In this paper, the design, implementation, and experimental validation of a wideband circularly polarized square slot antenna (CPSSA) is presented. The proposed antenna comprises of an irregular square patch, asymmetrical grounded-L strips, an inverted-L grounded slot, a parasitic asymmetrical rectangular split ring resonator (RSRR) and inverted-L strip patches with the overall size of 0.305λL × 0.305λL × 0.007λL. By appropriately embedding strips, slots and parasitic patches on the antenna structure, the measured wideband 3-dB axial ratio bandwidth (ARBW) of 83.2% (2.33–5.65 GHz) is obtained, while the measured impedance bandwidth (IBW) of 86.72% (2.165–5.48 GHz) is achieved. Overall, CP bandwidth is 80.66%. A parametric study of different design parameters is investigated, and the overall performance of the antenna is presented.