In this work, a new wideband circularly polarized square slot antenna (CPSSA) with a coplanar waveguide (CPW) feed is proposed. The suggested antenna is wrought of one arc-shaped, two inverted-L grounded strips around, two opposite corners of the square slot and C shaped(smile) gap on the patch. In this outline the impedance bandwidth and the axial ratio bandwidth (ARBW) are increased compared to the previous CPSSA designs. In this way, the 3 dB axial ratio bandwidth of the designed antenna improved and reached to more than 57 % (3.2 GHz - 5.7 GHz) and the VSWR (Voltage Standing Wave Ratio) < 2 impedance bandwidth increased as large as 108 % (3 GHz - 10.1 GHz). Overall this work, the optimized method of the axial ratio (AR) and S11are provided and discussed in text. The fabricated antenna results agree well with the simulation analysis.