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A passive UHF band radio frequency identification tag antenna design is presented in this article. To allow compact size and circular polarization (CP) radiation, a radiating square patch is loaded with two pairs of unequal slits, while a quarter-wave microstrip line connected to a tag chip and terminated by a short-circuited stub line is used to excite the radiating patch. The 10-dB impedance bandwidth of the tag antenna is measured to be 31 MHz (896-927 MHz), whereas its 3-dB CP bandwidth is 6 MHz (911-917 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. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1481-1485, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27607 [ABSTRACT FROM AUTHOR]

A compact circularly polarized circular microstrip tag antenna designed for RFID UHF band is presented.The proposed tag antenna is excited by using microstrip-line coupling-feed method. By choosing the proper lengths of two short-circuited arc microstrip lines and its coupling distance, good complex impedance matching can be obtained. Moreover, a cross slot of unequal arm lengths embedded in a circular patch is used to achieve compact circularly polarized operation. The measured 10-dB return-loss bandwidth of the tag antenna is 40 MHz (901-941 MHz), while the 3-dB axial-ratio bandwidth is 6 MHz (912-918 MHz). Further experiment shows that the tag antenna can provide a significantly increased reading range when mounted on a metallic surface. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1107-1112, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27480 [ABSTRACT FROM AUTHOR]