RFID读写器

DESIGN OF A COMPACT UHF RFID TAG ANTENNA USING AN INDUCTIVELY COUPLED PARASITIC ELEMENT

Taeik Kim,Uisheon Kim,and Jaehoon Choi

Department of Electronics and Computer Engineering17, Haengdang-Dong,Seongdong-Gu,Seoul,139-791,Republic of Korea;Corresponding author:choijh@hanyang.ac.kr

Received24April2010

ABSTRACT:In this article,a compact tag antenna for UHF RFID systems is proposed.The proposed antenna consists of a T-matching network,meandered dipole,and an inverted-U shaped parasitic element.The tag antenna is miniaturized by utilizing inductive coupling between the meandered dipole and the parasitic element.The overall dimension of the proposed tag antenna is17.96Â35.6mm2.It has a gain of1.52dBi and a maximum reading distance of6.3m at915 MHz.The size of the tag antenna is about33%of that of other RFID

tag antennas,such as a meander line antenna and a coplanar inverted-F antenna.In spite of its small size,the proposed tag antenna yields superior performance.V C2010Wiley Periodicals,Inc.Microwave Opt Technol Lett53:239–242,2011;View this article online at .DOI10.1002/mop.25753

Key words:RFID;tag antenna;inductive coupling;parasitic element

1.INTRODUCTION

Radio-frequency identification(RFID)systems have been inves-tigated extensively as a key technology for future communica-tions.Recently,research has been conducted on various applica-tions of RFID systems,such as electronic toll collection,asset identification,retail item management,animal tracking,and ve-hicle pared with a barcode system,an RFID sys-tem has advantages of identification capability,semipermanent durability,rapid identification,long reading range,andflexibil-ity.For these reasons,logistics companies and distribution mar-kets have replaced traditional barcode systems by RFID systems to improve efficiency and convenience.As most UHF RFID tags have to be attached to small objects,the antenna geometry must be miniaturized without serious degradation of the radia-tion efficiency.Many studies have focused on reducing the size of tag antennas using various configurations,such as‘‘Meander-ing’’and‘‘Inverted-F’’[1].However,compact antennas using meandering lines have low gain and narrow bandwidth.Even though antennas using an inverted-F structure have high gain, the height or size of the antenna becomes large because of the additional ground plane.

In this article,we proposed a compact UHF RFID tag antenna using a parasitic element.To reduce the size of a tag antenna,inductive coupling between a meandered dipole and a parasitic element is utilized.Critical parametric analysis has been conducted,and the performance of the proposed tag antenna is compared with that of existing small tag antennas, such as a meander-line antenna(MLA)and a coplanar inverted-

F antenna(IFA).

2.ANTENNA DESIGN

Figure1shows the configuration of the proposed tag antenna. The proposed antenna consists of a T-matching network,mean-dered dipole,and an inverted-U shaped parasitic element.The tag antenna was fabricated on FR4(e r¼4.4,tan d¼0.02, thickness¼0.6mm).The tag chip used in this study is an Alien

Higgs-2microchip with an impedance of16-j131X at 915MHz.The proposed tag antenna was designed and analyzed using the Ansoft high-frequency structure simulator(HFSS Ver.10)[2].

The T-matching network is often used for impedance match-ing of RFID tag antennas.The impedance of an antenna can be easily controlled by varying the length and width of the

short Figure1The configuration of the proposed tag

antenna

Figure2Input impedance characteristic of the proposed tag antenna versus frequency for various values of G1