This paper describes a microstrip-fed planar monopole antenna using Defected Ground Structure (DGS) technique. In addition, we have applied partial technique in the rectangular radiating element to achieve an ultra wide band characteristic for impedance matching. The simulated impedance band width of this antenna for S11 ≤ -10dB is about 6GHz, from 3.9GHz up to 10.8GHz. The proposed antenna's performance approximately covers the band width of ultra wide band as defined by FCC. Additional features that make this antenna attractive and viable for modern ultra-wideband system applications are its simple configuration, low profile, compactness, and low fabrication cost.