Wideband RFID Tag Antenna Design

As an automatic identification technique without touching, radio-frequency identification(RFID) technology use radio waves carrying information stored about the identified object or commands to identify objects via space coupling ,such as inductive coupling or electromagnetic wave propagation. Compared with other identification technologies, RFID technology used for identification has many advantages, of which the most potential one is the huge market for RFID system applications. Thanks to the rapid development of electronic techniques and manufacturing technology, the RFID applications based on the wireless and radar techniques emerge rapidly, which will be found very useful in many fields, such as goods stocking and distribution, supply chain, commerce and trade, manufacturing, identification, and security management. As a vital and integral part of RFID system, RFID antennas have received much attention, and their design is very urgent and significant. In fact, the development of RFID antenna is of theoretical significance and practical value for the RFID system.First, a brief introduction to the RFID technology is given, the operating principle of RFID system and related knowledge are described, and meanwhile the antenna in RFID system is analyzed and discussed. The thesis includes following aspects. First, the impedance chart of constant power transmission coefficient for matching between antenna and chip is drawn, according to the impedance matching concepts, a double-T tag antenna is analyzed; Based on which, a new double-UT tag antenna in UHF band is proposed by adding a double-U patch to a double-T antenna in order to obtain wideband performance, and the bandwidth is broadened efficiently around 28%. In addition, the equivalent circuit model is proposed to show the physical connection of the tag antenna; The proposed antenna can be tuned to match with the chip impedance with resistance between 35Ω～87Ωand reactance between 158Ω～247Ωby tuning the double-T matching network, so the new type antenna can be matched to different RFID chips; Finally, some problems facing in RFID system application are analyzed and discussed. Solutions are given, and relative calculations are also implemented.The work was supported by "research on RFID tag antenna design technology" of National High Technology Research plan (863 plan).