ABSTRACT
The circular polarization of microstrip antenna with single feed or several feeds is usually generated by two stimulated orthorhombic linear polarization waves whose amplitude is uniform and whose phase is 90 degree discrepancy. Single feed circular polarization microstrip antenna has the characteristics of simple structure, lower cost, easily fabrication. Although it only needs to ensure the appropriate feed position so as to engender the circular polarization wave, there is a disappointed AR bandwidth which is about 0.5∼1% of the centre frequency (Wang et al. 2009, Lee et al. 2005). If we adopt the lower dielectric constant and the thicker substrate for the microstrip antenna of single feed and single patch, the relative AR bandwidth will be improved to 6∼14%, but there is a problem that the height of the designed antenna will exceed 50 mm which is the maximum size for UHF RFID readers/ writers antenna (Yang et al. 2008).
