| In the EMC, it is very important to investigate various problem of electromagnetic waves. There are several kinds of analysis algorithms, such as uniform geometrical theory of diffraction (UTD), Finite-difference time-domain (FDTD) method, method of moment (MoM) which can be applied to deal with scattering problems of objects in the presence of electromagnetic waves. When the structures of objects are very complex, it is difficult to find accurate analytical solution, while numerical algorithm can be used to study scattering problem of complex structures.To characterize electromagnetic effects in a complex electromagnetic environment, it is necessary to develop highly accurate and efficient numerical algorithms. Therefore, in this dissertation, conformal FDTD (CFDTD) and FDTD (2,4) methods are further studied with their numerical dispersion error decreased. On the other hand, varieties of two-dimensional and three-dimensional wedges with different materials are studied, and their scattering, reflection and diffraction characteristics are examined. The contribution of this dissertation is given as follows.(1) The equations of conformal FDTD method for handling perfectly electrical conductors (PECs) and dielectrics are given. The generation process of FDTD cells including conformal ones is introduced. Numerical dispersion error in the conventional FDTD is outlined. Then, an improved conformal FDTD algorithm is developed with low-cost, and it is based on a coefficient modification method.(2) Fundamental principles of high order FDTD method are introduced. The equations of FDTD (2,4) compatible conformal FDTD for handling PECs and dielectrics are given. The FDTD (2,4) compatible convolutional perfectly matched layer (CPML) is investigated. Then a low cost coefficient modification technology is introduced into FDTD (2,4) conformal method, which can decrease numerical dispersion error of the algorithm.(3) Scattering problems of wedges under illumination of plane electromagnetic waves and line sources are analyzed, with several high frequency approximation (HFA) solutions given. A multistep method based on FDTD to extract diffraction fields is introduced, which can be used with the improved FDTD algorithms developed in this dissertation.(4) The improved hybrid FDTD algorithms are applied to simulation of two dimensional and three dimensional wedges under illumination of electromagnetic pulses. Scattering and diffraction phenomena of wedges interacting with different electromagnetic pulses are discussed. Amultistep method to extract diffraction fields around the tip of a PEC wedge is used with the improved hybrid FDTD algorithms developed in this dissertation, then the results are compared to the ones of conventional FDTD method, conformal FDTD, and UTD, which proves that the new FDTD algorithms developed in this dissertation have higher accuracy in simulation of two dimensional and three dimensional wedges. Wedges composed of PECs and dielectrics are modeled. A hybrid FDTD algorithm which has conformal cells on the surfaces of both PECs and dielectrics is developed, with its numerical dispersion error decreased. The new hybrid FDTD algorithm is used to analyze the fields around composed wedges in both TE and TM cases, with the wedges illuminated under line sources. The fields are recorded during the simulation, and then FFT and normalization process is done. The normalized fields are compared to the ones of analytical algorithm, which proves that the new hybrid FDTD method can be applied to simulate the scattering process of varieties of composed wedges accurately.(5) FDTD modeling method of antennas is studied. The Gap feed source technique and antenna coaxial feed technique is introduced. The feed techniques and the new hybrid FDTD method are combined and applied to simulate several common antennas. Response modes of different antennas with electromagnetic pulses are achieved, they can be applied to electromagnetic protection deisgn.
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