A new ultra wideband probe-fed microstrip patch antenna has been designed and fabricated. Two perpendicular rectangular slots were incorporated to perturb the surface current, introducing capacitive reactance which counteracts the inductive reactance of the probe that is responsible for the excitation of additional resonant modes. A comprehensive parametric study has been carried out to understand the effects of various dimensional parameters and to optimize the performance of the antenna. A 3.8-8.6 GHz impedance bandwidth has been achieved for VSWR ≤ 2. The radiation pattern is nearly stable as the frequency changes along the bandwidth with maximum radiation in the broadside direction. The final antenna peak gain is changed from 4 dB up to 7.5 dB and the radiation efficiency varies from 62% to 80 % through the operating impedance bandwidth. The proposed antenna has been examined using two simulation techniques, HFSS and FDTD home-made MATLAB program. A prototype of the proposed antenna has been fabricated and experimentally measured. The measurement results are in very good agreement with the simulated ones. Using such an antenna, many applications, including WiMAX, Wi-Fi, UWB applications, as well as wireless sensor mobile applications would be available.