Design And Research Of Miniaturized RFID Tag Antenna

Identification tags are always attached on many products,non-touch RFID technology has been paid more and more attention with the rapid development of logistics.For realizing compact RFID tag,the tag antenna must be low profile and miniaturized size.With decreasing the size,the RFID tag antenna generally presents degraded performances,including low radiation resistance and radiation efficiency,high Q value and narrow bandwidth.Therefore,this thesis designed RFID tag antennas with enhanced bandwidth by analyzing the design theory of RFID tag antenna based on T-match network,presented the detailed design procedure and method.In order to reduce the size of antenna and improve the ratio of product of bandwidth and efficiency to its theory limit,a miniaturized tag antenna with high ratio is designed by adopting circle structure.Additionally,the measurement accuracy of miniaturized tag antenna will be affected by the test fixture,so the measurement method of miniaturized balanced feed tag antenna is also analyzed in this thesis.In chapter 1,according to the relevant literature,this paragraph summarizes the common structures of the tag antenna,performance limit theory and some design ideas of the measurement component.These provide the research knowledge for the future research chapter 2,the basic knowledge about the RFID tag,important design theory and significant formula are introduced.In chapter 3,the equivalent circuit of the planar tag antenna is extracted by using the odd-even mode analysis method.Based on the design goal,the circuit of the ideal Chebyshev band-pass filter is given.By adjusting the structural parameters of the antenna,the components of the equivalent circuit of the antenna are extracted in real time to insure the value of the design antenna is gradually approximated.The final antenna achieves the 2-order Chebyshev filter response.The 3dB bandwidth has a double matching point and the in-band S11 parameter curve is gentle.Through this method,the half-power bandwidth has been broadened effectively.In chapter 4,following the theoretical study of the previous chapter,we study the miniaturized cross-finger tag antenna.We keep the characteristic of 2nd-order filter response.At the same time we try to decrease size of the tag antenna.Since the decreasing radiation resistance which result of decreasing size is difficult to satisfy the request from the theory,we use the smith chart to complete the impedance-match at a single-frequency point.In chapter 5,in order to make full use of the space covered by the limit radius of the external ball mentioned in the theory of performance limit.This chapter designs a planar tag antenna with a circular structure.The efficiency bandwidth product has implemented 12.9% of the limit value.The result succeeds in achieving high performance requirements.In chapter 6,a test fixture is designed to solve the problem of balance conversion during antenna and measure component.For purpose of reducing the interference from the component to the antenna's near-field distribution,this chapter designs a balun component for measuring miniaturized balanced feed antenna.Metal transition layer achieve unbalanced to balanced conversion.The probe with small and length structure can separate the balun component from the antenna's near-field.By this way,we minimize the impact of near-field distribution.Simulation and experimental results show that the component can effectively measure the S parameter of the balance feed antenna.In chapter 7,the main content and work are summarized.The future work is introduced.