Research On Virtual Array Extension

Angular resolution is limited by the aperture of array, which is called Rayleigh limit. The purpose of this thesis researched the algorithms which can extend array aperture, with which the received signal in the place out of the aperture can be deduced by the real received signals. In other words, it is equal to extend the array aperture, and enhance the angular resolution.The principles of beamforming and the foundation of vector array processing is introduced briefly, which is used as post processing when the virtual receive signal is constructed. Secondly, three methods to extending array aperture are researched, which are four-order cumulants, signal extrapolation and array interpolation. The use of cumulants in narrowband signal array processing is interpreted, which can eliminate Gauss noise, and extend aperture two times longer than that of original array. The application of cumulants to vector hydrophone array is proposed in this thesis. Signal extrapolation modified is used in underwater array processing in this thesis, which used Bartlett spatial spectrum as a priori knowledge. Normally, array interpolation is unfit for extending array aperture, and it is just used for virtual array transform. It is shown that a new array interpolation method whose combine with autoregressive models in this thesis can extend array aperture, which can extend array aperture. This thesis has made modeling theoretically, simulating experiment, and compared performance for each algorithm.Simulation results verify that effect based on four-order cumulants is best, whereas it need more computation than others. Signal extrapolation could not distinguish two targets when the targets are close to each other, and the precise of signal deduced depend on the number of targets. Array interpolation method also needs information of the number of targets. In the last,the experimental data obtained from lake experimentation was disposed. It is proved that the effect processed with each of three algorithms had much improvement than beamforming did.