| High-frequency(HF)radar works in the range of 3MHz to 30 MHz.By using the characteristics of vertically polarized electromagnetic wave diffraction propagation along the ocean surface,it realizes all-weather and beyond visual range monitoring of ocean surface dynamic parameters and targets.This is of great significance to ocean resource observation and national ocean security.HF radar system can be divided into array HF radar and compact HF radar.The compact high frequency surface wave radar(HFSWR)uses a monopole crosswise as the receiving antenna.Compared with the array HF radar system,the system has the advantages of low cost,small size,easy erection and maintenance.Its ability to observe the ocean surface is widely recognized.Direction finding accuracy of compact HFSWR has been the focus of research for decades.Due to the influence of its own system,the direction finding accuracy of compact HFSWR is often not ideal.There are two main reasons.First,there is distortion in the antenna pattern.Affected by electromagnetic interference in the experimental environment,there is error between the measured antenna pattern and the actual antenna pattern.Secondly,the spacing of the compact HFSWR array is small,which affects the angle estimation accuracy.In view of the above two problems,the main research work of this thesis is as follows1)Through theoretical derivation and experimental simulation,the influence of measurement error on angle estimation accuracy is analyzed when there is an error between measured and actual direction chart under ideal conditions.Then,the relationship between angle estimation accuracy and measurement error and distortion factor is analyzed.According to the experimental results,an interpolation smoothing method of distorted direction graph is proposed.The angle of arrival estimation based on the interpolation direction graph has higher Angle estimation accuracy and flow field inversion effect.2)This thesis studies the angle estimation accuracy of compact HF antenna array with small size.According to the mechanism of ormia ochracea coupling auditory system amplifying the phase difference between two ears,and using the equivalent circuit model of coupled auditory system,the ormia ochracea coupling auditory system is proposed to estimate the angle of arrival of small high frequency antenna array.In this method,the coupling system is used to adjust the orientation vector of the antenna array,and the phase difference of the received signal between different channels containing the information of the arrival angle of the incoming signal is amplified.Finally,the arrival angle is estimated by the multiple signal classification algorithm(MUSIC).3)The azimuth estimation capability of compact binary cross-loop/monopole antenna array is studied.The traditional MUSIC algorithm and the improved MUSIC algorithm of ormia ochracea coupling system are used to simulate the azimuth estimation ability of compact binary array.Through the analysis of the root mean square error of angle estimation and angle resolution,It is verified that the improved MUSIC algorithm of ormia ochracea coupling system has higher accuracy than the traditional MUSIC algorithm.4)The pitching angle estimation ability of the compact vertical binary crossloop/monopole antenna array is studied.After the radar data are corrected by the high energy spectral points in the first-order peak region,the pitch Angle estimation results of the vertical binary array are simulated by using the two algorithms.The simulation results shows that the MUSIC algorithm angle estimation based on the Ormia ochracea coupling system has higher angle estimation accuracy by using the vertical binary cross-loop/monopole antenna array.Under the condition of 10 d B signal to noise ratio,the root mean square error of angle estimation is 2° lower than that of traditional MUSIC algorithm,and the angle estimation accuracy is improved by about 55%,which verifies the feasibility of this method in small antenna array direction finding. |
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