Study Of Imaging Algorithm Of Synthetic Aperture Radar In THz Band

The technology of Terahertz(THz) is developing rapidly nowadays. Compared with the traditional microwave radar, the wave of THz is shorter, which facilitates the generation of signal with large bandwidth and achieve high resolution. The THz radar has good advantages in micro-target detection and super resolution of imaging. The basic theory of the synthetic aperture radar imaging in THz band is the same as which in microwave band,and THz has the better performance, it is easier to get higher resolution of range direction and azimuth direction for THz radar, for the reason that LFM signal with wider bandwidth is easier to get.As we all know, synthetic aperture radar requires a high stability of radar platform. Actually, for the existence of airflow, engine vibration, synthetic aperture radar imaging platform have the problem of high frequency vibration. The amplitude is small compared with the wavelength in the microwave band, and the impact to the phase is negligible. However, in the THz band, the platform high frequency vibration amplitude is similar to the wavelength, even greater than the wavelength. Therefore, the impact on the phase has to be taken into account. We have done a lot in-depth study base of the problem.Work in this paper is mainly reflected in the following aspects:(1) Range-Doppler algorithm for THz band. At first we derived Range-Doppler algorithm, then we simulated point target and multi-target with this algorithm in THz band, which verified that the RD algorithm is equally applicable to THz band. These work provide foundation for our next study.(2) Modeling high frequency vibration of platform in THz band SAR imaging. When the SAR system is working, high-frequency vibration of platform exists inevitably. Firstly, we made a brief presentation of the high-frequency vibrations, which included definition of it and the reason for its existence. Then based on R-D algorithm we proposed two modeling methods, and deduced them respectively, concluded the effects of high-frequency vibration of platform for SAR imaging. In the microwave band, the wavelength is much bigger than the amplitude, and the effect of high-frequency vibration of platform can be ignored, but in the THz band, the wavelength is shorter, the impact of high-frequency vibration of platform can not be ignored. This paper also gives the three parameters(amplitude, frequency and phase) of high-frequency vibration of platform. Finally, the simulation of point target and multi-target proved these conclusions.(3) The compensation of THz SAR imaging based on the discrete sinusoid frequency modulation transform(DSFMT). In this paper, we study the discrete sinusoid frequency modulation transform deeply, we analysis the effectiveness of the conversion in signal parameter estimation, and the simulation proved it. We proposed the compensation method of the THz SAR imaging based on DSFMT. Finally, the simulation results show the effectiveness of this approach, and analyzes its limitations.(4) the compensation of THz SAR imaging based on Chirplet Decomposition. First, we introduce the theory of Chirplet Decomposition and the existing adaptive Chirplet Decomposition method, and then made the adaptive Chirplet decomposition of a SFM signal. Simulation results show that: the WVD of the decomposition of a SFM signal is similar to the WVD of the original signal. Therefore, we proposed the compensation method for the THz SAR imaging, and the simulation proved the effectiveness of the method. Compared with method based on DSFMT, this method has better performance and broader applicability.