A microstrip line fed dual band-reject ultra wideband antenna with sharp band edge frequency of 3.1-10.6 GHz is presented. The antenna consists of a rectangular patch on the front side and a partial ground plane at the rear. A step is cut on the bottom edge of the patch for impedance matching. A split ring slot etched on the radiating patch rejects WiMAX (3.3-3.8 GHz) band, and a pair of inverted S-shaped slot in the partial ground plane rejects WLAN (5-6 GHz) band. In order to eliminate the radiation outside the FCC specified 3.1-10.6 GHz band, a rectangular slot is etched on the ground plane below the feed line. The antenna exhibits UWB band width of 109% except for the notch band. The radiation characteristics are consistent throughout the band. The performance of the antenna is analyzed both in the frequency domain and time domain to assess its suitability for ultra wideband communication. Pulse distortion of the antenna is investigated for both Rayleigh and Gaussian source pulse excitation.