Research On Inverse Synthetic Aperture Radar Fine Imaging Technology Of Aerospace Targets

Inverse synthetic aperture radar(ISAR)imaging,which is able to generate the 1D,2D and even 3D image of a noncooperative target,plays an important role in aerospace target surveillance.The resolution of the image is inversely proportional to the bandwidth of the radar.Due to the limited bandwidth,the desired high-resolution image cannot be achieved with the currently available wideband radar.To improve the resolution,the fine imaging methods of aerospace targets are studied to support the aerospace target surveillance of our country.In chapter 1,the background and significance of the research are first introduced.Then,the development and application of typical ISAR systems are reviewed,and the research status of high-resolution ISAR imaging technology is analyzed.Finally,the main contents of the dissertation are summarized.In chapter 2,the ISAR imaging principle is introduced.The range-Doppler imaging algorithm is first described,followed by the fine imaging flowchart of aerospace target.Then,the imaging technologies of some key procedures in the flowchart are summarized.Finally,the typical image quality indicators are introduced.In chapter 3,the problem of compensating the wideband echo is discussed.For the amplitude-phase distortion of wideband radar,its influence on ISAR imaging is re-analyzed and an adaptive framework based on cross-range profiles is proposed to simplify the compensation procedure.As for the range alignment,the effect of migration through resolution cell(MTRC)on range alignment is analyzed.Taking MTRC into account,a robust range alignment algorithm based on the minimum entropy criterion is proposed,which effectively improves the performance under MTRC.In chapter 4,the problem of high-resolution imaging in the range dimension is discussed.To improve the range resolution,the sparse subband ISAR imaging model is established and a novel framework based on the autoregressive model and the smoothed?~0 algorithm is proposed.The proposed framework is robust to the band gap and noise,and the fusion image is satisfactory.To provide more information about the target,the scattering model based on geometrical theory of diffraction is established.The parameters of each scattering center are estimated via iterative adaptive approach(IAA),which enriches the target characteristic information.In chapter 5,the problem of high-resolution imaging in the cross-range dimension is discussed.For three-axis-stabilized space-orbit-targets,the rotational parameters are calculated according to the radar line of sight,and the range-compressed signal is resampled to eliminate the influence of the non-uniform rotation of the target,thereby realizing high-resolution imaging with a large angle.For maneuvering targets,the optimal coherent processing interval is first selected.IAA is then used to perform the azimuth compression,generating a high-resolution image with a small angle.At the end of the dissertation,the work is summarized and the future work is discussed.