Research And Implementation Of Dual Channel Direction Finding System Based On Correlation Interferometer

With the rapid development of radio communication technology,wireless applications have rapidly developed with its ubiquitous convenience and become an important part of information consumption.However,radio interference is also increasing.The new types of fraud in the private radio stations,especially the "pseudo base station" and "black radio",are very harmful.It not only disturbing the normal broadcasting order,but also easy to communicate with the civil aviation.Radio monitoring is the use of electronic equipment to search for,intercept and analyze radio signals,and use radio direction finding technology to locate the transmitting station.This dissertation takes the radio direction finding technology as the research content,and focuses on the research of the phase interferometer direction finding technology,the cross-spectrum measurement phase difference,the relative interferometer direction finding technology,the hardware and software algorithms of the dual-channel direction finding system.Therefore,the main research content of this dissertation includes the following sections.Firstly,it introduces and analyzes the principles and characteristics of common radio direction finding systems,including amplitude comparison type direction finding system,Doppler direction finding system,arrival time difference direction finding system,spatial spectrum estimation direction finding system,and focuses on the phase.The principle of the interferometer's direction finding system is analyzed,and its DF error is analyzed.When the array element's baseline length is greater than half the wavelength,multi-valued ambiguity will occur.But the variance of the error is inversely proportional to the square of the antenna element's baseline length.So it is contradictory phenomena.Then it discusses the correction of channel amplitude inconsistency in dual-channel direction finding system,analyzes the factors influencing channel amplitude and phase inconsistency,and introduces two correction methods,LMS adaptive algorithm and RLS adaptive algorithm.Secondly,the cross-spectral method to find the phase difference method and its optimization algorithm are studied.In the dual-channel direction finding system,the phase of the cross-spectral density function of the two signals at the frequency is the phase difference of the two signals at the frequency component.Based on the cross spectrum method of broadband signal,the phase difference at each frequency component in the bandwidth is analyzed,and the cumulative average is carried out.The time complexity of the algorithm is increased while the accuracy of the phase difference is increased,and the timeliness of the direction finding system is reduced.In order to improve the efficiency of measuring phase difference,a cross-spectrum method based on sparse fast Fourier transform is proposed.The time complexity of the improved algorithm is analyzed,and the performance of the improved algorithm is simulated and analyzed.Then,the basic principle of the correlation interferometer direction finding and its improved algorithm are mainly discussed.The relative interferometer direction finding uses the phase difference information of the actual received signal to correlate with the data of the sample library to obtain the azimuth information of the incident signal.The minimum aperture is limited and avoiding complex phase deblurring calculations.However,the frequency,azimuth and pitch angles in the phase difference sample database are all discrete,which can not guarantee the exact match between the frequency and angle of the sample database data and the actual signal.Therefore,a method of establishing a phase difference sample library based on the guide baseline is proposed and established in real time.The phase difference sample library reduces the size of the sample library and solves the problem that the frequency and angle cannot be completely matched.Finally,the hardware module and software flow of the dual-channel direction finding system based on the relevant interferometer are introduced,and the system is adjusted and tested.The system design,function configuration and hardware module design of the system are mainly described,including the digital down conversion processing module,the switch matrix of the antenna array,the control board and the antenna control interface.During the joint debugging and testing of the system,the DF results of different frequency signals were compared and analyzed.