Direction Finding Technique Research Based On Spatial Optical Beam-Forming Networks

Compared with the conventional beam forming techniques,optical beam forming system has been a research hotspot in the field of electro-optical countermeasure equipment,since it's lightweight,free of electromagnetism interference and has wide instant bandwidth.Spatial optical beam forming network(SOBFN)is a kind of optical beam forming system which is based on heterodyne mixing.It has small size,light weight,and can adjust the phase of the signal continuously.This dissertation focuses on this structure,and studies the signal detection and direction finding technology based on SOBFN.The main research contents of this dissertation are as follows:(1)A narrow band signal model for the spatial optical beam forming network is established.Firstly,introduce the working principles of SOBFN and analyze the beam forming process of the system.The optical array output model of SOBFN is established when narrow band signals arrive.Compare it with the traditional array signal model and analyze their differences briefly.Then,verify the feasibility of the system and the accuracy of the output model by computer simulation.The beam forming performance of SOBFN is also analyzed.(2)A signal detection algorithm based on spatial optical beam forming network is proposed.Signal detection is the premise of the signal direction finding.First of all,analyze the characteristics of the observation model and the system response of SOBFN.A signal detection algorithm based on the covariance matrix of the received data is proposed by using the time invariance of the optical array manifold.Then the detection principle of the algorithm is introduced and the detection threshold is given according to the distribution characteristics of the test statistic.Finally,the detection results of the algorithm are given by the simulation experiments,and the performance of the algorithm is analyzed by Monte Carlo simulation.(3)Narrow band direction finding algorithms for spatial optical beam forming network are studied.According to the amplitude distribution characteristics of the SOBFN signal model,a single signal direction finding method based on amplitude fitting is proposed.The feasibility of this algorithm is verified by simulation experiments and the effect of various parameters on the performance of the algorithm is discussed.When there exit multiple signals with the same frequency arriving simultaneously,propose a new algorithm based on Bayesian sparse reconstruction,which is named as Bayesian-DOA.The noise adaptation ability,the spatial resolution and the performance with small sample data of the algorithm are analyzed through Monte Carlo simulations.(4)The direction finding methods for broadband signal for spatial optical beam forming network are studied.Firstly,decompose the broadband signal into the narrow band data by short time Fourier transform.Then exploit the spatial sparsity of the narrow band data to realize wideband DOA estimation.According to the different processing methods of discrete frequency data,two kinds of wideband direction finding algorithms are proposed: non coherent Bayesian-DOA method and multi-model method.The performance and efficiency of the two algorithms are compared via simulation experiments.