Passive Localization Method of Mixed Far-Field and Near-Field Sources Based on FrFT

Modern sonar systems are evolving towards large-scale and large-aperture arrays to achieve higher spatial processing performance. However, in applying large-aperture arrays, the traditional positioning models based on a single far-field or near-field assumption have significant limitations. To address this issue, this study proposes a joint positioning algorithm for mixed-field sources based on the Discrete Fractional Fourier Transform (FrFT). This algorithm innovatively models the mixed-field sources as the superposition of multi-component linear frequency modulation signals. By leveraging the characteristic that different field sources generate peaks at different orders in the FrFT domain, the positioning parameters of the mixed sources can be estimated through the peak positions and orders. Numerical results demonstrate the effectiveness of the proposed algorithm.