| dc.description.abstract | In this dissertation, based on electromagnetics theory, a complete link between the echo signal of synthetic aperture radar (SAR) and imaging processing is established. Inspired by the method of moment (MoM), which has high theoretical accuracy in computational electromagnetic analysis methods, a SAR raw data simulator based on the MoM is different from the conventional point-target model, which is simply a pure mathematical model. Using Maxwell’s equations and boundary conditions, the electromagnetic wave integral equations are derived to formulate electromagnetic characteristics involving the interaction between metallic and dielectric objects. The simultaneous discretization of the integral equations and surfaces using a set of basis and testing functions defined with triangles leads to dense matrix equations. To accelerate the calculation of large dense matrix equations, they are solved iteratively via the multilevel fast multipole algorithm (MLFMA). After computing the equivalent current density, the scattering field can be integrated over the antenna-illuminated area. By utilizing the synthetic aperture process within different positions, echo data can be generated. In addition, fully polarized echo data can be acquired by changing the polarization of the transmitting and receiving antennas. The fully polarized focus SAR image can be obtained by the refined Omega-K algorithm. The results can be utilized to discuss the scattering mechanism, evaluate the effects of multipath, validate the system performance, and investigate the polarization information.
The proposed method successfully demonstrates comparisons of the simulation results for different materials, interactions between objects, and between monostatic and bistatic systems, and the results at different bandwidths. Different dielectric constant materials, such as Teflon, ceramics glaze (CG) and gallium arsenide (GaAs) are utilized to present the abilities of different scattering characteristics in the focus images. By varying the spacing between two targets, the different degrees of interaction are presented. The effects of scattering characteristics and imaging properties under different bandwidths are investigated. The scattering behaviors between monostatic and bistatic systems are discussed in several cases. Through polarization changes in transmission and receiving antennas with the proposed method, fully polarimetric SAR images can be generated. These data can be used for a comparison with the polarization decomposition method and for error analysis. To validate the effectiveness and performance of the proposed method, a set of measurements was obtained in an anechoic chamber. A network analyzer and a motion controller synchronized by a personal computer were utilized to acquire the echo data and the position vector simultaneously. Then, applying the imaging algorithm to the raw data, the final focus images were obtained. The results from the full-wave method compare well with the experimental results, which successfully demonstrates the reliability of the proposed method.
In conclusion, the simulation of SAR imags based on the MoM and the refined Omega-K algorithm offers more complete recovery of scattering information. The proposed method is useful in designing future novel SAR systems and the analysis of the electromagnetic characteristics of different observation targets. | en_US |