A rectangular slot antenna for UWB applications is proposed in this paper. The slot is designed in stepped configuration and is excited by an L-shaped microstrip line flared at the end. The measured impedance bandwidth (¡10 dB) from 3 GHz to 27 GHz is achieved. The radiation patterns are bidirectional in the E plane and omnidirectional in the H plane with the measured peak gain around 5 dBi throughout the band. The experimental results are in good agreement with the simulated results. A detail parametric study is done for the flare angle and the flare width to axis ratio and their effect on the impedance bandwidth and the reflection coeffcient is described.