Focused passive synthetic aperture

High accurate ranging for near-field sources requires that the array aperture should be long enough, especially for the weak underwater acoustic signal with very low frequency. The passive synthetic aperture technique can increase the array aperture artificially by the motion of physical array and signal processing. This paper applies it to the near-field ranging with focused beamforming, which provides a feasible ranging method for near-field weak signal. Theoretical analysis and simulation results both indicate: 1) the proposed method can achieve high ranging precision for near-field sources; 2) because of the error accumulation, the times of extending array would affect the ranging precision directly, and if the sizes of synthetic apertures are same, the fewer times array is extended, the better performance it owns, on the contrary, the ranging precision is independent on the speed of the towed array.