Research On Real-time Direction Finding Technology Of Passive Array In Complex Electromagnetic Environment

Passive array direction finding is to set multiple sensors at different positions in space to form a sensor array,use the array to receive and process the far-field spatial signal,and estimate the arrival angle of the far-field signal according to the geometric configuration of the array,this process is also called array direction of arrival(DOA)estimation,now it has been widely used in many civil and military fields.Taking the complex electromagnetic environment as the background,this paper focuses on the direction finding algorithm of coherent signal and broadband linear frequency modulation signal under uniform circular array.Due to the multipath effect of signals,passive arrays will receive a large number of coherent signals in space.For passive arrays,the signal subspace and noise subspace of coherent signals are intertwined,resulting in rank loss of the correlation matrix output by the array,which makes the traditional algorithm unable to correctly estimate the arrival angle of incoming waves in this case.In this paper,a forward / backward smoothing algorithm based on mode space is proposed under the uniform circular array model.Firstly,the uniform circular array is equivalent to a virtual uniform linear array,and then the data covariance matrix output by the array is reconstructed to make the reconstructed data covariance matrix orthogonal to the signal subspace and noise subspace,so as to complete the decoherence operation of the coherent signal under the circular array.Finally,the spatial spectrum estimation algorithm is used to estimate the angle of arrival of the coherent signal source,Simulation results verify the effectiveness of the algorithm.Because broadband linear frequency modulation(LFM)signal has the advantages of large amount of information and good detection performance,it has been widely used.However,the array flow pattern matrix of broadband signal is time-varying,and the satisfactory direction finding performance can not be achieved when using the traditional DOA estimation algorithm.In this paper,a direction of arrival estimation algorithm based on fractional Fourier transform(FRFT)is proposed under the uniform circular array model.Firstly,a new array model is constructed by using the energy aggregation characteristics of FRFT to LFM signal,and then the array flow pattern matrix under the virtual uniform linear array is obtained by using the circular array mode space algorithm,Thus,the DOA estimation of broadband LFM signal is completed.The algorithm is suitable for uniform circular array and can estimate the two-dimensional angle of arrival of multiple LFM signals.Simulation experiments verify the good performance of the algorithm.