This article presents a new structure of coplanar waveguide (CPW) antenna to enhance the performance by using optimal electrical dimensions. A circularly polarized (CP) broadband open-ground slot antenna has been proposed and analyzed in this work. It resembles a cross-shaped CPW feed structure that is placed in the middle of the square slot antenna. The overall size of the antenna is 0.66λc × 0.66λc × 0.01λc at 4 GHz (where λc represents the wavelength corresponding to center frequency (fc) of the 3-dB CP bandwidth). The antenna is fabricated on the same plane of an FR4 microwave dielectric substrate. Broadband CP operation is achieved by embedding two-square ring slits on the ground plane. Also, to obtain wider impedance bandwidth (IBW) and axial-ratio bandwidth (ARBW), a cross-shaped tuning stub feed line strip and an open slot in the ground plane are used. The peak gain of the proposed antenna is about 5.7 dBi at 3.5 GHz. The results are compared with the reported works; the proposed structure provides a larger ARBW with the same dielectric substrate and comparable size.