A horizontally polarized ultra wideband stepped slot antenna is proposed in this paper. First, a stepped-slot structure is fed by an L shaped microstrip feed to achieve multiple resonances. Then a parasitic slot is introduced near the vertical arm of the L-shaped feed to get better impedance matching over the bandwidth of 3.7 GHz (5.0-8.7 GHz). Further, an impedance step is introduced in the feed line and the measured-10 dB impedance bandwidth covering from 2.8 to 12.8 GHz is achieved. The measured peak gain is around 4.5 dBi throughout the band. The measured radiation patterns are bidirectional in E plane and omnidirectional in H plane. The experimental results are in close agreement with the simulated results. This antenna can be used for ultra-wideband communication devices, medical imaging and vehicular radars.