Research On Virtual Aperture For Shipborne High Frequency Surface Wave Radar

Shipborne High Frequency Surface Wave Radar works in the 3-30 MHz,Its working wavelength is dozens to hundred meters.By using the diffraction effect of long waves along the Earth's surface,radar can detect targets beyond visual range.However,due to the limitation of the platform,the array's aperture of the Shipborne High Frequency Surface Wave Radar is small,and its beam width is too wide,so the azimuth resolution of the real array is poor.Besides,because of the movement of the ship,the Bragg peak of the first-order sea clutter broads to flood a large number of low-speed targets in the Doppler spectrum,it makes the target detection difficult.The focus of this paper is to research how to construct a virtual array which is much larger than the real array by using the movement of array in the first-order sea clutter background,then use the narrow beam of the virtual array and the accumulation effect of the virtual element to improve azimuth estimation accuracy and azimuth resolutionIn the signal processing of Shipborne High Frequency Surface Wave Radar,it is necessary to suppress the first-order sea clutter,this paper has some research on the suppression of first-order sea clutter by using the Orthogonal Projection Algorithm and the Oblique Projection Algorithm.Firstly,we analyze the suppression principle of the projection algorithm.Secondly,we make an improvement to improve the suppression effect at the Doppler widening boundary of the sea clutter.Finally,the two suppression algorithms are compared and their inhibitory effects when the first order Bragg frequency offset are analyzed.As to the problem of first order Bragg frequency offset,this paper proposes a clutter suppression method based on first order Bragg frequency estimation.The results of computer simulation show that the Improved Orthogonal Projection Algorithm and the Improved Oblique Projection Algorithm can suppress the sea clutter at the widening boundary.The Oblique Projection Algorithm has a good effect when the sea clutter's direction is in the target's main lobe.However,when the actual Bragg frequency of first-order sea clutter shift,the suppression effect of the Oblique Projection Algorithm decreases rapidly,but the Orthogonal Projection Algorithm can maintain its inhibitory performance in the limited deviation interval.And the clutter suppression method based on Bragg frequency estimation can improve the effect of sea clutter suppression when the first order Bragg frequency offset.The virtual aperture method of Shipborne High Frequency Surface Wave Radar is based on the suppression of sea clutter,taking use of the movement of high-frequency surface wave radar's array to form an equivalent virtual array.By using the narrow Beam of large aperture virtual array,we can get the direction of target's azimuth and achieve highly azimuth resolution.In this paper,two vitual aperture algorithms are proposed,which called Time Phase Compensation Algorithm and Overlapping Antenna Correlation Algorithm,and Overlapping Overlapping Antenna Algorithm is studied emphatically between them.Firstly,the Overlapping Antenna Correlation Algorithm is proposed in the form of Shipborne High Frequency Surface Wave Radar.Secondly,the algorithm is improved by cubic spline interpolation and singular value elimination to improve the estimation accuracy of Correlation Factor.thirdly the performance analysis of the algorithm and the influence of the array's irregular movement is given.Then,the Overlapping Antenna Correlation Algorithm based on orthogonal projection and the Overlapping Antenna Correlation Algorithm based on oblique projection are studied.Finally,the advantages and disadvantages of the algorithms are analyzed.The results of computer simulation show that the Overlapping Antenna Correlation Algorithm based on sea clutter suppression can obtain a higher resolution than the real array.And it can avoid the splitting of main lobe which will appear when using orthogonal projection algorithm to suppress the sea clutter in targets' main lobe,so we can obtain an accurate drection of azimuth estimation.