| In this paper, two different EM numerical methods are applied to analyze the far field radiation properties and the impedance characteristics of the Koch fractal antenna and the Sierpinski carpet fractal microstrip antenna. Firstly, the Method of Moment is used to study two kinds of Koch fractal antennas: one is vertically mounted on the grounded-plane and the other is placed in parallel with the grounded-plane. The current distribution, radiation pattern and input admittance are calculated for the different fractal order and height of Koch fractal antenna placed in parallel with the grounded-plane. Then, the Domain Decomposition FDTD method is developed to calculate the reflectance of the Sierpinski carpet antenna with coaxial probe feed Furthermore, the reflectance of coaxial-patch-feeding EM coupled patch antenna is also calculated The results demonstrate that this kind of antenna can widen the working band The Domain Decomposition FDTD method integrates the use of conformal grids and rectangular grids. In the coaxial line region, circular cylindrical coordinate grids are used instead of the classical staircasing method. In other regions and boundaries, rectangular grids are used. This greatly increases the calculation efficiency. The conclusion has been reached that the multiband property of the Sierpinski carpet fractal microstrip antenna lies on the high orders harmonic model of the main patch of coaxial feeding, not on the fractal structure.
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