Research On Key Technologies Of DOA Estimation For Uniform Circular Array With Directional Antennas

Direction-of-arrival(DOA)estimation is the key technology in array signal processing.Uniform circular arrays(UCAs)with directional antennas have been widely used in military and civilian fields because of its long detection distance,high system sensitivity and strong anti-interference ability.However,considering the factors of the directionality,the phase center,the polarization,the main lobe and near-ground reflection in real-world scene,there are some technical problems that need to be solved urgently,such as the variable array aperture,the lower signal-to-noise ratio(SNR)received,the higher computational complexity,and the performance degradation of conventional DOA estimation methods in the presence of plane-reflection.This paper focuses on the characteristic parameters of directional antennas and DOA estimation of UCAs with directional antennas.Several main technologies involved in this subject are theoretically studied.The main work of this paper is summarized as follows:(1)A DOA estimation method for polarized signals based on variable phase center is proposed.It aims to address the DOA estimation problem of polarized signals impinging on an inward UCA with uncertain phase centers.Analyzing the far-field phase distribution by means of the propagation model of the inward UCA,an array signal model with polarized signals for the inward UCA is established.The effective working radius is calculated by minimizing phase differences between adjacent antennas within the scope of half power beamwidth(HPBW).The traditional DOA estimation criterion is improved by using the non-zero property of polarized vector and the orthogonality of steering vectors and noise subspace.Using the proposed criterion,DO As can be estimated by searching in spatial domain instead of polarization domain.(2)A low complexity DOA estimation method using reconfigurable sectorized steering vectors is proposed.It is intended to solve the problem of high computational complexity in DOA estimation using all elements of UCAs.Firstly,the azimuth plane is split into multiple angular sectors according to HPBW of antennas,the approximate steering vector is constructed by JacobiAnger series.And the steering vector of any spatial sector is reconstructed by Hadamard cyclic vector with Vandermonde structure.Secondly,the reconfigurable sectorized steering vector is used to construct the dimension-reduced array signal model in an arbitrary spatial sector,and the computational complexity is reduced by diminishing the dimension of the correlation matrix.In this way,the DOA estimation problem on the azimuth plane is transformed into that of multiple spatial sectors,so as to reduce the number of receiving channels of the system.(3)A spatial filtering technology with adjustable gain in the scope of HPBW is proposed,which is completely independent of wave number.It aims to address the problem of DOA estimation for UCAs with directional antennas under lower SNR.By analysing the radiation distribution of continuous excitation in far-field region,an intensity response function is derived.By discretizing its spatial angle and introducing the adjustable gain parameter,a filter matrix is obtained.With the filter matrix,incoming signals are filtered to improve SNR in the expected spatial sector,so as to solve the problem that they fall into the antenna sidelobes or nulls due to the layout of array,main lobe orientation and radiation pattern of directional antennas.The proposed model has the advantages of high estimation accuracy,less number of antennas and high angular resolution under lower SNR.(4)A multi-parameter DOA estimation based on Cramer-Rao bound(CRB)for UCAs with directional antennas is proposed.It aims to address the problem of DOA estimation for UCAs in the presence of plane-reflection.The effect of the near-ground reflection of incoming signals on the far-field radiation characteristics of directional antennas is firstly analyzed,and the parameter of height-to-wavelength ratio(HWR)is introduced.Based on the principle of image reconstruction,a three-dimensional radiation pattern model with horizontal negative image factor is derived.Then,the model is introduced into steering vectors of the signal model for UCAs with directional antennas.And the DOA estimation method with HWR constraint parameter is proposed,which labels the CRB as the cost function.The simulation results show that the DOA estimation method using this proposed model has higher estimation accuracy than those traditional models in the presence of reflected signals.