Staggered SAR. The core idea involves the introduction of null constraints and time-division transmission of sub-pulses to enhance the system's range ambiguity-to-signal ratio (RASR) and noise equivalent sigma zero (NESZ) performance. In addition, the study provides a comprehensive two-dimensional signal processing flow for ST-Staggered SAR. Considering the transmission characteristic, a linearly varying PRI sequence design criterion is analyzed, in which the proposed adaptive elaborated PRI variation sequence reduces the extended blind range overlap largely. For range signal reconstruction, the study deduces the overlap echo model and clarifies the digital beamforming (DBF) with null constraints processing flow of the system. Regarding azimuth signal reconstruction, a two-step reconstruction scheme is established, using truncated nuclear norm regularization (TNNR)-based low-rank matrix completion (LRMC) for blockage recovery and best linear unbiased (BLU) estimation for uniform resampling. Simulation experiments demonstrate the feasibility of the proposed concept and the effectiveness of the signal reconstruction scheme.