| Terahertz waves usually refer to electromagnetic waves with frequencies between 0.1-10 THz. The terahertz band lies between the millimeter wave and infrared, which is a transitory band from electronics to photonics. The special spectral position decides that terahertz waves have special properties and applications differing from other bands. With the breakthrough in terahertz sources, signal detectors and other devices, the terahertz radar technology develops rapidly, and many terahertz radar systems have been established both at home and abroad, mainly for use of the study of high resolution imaging for the stationary targets and turntable targets. However, research on micro-motion targets, as a common type of objects in the real world, is still very limited. Also, micro-motion in terahertz band has some special characteristics different with them in the microwave band, which makes the traditional methods inapplicably. We researched in detailed the characteristics of micro-motion in terahertz band in this dissertation, and proposed the parameter estimation algorithms and high resolution imaging methods with terahertz radar.We introduced the background and significance of this research, the related works and works to be done in the areas of micro-motion modeling, feature extraction, imaging and micro-motion researches in terahertz band in Chapter 1, and summarized the basic methodologies, techniques, as well as the main problems to be solved. The major work is summed up at the end of this chapter.In Chapter 2, we researched in depth a Doppler aliasing free micro-motion parameter estimation algorithm based on the spliced time-frequency image. We firstly analyzed the radar echo models of micro-motion targets and reached a conclusion that the micro-Doppler of micro-motion target is sine modulated, and then proposed a Doppler aliasing free micro-motion parameter estimation algorithm based on time-frequency image spliced and inverse Radon transform, and then the detailed instructions were put forward. Finally, we verified the feasibility and high accuracy of this algorithm through simulation, and analyzed its anti-noise performance.In Chapter 3, we researched in depth a Doppler aliasing algorithm for estimating free micro-motion parameters based on the modulo Generalized Hough transform. We confirmed the scope of application of the algorithm in Chapter 2, and pointed out the root of its invalidation in high precession angle cases. Thereafter, we proposed the sliding scattering center model, and analyzed the sliding characteristics of precessing cone. Then the algorithm was proposed based on these characteristics and the high estimation precision and robust anti-noise performance are verified through simulation experiments.In Chapter 4, we introduced two traditional imaging methods for micro-motion target with FMCW. We firstly analyzed the ISAR imaging with FMCW for turntable targets, and then the ISAR imaging based on the compensation of translation and the ISAR imaging based on the micro-motion angle for micro-motion targets were proposed. The imaging theories were verified by the simulation and CST data.In Chapter 5, we introduced an Azimuth-Elevation imaging method based on the sparse Bayesian theory in terahertz band for micro-motion targets. It combined the Compressed Sensing and high resolution imaging and the results of simulation are acceptable as well. We firstly gave a detailed account of the Compressed Sensing theory and the sparse representation model of Azimuth-Elevation imaging method, and then verified the good performance of this method through simulation and CST data. The 2D imaging results of a precession missile model were shown at the end.Finally, we concluded the research and the main innovative contributions of this dissertation, and then talked about the tendency in micro-motion target research in terahertz band and the problems to be solved, as well as the research directions and problems should be concerned in the future. |
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