Aim: In this work a Rectangular Microstrip Patch Antenna is designed by replacing conventional substrate with Air substrate and by adding a U shaped slot in Patch for Gain Enhancement. Materials and Methods: The Microstrip Patch Antenna with Air Substrate is used with 20 samples in comparison with FR-4 substrate of 2mm thickness. Results: Simulation is done by using Ansoft HFSS (High Frequency Structure Simulator) software. The performance of the Antenna is analyzed in terms of Gain, Directivity, Return loss, VSWR and enhancement in Gain is by 1.724 dB in comparison with FR-4 substrate. Attained Significance accuracy ratio (< 0.05). Conclusion: Microstrip Patch Antenna with Air substrate and U Slotted Patch performs better in terms of Gain.