The development of wireless communication technologies widely using microstrip antenna , has attracted much attention in recent years. In wireless communication, Microstrip antenna is important device for communication above 1 GHz. It is used in mobile communication, aircraft and satellite communication applications. Microstrip antenna has advantage of Low Profile, easy to fabricate, easy to feed, incorporate with other array elements and other microstrip elements. In this paper a rectangular microstrip antenna (RMSA) is designed for 4 GHz resonating frequency. The Substrate height is doubled so that effective dielectric constant is changed. As a result of this, it enhances the bandwidth of RMSA. RMSA is simulated using HFSS , using epoxy substrate of relative permitivity Er=4.4 and thickness of 1.6mm and 3.2. Results describes that bandwidth enhancement can be obtained by increasing the height of substrate.