Terahertz Radar’s High-Quality Imaging Method Based On The Overlapping Sub-Aperture

Compared with traditional imaging radar,terahertz radar has the advantages of short wavelength and large bandwidth.And the theoretical resolution of terahertz radar using CSAR(Circular Synthetic Aperture Radar)mode can reach the sub-millimeter level.However,because the terahertz frequency band has the characteristics of particularly strong anisotropy of scattered energy,the traditional CSAR imaging method will cause the problem of low imaging quality.Among them,the target and noise are mixed in the full-aperture imaging result,which is difficult to be used for automatic target recognition.And in the imaging result of the sub-aperture-based imaging method,the edges of the target are still mixed with noise,and serious fake scattering points are produced.Existing research has improved the sub-aperture division method in the traditional sub-aperture-based imaging method,and the improved sub-aperture division method has improved the imaging quality.At present,the basic idea of improvement is to identify strong scattering energy in the echo energy function,and adaptively divide the sub-aperture according to its center position and width.This type of imaging method does not completely solve the problems,edges and noise mixing and fake scattering points,in CSAR imaging of terahertz radar.In addition,this type of imaging method uses the operation of identifying strong scattered energy according to the energy threshold.The unscientific nature of this operation causes this type of imaging method to rely on manual adjustment to achieve the best imaging quality.Terahertz radar’s high-quality imaging method based on the overlapping sub-aperture has been emphatically studied.The main work and results are as follows:1.The principle and key conditions of terahertz radar’s existing CSAR imaging method to improve the imaging quality have been deeply studied,and a terahertz radar’s high-quality imaging method based on sub-aperture has been proposed.After analysis,it is concluded that the key to improve the imaging quality of terahertz radar is to ensure that the sub-aperture is consistent with the persistent angle of the strong scattering energy.In addition,it is also founded that the anisotropy of scattered energy in CSAR imaging,especially terahertz radar imaging,would produce an equivalent narrowing of the sub-aperture.According to this phenomenon,when the two cannot be matched,the sub-aperture should be appropriately wider than the strong scattering energy,so that the imaging quality can be well to the greatest extent.It is considered that it is difficult to accurately identify all the strong scattered energy in a complex shape target.Therefore,a method of dividing overlapping sub-apertures is proposed to improve the imaging quality.Moreover,considering that the strong scattering energy cut off by the sub-aperture will be more likely to generate fake scattering points,a sub-aperture boundary point selection method is proposed to improve the imaging quality.2.The concrete realization of the sub-aperture boundary point selection method has been deeply studied.Existing methods all divide sub-apertures based on echo energy.For the two steps of the sub-aperture boundary point selection method,the alternative sub-aperture boundary point selection method based on the echo correlation coefficient and the strong scattering energy identification method based on the echo energy coefficient of variation are respectively proposed.Among them,the strong scattering energy identification method based on the echo energy coefficient of variation solves the problem that the existing methods rely on manual adjustment.This method has a universal threshold for identifying strong scattering energy to different targets,and it is more in line with the principle of equivalent narrowing of the sub-aperture discovered.