A portable, low-cost, simple monopole antenna is designed, fabricated, and tested, and measured results compared with simulations. Dual-band characteristics at 2.0-2.6 GHz and 3.1-10.6 GHz are obtained by semi-annular shaped radiation patch. Band-notched features at 2.0-3.0 GHz and 5.15-5.825 GHz obtained by providing L-shape slots, rectangular slots in ground plane, and a small ring slot on semi-annular shaped radiation patch, improve the band-notch characteristics which effect the bandwidth of resonant frequencies. The monopole ultra wide band (UWB) antenna was built on an FR4 substrate with a dielectric constant of 4.4 and a size of 50 mm × 24 mm × 1.6 mm. The 3D high-frequency (EM) simulation software (HFSS) is used to simulate and optimize the proposed antenna structure. The measured results of the designed antenna with different dimensions of slots have produced S11 < -10 dB over the three bands (2.0-2.6 GHz, 3.1-5.15 GHz, and 5.8-11.4 GHz) without a circular slot, by adjusting a circular slot radius on a semi-annular structure that improves the band-notch characteristics. The monopole UWB antenna exhibits stable gain and provides omnidirectional radiation pattern over the desired bands.