In this paper, a dual wideband microstrip antenna (MSA) has been presented for wireless local area networks (WLAN), worldwide interoperability for microwave access (Wi MaX) and U-NII band applications. The antenna is designed and simulated using CSTMWS V'10. The main goal of this paper is to get multi-frequency behavior by cutting resonant slots into the patch of the antenna and a wideband antenna behavior using an aperture coupled feeding method. The designed antenna has a semi-spiral G-shaped compact structure and an electromagnetically coupled feeding mechanism (aperture-coupled feeding). It is fabricated on an FR4 substrate with a dielectric constant of 4.4 and a dielectric loss tangent of 0.009. The testing of prototype antenna (to measure S11) is done using a vector network analyzer. The measured results are 80% matching to the simulated ones. The parametric study, simulation results, measured results, and applications of the MSA for WLAN, WiMAX, and the FCC unlicensed 5.2 GHz National Information Infrastructure (U-NII) bands are presented in the paper. The antenna shows a simulated gain of about 4.5 dB at the three wireless application bands.