| The contemporary international situation accompanied with frequent border disputes is unpredictable.As an important field of electronic countermeasure,electronic reconnaissance plays an irreplaceable role in the field of First Look and First Shoot.To adapt to the complex and changeable battlefield environment,the portable and easy to hide backpack DF(direction finding)system has emerged.However,in the backpack environment,the human body has a certain influence on the performance of the antenna.That influence can decline direction finding accuracy of the DF system.Also,there may be problems such as the error of direction-finding algorithms due to coherent signals.This thesis aimed at improving the direction-finding performance of a DF system in backpack environment.Firstly,research on the influence of human body on antenna performance is conducted.Secondly,improving algorithms to make direction finding accuracy of the DF system better is focused on,to adapt DF system to the backpack environment.The specific research content is as follows:Firstly,in order to improve the performance of finding the direction of single signals,research on the influence of human body on the performance of the backpack DF system is conducted.Then,a better performing adjacent amplitude comparison method combined with the phase comparison method is used for direction finding calculation.Furthermore,based on the study of the influence of human body on antenna performance,the Modified Amplitude & Phase Comparison Method is proposed to address the impact of backpack environment.Finally,simulation analysis is conducted on the Modified Amplitude & Phase Comparison Method in the case of joint multiple array elements.The simulation results show that its performance meets the requirements of the target(RMSE <4°).Secondly,in order to improve the performance of finding the direction of multiple signals,research on various influences on the MUSIC algorithm under backloading environments is conducted.Considered influences include effects of the antenna gain changes,the coherent signals,and the excessive signal to noise ratio differences.Simultaneously corresponding solutions are studied.In order to reduce the amount of computation and improve the computational speed,the equivalent circular array signal model of the antenna is converted into the invented uniform linear array.Then,the Comprehensive Optimized MUSIC algorithm adapted to the backpack environment is proposed to comprehensively address various problems that may exist in the backpack environment.Finally,simulation analysis is conducted on the MUSIC algorithm for comprehensive optimization in the backpack environment.The simulation results show that its performance meets the requirements of the target(RMSE <5°).Finally,using software radio platform based on GNU Radio and USRP to build a DF system in the backpack environment,experiments are conducted to verify the Amplitude & Phase Comparison Method and the Comprehensive Optimized MUSIC algorithm.The results show that both the Amplitude & Phase Comparison Method and the Comprehensive Optimized MUSIC algorithm can meet the performance requirements in the backpack environment,and the Comprehensive Optimized MUSIC algorithm can cope with the problem of coherent signals and the excessive SNR(signal to noise ratio)differences.Based on the above research,aimed at the backpack environment,this article proposes the Modified Amplitude & Phase Comparison Method for single targets and the Comprehensive Optimized MUSIC algorithm for multiple targets.The feasibility and effectiveness of the two algorithms were verified through simulation. |
