Microstrip antenna with S-shaped slot for dual-band circularly polarized operation

A compact circularly polarized microstrip antenna with an S-shaped slot is proposed for dual-band operation. The S-shaped slot is cut onto the centre of a square patch radiator. The measured 10-dB return loss bandwidths for lower and upper bands are 15% and 3.5%, and 3-dB axial-ratio bandwidths are 3.6% and 1.1% with respect to 2.50 GHz and 2.85 GHz, respectively. The overall antenna size is 0.458λo × 0.458λo × 0.095λo at 2.5 GHz.