Research On Beam-forming Method Of Distributed Coherent Array

With the development of radar detection technology,requirements for radar detection power,accuracy and resolution are also increasing.However,the airborne radar is limited by many factors such as platform volume and load capacity,and the diameter power product cannot increase indefinitely,so there is a bottleneck in improving radar's performance.This bottleneck can be overcome by using distributed coherent radar.The improvement of detection power can be achieved by increasing the number of drones.It has the advantages of low cost,strong battlefield survivability and high spatial resolution,but the distributed system also has some drawbacks.The sparse arrangement of the antennas can cause a more serious grating lobe problem,which is very disadvantageous for the non-fuzzy estimation of targets,the suppression of clutter and interference.Aiming at the above problems,an algorithm is proposed to solve the spatial blur by using multiple carrier frequencies,which is suitable for the non-interference situation and can solve the target direction more accurately.Then this thesis discusses the presence of interference.A set of carrier frequencies are designed such that all angles other than the target angle are not at the position of grating lobe in at least two of the patterns.Estimated the angle of the target is realized by combining the spatial filtering with the AMF detector.The main work of this thesis is summarized as follows: 1.Position of distributed coherent array is optimized based on genetic algorithm.Two kinds of methods on sparse array optimization are introduced,which are synthetic class method and global optimization random search method.This thesis mainly studies the genetic algorithm.Firstly,biological basis,basic idea and processing step of genetic algorithm are introduced.Then position of the thinned linear array,sparse circular array,distributed array and airborne distributed array are optimized by genetic algorithm.The goal of optimization is to reduce the side lobes of the antenna pattern function as much as possible when the number of array elements and the aperture size are determined.Finally,the differences of performance between the optimized array and the uniform sparse array are compared by simulation.2.A distributed coherent array design method for search tasks is studied.The main idea is searching for multiple directions simultaneously by using grating lobes.This can improve the search efficiency and the energy utilization rate of the transmitted signal.Aiming at the problem of spatial blur in target detection,analogous to the method of solving distance blur by using different pulse repetition interval,a method is proposed to solve spatial blur by using multiple sets of different distances between array elements or transmitting signal wavelengths.The performance of the algorithm in the noise background is analyzed by simulation.In addition,a position matching algorithm in near-field mode is studied.3.The algorithm of estimating the position of target in the presence of interference is studied.When the uniform sparse array works in different frequencies,the frequencies of the transmitted signals are designed by genetic algorithm,such that all angles other than the target angle are not at the position of grating lobe in at least two of the patterns.Then do FA processing on the received data,based on the processing result,the AMF detector is used to get the location of the target.