Frequency-Domain Decoupling and Subband Synthesis-Based Adaptive Monopulse for Distributed Coherent Aperture Radar in Multidirectional Jamming

Abstract

Due to the long baselines and sparse aperture structures of distributed coherent aperture radars, jamming signals from multiple directions exhibit a dispersion phenomenon, where the steering vectors depend on both angle and frequency. This significantly complicates interference suppression and impairs the accuracy of subsequent target angle estimation. To address these challenges, this article proposes an adaptive monopulse angle measurement method based on frequency-domain decoupling and subband synthesis. First, the range cell migration effect of the target signal is eliminated through frequency-domain beam steering, thereby decoupling the target steering vector from frequency. Second, a subband adaptive processing strategy is adopted to suppress frequency-dispersive multidirectional jamming within each subband. Finally, the full-band signal is coherently synthesized in the frequency domain to improve the detection gain, and an iterative formula for adaptive monopulse under full-band synthesis is derived to achieve high-precision angle estimation. Theoretical analysis and simulation results show that the proposed method can effectively suppress multiple dispersive jamming signals in sparse nonuniform array structures. The output signal-to-interference-plus-noise ratio approaches the optimal value, while the root mean square error of angle estimation closely matches the Cramér–Rao lower bound.