A novel shorted CPW-fed slot antenna with wideband circular polarization characteristic is proposed in this letter. The proposed antenna consists of a bi-directional radiation slot antenna printed on a single substrate and a reflector for unidirectional radiation. A half circle slot and a slim slot are involved to optimize the axial ratio (AR) bandwidth and taper on the feeding line is utilised to further improve the impedance bandwidth. The measured results show that the antenna has the impedance bandwidth (S11 <; -10dB) of 12.6% and the AR bandwidth (AR <; 3dB) of 12.7%. The RHCP gain in the main radiation direction is 7.5 dBi.