Characterized by its wide impedance bandwidth and relatively stable radiation pattern, the bow-tie antenna has been widely utilized in the microwave as a suitable radiator. However, the comparatively limited radiation gain will constrain this type of antenna from more extensive applications when higher gain is required. In this paper, a bow-tie antenna etched with modified Sierpinski fractal patterns is proposed, which can enlarge the current path for radiation thus minimize the overall dimensions of the radiator to further increase its impedance bandwidth. Moreover, for the sake of gain-enhancement, an artificial structure consisting of zero- index metamaterials (ZIM) unit is carefully designed and adopted in the fractal pattern etched antenna.