| Radio Frequency Identification (RFID) is the product of the rapid development of modern information technology. RFID uses the coupling of energy of the RF to realize wireless and non-contact communication and reach automatic identification. Most importantly, RFID has developed a high technology in Information Technology area in recent years. As technology developing rapidly, more and more mature applications have been involved in all aspects of our daily life.In order to achieve identification between reader and tag, antenna is the essential device in the RFID system. The main faction of the antenna is to transmit and to receive electromagnetic waves through radio frequency Because of a significant role the tag antenna plays in RFID system, a detailed study will be significance.In this thesis, combined with theoretic analysis, modeling and simulation, the work is as follows:1. The books and literature about the theory of antenna and electromagneticfield are read comprehensively and systematically. The theory combined with RFID technology and the theoretical basis needed in analyzing antenna and radiation field have been preliminary studied.2. In this thesis, an in-depth study of tag antenna in RFID system is madebased on antenna theory, mainly about two issues in the tag antenna: the miniaturization of the tag antenna and impedance matching of the tag antenna. Research results at home and abroad have been proposed, and also some classic antenna structures have been proposed.3. This thesis introduces the design and simulation of several studies, as wellas part of processing the results. First the methods for size reduction are proposed and a dipole antenna whose arms are folded along a meandered path is proposed. Then there is an introduction to the planar spiral antenna. By combined with these two characteristics of the antenna, a new resonant frequency tunable double-arm square spiral RFID tag antenna is proposed. It consists of two square spiral arms and two tunable stubs attached to the edge of them. The antenna can work at different UHF band standards from 840MHz to 960MHz by tuning the position of the two stubs with bandwidth unchanged. This encompasses almost the entire bandwidth for worldwide RFID in the UHF band. The dimension of the antenna is around 78mm×50mm and 1.76dBi gain is obtained. The thesis has simulation results of the antenna and has the processed measurement results.4. This thesis also introduces the near and far field tag antenna, and make solution for meeting the need of the far-field antenna and the near-field antenna at the same time. And a Bow-tie dipole tag antenna in the UHF is proposed. The major impact of resistance comes from the inductor loop of antenna. The resistance of the antenna can be tuned from 15-j*100 to 15-j*300 by adjust the inductor loop. The antenna has a bandwidth of 50MHz and 2.2dbi gain is obtained. The thesis described the characteristics of the antenna through the simulation results, and study of the use of antenna structure to achieve impedance matching adjustable is proposed. |
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