The spectral congestion in existing Industrial, Scientific, and Medical (ISM) Wireless Local Area Network (WLAN) bands has led to the emergence of new ISM bands (Unlicensed National Information Infrastructure (UNII)) from 5.150 to 5.710 GHz. In this paper, a simple uniplanar, high gain, microstrip antenna is designed, fabricated, and tested for existing WLAN and new UNII standards. The proposed antenna provides dualband operation by joining two rectangular rings and cutting Defected Ground Structure in the Coplanar Wave Guide (CPW) feed. The experimental and simulation results show good return loss characteristics and stable radiation pattern over the desired frequency bands ranging from 2.20 to 2.65 GHz (WLAN band) at a lower frequency and from 5.0 to 5.45 GHz (UNII-1/UNII-2 bands). The measured peak gains are 5.5 and 4.9 dBi at 2.45 GHz (WLAN band) and 5.15 GHz (UNII band), respectively.