High‐gain circularly‐polarized loop tag antenna for long reading distance RFID application

ABSTRACT A simple circularly polarized (CP) square loop antenna for UHF band RFID tag is proposed to overcome the polarization mismatch problem between reader antenna and tag antenna. To achieve good CP radiation, an open gap is introduced onto the square loop. Also, the technique of loading a matching stub across the RFID chip is applied to the proposed loop tag antenna, and good impedance matching between the antenna and RFID chip can be achieved by tuning the matching stub. The proposed loop tag antenna shows desirable antenna gain and good reading distance performance, and its measured reading distance reaches to 17.6 m. Therefore, the proposed antenna is an excellent candidate for various RFID applications in the UHF band, especially those that may require long reading distance. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2335–2341, 2014