Analysis And Design Of Tag Antennas Based On RFID Systems

Radio frequency identification (RFID) is a sort of automatic identification technology developing along with the development of large scale integrated circuit. This technology can identify the target and exchange useful digital information between reader and tags via non-contact radio frequency communication technology. RFID now has been rapidly spreading in industry, commerce, and traffic transport management fields for its advantages such as no direct touch, long working distance, suitable for harsh environment, efficient recognizing capacity etc. As the most important advantage of RFID system is non-contact identification, the key component is the antenna, which is performed as emit or receive device to realize data communication between the tags and the reader. So the development of RFID antenna is of the theoretical significance and practical value for the RFID system.Above all, a brief introduction to the RFID technology is given, including working principles of RFID system and related knowledges. Then, the antenna analytical approach is described simply, meanwhile a broad tag antenna classification and the problems appeared in the antenna design, such as impedance matching are researched and discussed. The main task in this thesis is to study the tag antennas for passive RFID cards working in microwave frequency area. The dipole and the aperture antenna have been analyzed and discussed especially, and the related antennas are designed and simulated subsequently.A dipole for RFID application is presented and analyzed after doing a lot of research on various dipoles, of which smith impedance chart, return loss and directional pattern are discussed respectively. To meet the need of impedance match, a folded dipole whose impedance could be adjusted freely is also introduced. Besides, aperture antenna is an important part in this thesis. A Bio-Tie slot antenna with CPW-fed structure is presented. The designed antenna can operate at the 5. 8GHz band with 21.7% broad band(s₁₁<-10dB) and 5.1dBi gain, respectively. The radiation patterns are almost omni-directional in H-plane. To decrease the antenna dimension, an improved antenna is also presented. After minimization, the antenna shows a dimension of around 48.18 % reduction in area compared with the original one. Besides, the bandwidth is also increased. All these properties and the uniplanar structure make both the antennas suitable for RFID application.