Abstract: It is one of the main trends in mordern sonar development to use a low frequency line array of large aperture,e.g.a towed line array and a flank array,etc.These arrays generally operate in a background noise where the turbulent flow fluctuations and the directional noise from self——ship are the dominant noise components.In order to eliminate the influence of the noise disturbances on their performance,the segmentation broken line model of a densely spaced large array and the fractional beamforming technique are presented in this paper,which are based on the physical properties of the background noise and have been a break through on the treditional concept of an array with half——wavelength spacing between elements.
The influence of array shape distortion and the reduction method of its distortion lOsses for the array model have also been analysed and simulated by a computer.The result shows that not only the SNR gain of the array is raised by about0 dB,but also the self——noise level is considerably decreased.It also shows that the complexity of signal precessors is obviously simplified and the sensitivity of element location uncertainty to the array performance is reduced.As a result,the Performance Figure of the passive detection system is greatly increased.