The monopole antenna using a simple architecture for WLAN 2.4 GHz and using a 50-ohm mini coaxial cable is proposed and investigated. Using an extended strip on a longest path of the antenna is to resonate a 2.4GHz mode and a mode about 5.8GHz. By an introduction of a pair of L-shaped strips on the antenna to help the impedance match. The antenna is designed with a simple structure, and a compact size of 35 × 12 mm 2 . Obtained bandwidth of the antenna meets the bands of WLAN (2.4 -2.484 GHz, 5.15 -5.35 GHz and 5.725 -5.825 GHz) and WiMAX (3.4 -3.7 GHz and 5.25 -5.85 GHz). The simulated radiation patterns are omni-directional, which is suitable for USB device applications.