Research On Passive Bearing Method Based On Three-Element Array

Submarine is one of the main underwater weapons,whose frank array passive sonar has drawn much attention as the main battlefield sonar.With the worldwide armament competition and the rapid upgrading of naval equipment,it has put forward higher requirements for the modern sonar system.The detection,identification,location and tracking of weak targets have become even more important.The conventional frank array direction finding system mainly uses the preformed multi-beam algorithm to obtain the space gain,and the inter-subarray cross-correlation(GCC)obtains the time gain to achieve the target direction finding.In this paper,the algorithm has been improved which bases on the existed direction finding system for the broadband noise.Following issues are mainly discussed in this paper:1.Describing the realization of the split sonar's direction in detail,which includes the physical basis,geometry,beamforming principle and the delay estimation theory.2.In the process of direction finding,the self-noise of the ship and the noise of main power unit will form the strong interference at a fixed angle,which is rather harmful to the detection and finding of the weak target.In order to address this problem,a Bartlett-based beam nulling algorithm is implemented to design the time-domain beam nulling,which makes the beamforming a directional zero point at a fixed angle and restrain the strong interference with its side-lobe.Based on the realization of this algorithm,the detection performance of weak targets of the passive directional system is improved.3.When the target of broadband noise is in the conventional beam of the pre-formed multi-beam with the signal from the non-main beam direction,the energy of the high-frequency part will leak.The time-domain constant beamwidth beamforming based on second-order cone programming is adopted to design the constant beamwidth in the frequency domain and the FIR filter coefficient in the time domain to ensure that the energy of the wideband signal after the array processing is not lost and the waveform is not distorted.Through the constant beamwidth preformed multi-beam overlap and cross-correlation process,it has achieved the function of the bearing system and improved the overall detection performance of the system.