A modified hexagonal Sierpinski gasket-based fractal antenna is proposed for ultrawide-band (UWB) wireless applications. The designed antenna has miniaturized (36 $\times $ 48 mm$^{2})$ and multiband characteristics. Two design guidelines, the partial ground plane technique and the circular annular ring patch on the substrate, are applied to improve impedance matching and radiation pattern characteristics. According to the simulation results, the proposed modified antenna has a reflection coefficient $S_{11} $ of less than --15 dB, a linear phase of the reflection coefficient, 80{\%} radiation efficiency, 2--4.5 dBi antenna gain, and omnidirectional radiation pattern properties over the full UWB spectrum (3.1--10.6 GHz). Simulated results obtained for this antenna show the expected good radiation behavior within the full 7.5-GHz UWB bandwidth.