Research On Nulling Widening Technique Based On Adaptive Beamforming

As an important research direction of array signal processing, beamforming technology has been widely applied in radar, communication, sonar, etc. Ideally, the adaptive beamforming algorithm will directs the null of beam pattern at the interference. But actually, the disturbances due to interference or vibration of the antenna platform remove out of null position which can not be effectively eliminate, and seriously affect the performance of the system. Therefore, the study of adaptive null control algorithm becomes very necessary. This paper studies the nulling widening algorithm based on adaptive beamforming, and mainly finished the following work:(1) For the situation that the disturbance and desired signals coherence, this paper proposes a beamforming nulling widening algorithm based on coherent interference. The algorithm can not only effectively eliminate the coherence of the interference signal and the desired signal, but also can broaden the null forming from the interference. The simulation results show that, the algorithm can still make the output performance of beam shaper better, and effectively enhance the robustness of the system, under the condition of the coherent interference environment and the Interference disturbance.(2) For the situation that the co variance matrix tapering will reduce the depth of null with nulling widening, this paper proposes a beamforming nulling widening algorithm based on remodeling of co variance matrix tapering. Through extending the space region of spatial spectral function and controlling the null in depth by depth coefficient, the algorithm not only broadens null, but also deepens the null in depth. The simulation results show that, the algorithm which can better suppress the interference signal, can be used in fewer samplings.(3) This paper puts forward a beamforming nulling widening algorithm combined with projection transformation and diagonal loading based on the minimum variance distortionless response. The algorithm preprocesses the matrix of array receiving data by using the projection transformation matrix of array, and determine the load factor according to the relationship between the load factor and the sampling covariance matrix. The algorithm not only widens the null in width, but also deepens the null in depth. The simulation results show that, this algorithm which can still keep good output performance in the situation of angle interference signal mismatch, can work in fewer samplings steadily.