Design tri-band rectangular patch antenna is presented. This paper focuses on designing an antenna that can operate with three bands; 2.4, 3.5 and 4.4GHz, respectively. These bands are accepted by Wi-Fi, WiMAX and WLAN in Military band applications. The shape of the proposed design is based on simple rectangular patches with inset-feed on one surface of the FR4 substrate. On the other surface of FR4 substrate, is the infinite ground plane. Also Computer Simulation Technology (CST) microwave studio 2012 is used for the design of antenna. This design is fabricated using photolithographic process.