An UHF RFID Reader Antenna with High Front-to-Back Ratio

In this paper, a circularly-polarized (CP) ultra high frequency (UHF) radio frequency identification (RFID) reader antenna with high front-to-back ratio (FTBR) is designed. The proposed ’#’-shaped electromagnetic band gap (EBG) structure has low profile and broadband band gap function. Thus, high FTBR property could be obtained through suppressing the propagation of surface waves. In order to further improve FTBR, rectangular defected ground structure (DGS) is employed on the grounding plate. The designed antenna operates at 915MHz with gain of 6dBic, half power beam width of 112°, and FTBR of $29 \mathrm{~dB}$ Compared with the antenna without EBG and DGS, the FTBR of this antenna has increased by $14.2 \mathrm{~dB}$. The antenna size is $0.244 \lambda_{0} \times 0.244 \lambda_{0} \times 0.012 \lambda_{0}\left(\lambda_{0}\right.$: wavelength in free space at $\left.915 \mathrm{MHz}\right)$.