CP RFID tag design for metal surface mount

A passive UHF band RFID tag antenna design is presented here. To allow circular polarization (CP) radiation, compact size, and metal surface mount characteristics, the radiating square patch is loaded with a cross slot, while an L-shaped open-end microstrip line connected to a tag-chip and terminated by a shorting pin is capacitively coupled to the patch. The 10 dB impedance bandwidth of the tag antenna is measured to be 48 MHz, while its 3 dB CP bandwidth is 6 MHz (922-928 MHz). Further experiment has demonstrated that the proposed tag antenna can provide better reading distance when mounted on a metallic surface as compared with the free-space condition.