UHF RFID Tag Antenna Quick Design And Measurement

Radio Frequency Identification (RFID) is an automatic non-contact bidirectional communication identification technology taking advantage of electromagnetic induction and radiation. In recent year, RFID systems are applied in more and more fields, and they have been involved in many aspects of people's daily life. Comparing with 13.56MHz RFID system,860MHz-960MHz UHF RFID system has farther reading distance and faster speed, etc. Nowadays, it has become a hot spot in RFID research. Reading distance is the most important aspect of an RFID system's performance. It is dependent on the gain of tag antenna, the power transmission coefficient which is determined by the matching between tag antenna and microchip, and the power sensitivity. So the tag antenna which determines the system's reading range plays a key role in the overall RFID system.This paper is committed to solve the problems in the research on the design of UHF RFID tag antenna. This paper first introduces working principle, common frequency band, the problems it's now facing of the RFID system and the knowledge of electromagnetic which is needed in the design and measure of UHF RFID tag antenna. Then mainly research on the quick design and measurement of RFID tag antenna and tag antenna design based on metallic surface. The main work of this paper are:(1) In the third chapter of this paper, two structures of RFID tag antenna proposed for RFID tag antenna quick design and optimization. The two proposed antennas present at least 90MHz (840～930MHz) bandwidth for microchip impedance between (10-j80)Ωand (80-j600)Ωunder the condition of reflection coefficient S11 less than-10dB by changing the antenna's two key parameters. Then using the ANN models of the two antennas, we can realize the quick design and optimization of the UHF RFID tag antenna. (2) The existed methods to measure the input impedance of UHF RFID tag antenna was first introduced in first section of the forth chapter, then EM simulation based measurement method are proposed in this paper. It is a de-embedding method based on EM simulation for accurate RFID tag antenna measurement using coaxial line and SMA connector. The measurement result agrees well with the result of the equivalent two ports scattering matrix measurement method and the simulated result. (3)The fifth chapter is focus on the research and analyze of the impact of metallic surface on the input impedance, directional diagram and the gain of the RFID tag antenna. And then summarize the three main antenna structures used on the metallic surface and also give the merit and demerit of these three structures.