Novel Miniature Monopole Tag Antenna for UHF RFID Applications

A novel miniature monopole tag antenna for passive UHF radio frequency identification (RFID) operation is presented. The antenna possesses a two-sided structure that is printed on an FR4 substrate and fed by a 50-?? microstrip line. By properly using helical strips and vias, the antenna size can be reduced to a small volume of 10 (L) ?? 9.5 (W) ?? 0.8 (H) mm³ to be easily integrated within various portable devices. A miniaturized quasi-lumped circuit is also designed to achieve a good impedance matching between the antenna and the tag chip. Experimental results demonstrate that the antenna has a suitable operating band about 914-939 MHz and also nearly omnidirectional radiation patterns with proper gain. Moreover, the proposed compact tag antenna, capable of achieving a maximum readable range about 5.6 m with an effective isotropic radiated power (EIRP) equal to 4 W, is well suitable for RFID applications.