Research On Using Broadened Bragg Peak Spectrum Calibrate Antenna Array Under Complicated Environment

In a shipborne Over-the-Horizon Radar (OTHR) system, the complicated environment of the antenna array will distort the array directional response, which is from different sources, and the distortion will weaken the performance of various super-resolution methods, such as Multiple Signal Classification (MUSIC). Therefore, it is necessary to calibrate the array error response in order to improve the capability and the precision of the bearing estimation. When the ship moves, the velocity bin of the broadened first-order Bragg peak spectrum is corresponding to first-order sea clutter from different directions, so it is reasonable to use velocity bins as calibration sources. Based on the researches of utilizing broadened first-order sea clutter spectrum as calibration source, this thesis studies the non ideality of sea clutter calibration source, and presents a better calibration methods by improving the non ideality of sea clutter.First of all, several factors that could produce the distortion of the directional response of array antenna are analyzed, and the model of directional response function on the background of near extremity scattering under shipborne OTHR is established.Secondly, with the analysis of the principle on spreading the first-order Bragg peak spectrum in shipborne OTHR, and the feasibility of using the broadened first-order sea clutter as the calibration sources, the mathematical model of a calibration source based on first-order sea clutter is established. After that, the non ideality of using first-order sea clutter as calibration sources is discussed, and then the non-point source property, the low signal to noise ratio property and the property of the sea clutter's disordered amplitude are analyzed in detail.This thesis emphasizes the effect of using first-order sea clutter as calibration sources on array signal adjustment. The influence on extracting array directional response error, which is produced by the non-point source and the low signal to noise ratio, is researched when pattern and taking relative directional response error coefficient between array bins into account. Finally, for the non-point source property of the sea clutter, three methods including increasing accumulation frequency modulated periods, raising ship moving velocity and getting more accumulation number of snapshots are proposed. Meanwhile, for the low signal to noise ratio property of sea clutter, a scheme of adjusting and averaging the signal from multiple range gates is proposed. The simulation results indicate that by using the methods proposed in this thesis, sea clutter calibration source can be utilized efficiently under complicated background.