| Radio frequency identification(RFID)technology is an automatic identification technology for identifying the target and acquiring relevant data via non-contact and bidirectional data communications in radio frequency mode.The application of RFID utilizes the electromagnetic wave characteristics of certain penetrability to identify targets.In the UHF band,passive RFID system rise superior to complicated weather conditions,which can automatically identify,track and manage under non-contact conditions all-weather,and also has the advantages of strong environmental adaptability and anti-jamming capability.Thus it has broad application prospects in manufacturing,retail,logistics,transportation and other industries.Data communication in UHF and microwave is based on the theory of electromagnetic wave backscattering.Reader antenna and electronic tag antenna play the role as the interfaces between the reader and electronic tag chip for data communication,as a result,the antennas' performance directly affects the sensitivity and read-write distance of RFID system.Therefore,the research and design about UHF RFID antenna structure is of great significance in both theory and application.In this paper,the theoretical designing way of passive UHF RFID tag antenna based on the characteristic of dipole structure was mainly studied,and the methods of impedance matching and impedance measurement about antenna was stressed on.With an eye to the tag chip on the impedance characteristics of high Q value,two the RFID tag antennas have been designed by dissimilar matching way of coupling loop structure and T type matching network,under the national military standard GJB7373-2011.These designed tag antennas have achieved both high impedance matching with the specific tag chip UR3P2-T and outstanding antenna performance of directivity,gain,impedance and bandwidth.Besides,expertly impedance measurement has been done for practical antennas in enantiomorphic method to acquire the return loss state and impedance matching degree.By comparing the results of simulation and measurement,feasibility of the designing antennas have been validated.Firstly,the implementation principle of tag antenna design and specified some key performance parameters in the design was discussed,emphatically analyzing the mechanism of achieving 900 MHz UHF resonance with half wave dipole and discussing the effect of two kinds of impedance matching network for inductive antenna impedance and their different implementation adjustment methods on the real part,imaginary part impedance,to prepare for the tag antennas design of the main radiation structure and the matching structure.Secondly,the structure meanding technology in half wave dipole was researched for design and size reduction of the main radiating structure of the tag antenna.The coupled ring matching and T matching network structures were ameliorated and embedded into the main radiating structure,based on which two antenna models have been build respectively.The results after simulation and analysis showed that the antennas' performance of omnidirection,gain,impedance and bandwidth is sufficient for the design requirements.Finally,comparison and analysis were carried out on different measurements for antenna impedance and combining the existing experimental condition,the mirror test platform was selected and set up at last to measure the impedance of these two antennas.Through the impedance matching result,the return loss state of the antenna port was acquired.The reasons for the actual test discrepancy is analyzed by comparison between the test and simulation results. |
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