RPIT: Multiscatterer Coherent Integration for Range-Spread High-Speed Maneuvering Targets via Range-Phase-Invariant Transform

High-speedmaneuvering targets in radar systems induce range migration and Doppler frequency migration. These effects make coherent integration difficult. Existing methods can handle these issues for point targets in narrowband radars. However, because they cannot achieve coherent accumulation across outputs from different scatterers for range-spread targets (RSTs), their performance drops in wideband systems, where the target energy spreads over multiple range cells due to multiple scatterers at different radial positions. This article first shows that the unknown initial phase and range of scatterers limit coherent accumulation. To address this problem, we propose a coherent integration algorithm for RSTs based on the Range-Phase-Invariant Transform (RPIT). Unlike conventional methods, the proposed algorithm is invariant to both the initial phase and the range of scatterers. It has two key properties: First, the output depends only on the scatterer velocity, which enables position alignment across scatterers; and second, the output is real-valued, which enables phase alignment across scatterers. These two properties ensure coherent accumulation among multiple scatterers. This is the most important difference between the proposed method and existing approaches. Theoretical analysis and simulation results show that the output signal-to-noise ratio gain of RPIT lies between 10 log₁₀ (K) dB and 10 log₁₀ (K²)dB, where K is the number of scatterers, and exceeds that of existing methods. Moreover, the proposed method avoids joint searches in multidimensional parameter spaces and thus reduces computational complexity. Finally, simulation results show that when K is large, the proposed RPIT achieves the best detection performance, and real data results further verify its effectiveness.