A Study On DOA Estimation And Constant Beamwidth Beamforming Algorithms Of Wideband Array Signals

As the instantaneous bandwidth required by electronic reconnaissance becomes wider and wider,the requirements for radar signal processing for large bandwidth and high range resolution are increasing,and array processing of wideband signals is receiving increasing attention.Since the array does not satisfy the invariable additivity with respect to wideband signals,the processing method of narrowband signals is no longer suitable for the processing of wideband signals.On this condition,this thesis first studies the direction of arrival(DOA)estimation of wideband signals,and focuses on the wideband beamforming techniques of constant beamwidth and wideband beampattern synthesis.Firstly,two subspace-based wideband DOA estimation algorithms,incoherent signal subspace method(ISSM)and coherent signal subspace algorithm(CSSM)are introduced.The two methods are compared and analyzed.Then the CSSM algorithm which is robust to the prediction angle error is introduced.The idea of this method is to construct the evaluation spectrum function based on the rough estimate angle of the source,and to search the evaluation peak to obtain the final direction of arrival estimation.On the basis of analyzing and comparing its performance,aiming at the problem that the method error is large and the incoherent signal cannot be measured,an improved 2-norm cross detection CSSM algorithm is proposed,which uses the cross characteristics of the original evaluation spectrum to establish a new evaluation spectrum.The function makes the evaluation spectrum energy more concentrated.Compared with the original method,this method can estimate the non-coherent signal and has better angle estimation performance.The simulation results show that the improved algorithm has an estimated error improvement of 0.4° compared with the original method.Then the wideband beamforming method based on space-frequency structure is studied,then the Chebyshev-weighted constant beamwidth wideband beamforming method based on Newton iteration is also introduced.Then,the classical wideband beamforming method based on space-time structure is introduced,and the beamforming weight is generated by the conventional weighted least squares method.For important applications of the beampattern synthesis technology in wideband beamforming,a wideband beamforming method based on iterative variable weighted least squares is introduced.Aiming at the problem that when beamforming main lobe pointing away from the normal direction occurs,the convex high sidelobe level with frequency distortion will affect the beamforming performance,an improved fast iterative least squares beamforming method is proposed.The idea of this method is to change the design of the stop-band weight function and the iterative method to improve the frequency uniformity while improving the flatness of the beamforming while maintaining an approximately constant beamwidth.The simulation results of the equidistant line array show that the proposed method effectively suppresses the distortion of the sidelobe level relative to the original method when the main beam of the beam forming direction deviates from the normal direction.The method is increased minimum first main to main ratio by 16 d B compared with the original one,and the expected beam pattern is obtained,which realizes wideband beampattern synthesis.The wideband direction estimation and wideband beampattern synthesis method proposed in this thesis are expected to be applied to the electronic reconnaissance array system,which provides support for the broadband signal direction finding technology of military and civilian use in our country.