Abstract: A rectangular microstrip patch antenna was designed on three layer substrate for ultra wide band (UWB) wireless communications system. The proposed UWB antenna simply consists of a rectangular patch with microstrip line feeding and on three layer substrate. Where used substrate permittivity is 2.2, 2.33 and 4.4, that is placed on the ground plane. The proposed rectangular microstrip patch antenna was simulated which covers the range of 6.9 to 8.7 GHz. Here study the graph of return loss, input impedance, 2D radiation pattern and 3D radiation pattern.