Research On Virtual Array Method Of Broadband Beamforming

Beamforming is an important technology in sonar signal processing. For the simplicity, easy to implement and robustness under low signal to noise ratio and less samples, conventional beamforming is still being widely used in practice. But the inverse proportion of beamwidth to the aperture makes it lack of space resolution. In order to improve the performance of the array, new beamforming method is necessary to be adopted. It has been verified that virtual array method is a feasible one. It can increase the resolution without changing the array length.As for the uniform linear array, the beamforming principle and beam optimization design is firstly illustrated in the thesis. With the above analysis, two virtual array algorithms for narrowband signal are studied: one is based on the phase information of the received signal; the other includes the characteristics of the array expansion based on fourth-order cumulant. Computer simulations of them show that each one can improve the resolution obviously compared to the conventional method. To the broadband signal beamforming, a new method of virtual array is proposed in the thesis. Based on time delay and preformed multi-beam, this method enhances the resolution under some condition. After this, constant beamwidth beamforming by chebyshev-weighted method is also simulated.Except for the simulation analysis, all the methods presented in the thesis are verified by the experimental data obtained from SONG HUA Lake. Comparison between the results show that the virtual array method is right and has good meet with the conventional.