Passive Synthetic Aperture Equivalent Model and Localization for Spaceborne Squint Scenario

In wireless emitter monitoring scenarios, space-borne passive localization technology has garnered significant attention due to its advantages such as wide-area coverage and all-weather operation. Conventional localization methods, such as Direction of Arrival (DOA) and Frequency Difference of Arrival (FDOA), rely on instantaneous measurements and process signals non-coherently over time. Consequently, their accuracy degrades significantly under low signal-to-noise ratio (SNR) conditions. In recent years, passive synthetic aperture (PSA) techniques have been applied to emitter localization, enhancing localization precision through coherent integration of the Doppler phase to achieve high processing gain. An accurate PSA method requires precise modeling of the Doppler history. However, existing models predominantly assume linear platform motion, which introduces a fundamental model mismatch by neglecting orbital and Earth curvature effects. This omission leads to inaccuracies in Doppler history reconstruction and ultimately limits their applicability in practical spaceborne missions. To address these limitations, this study first establishes an equivalent squint model for spaceborne passive localization scenarios, then provides rigorous definitions of the equivalent parameters, and finally proposes a PSA localization method tailored for spaceborne squint conditions, thus extending the applicability of the spaceborne PSA method to squint scenarios. Experimental results show that the proposed method achieves an order-of-magnitude improvement in localization accuracy over conventional FDOA and DOA methods under low-SNR conditions, while maintaining high-precision localization capability despite large squint angles. The practical efficacy of the approach is further confirmed via a satellite experiment.