Study Distance Measurement Method Of UHF Passive RFID Tag

Radio Frequency Identification (RFID) technology is a new automatic identificationtechnology, based on a non-contact form for identification of the target object in order toachieve bidirectional transmission of data. In UHF RFID systems, the distance is a veryimportant performance parameters between the reader and tag. When the tag distance ismeasured using the energy spread, affecting many factors of its, mainly includes the gain ofthe tag antenna, the read sensitivity of the tag chip and its impedance matching degree and theeffective isotropic radiated power (EIRP) of the reader and so on.The dissertation conducted in-depth research for the tag distance measurement on thisbasis and designed a new distance measurement method of the tag. The main work includesthe following:First of all, the composition and working principle of the RFID system are systematicallyanalysed, then the composition, classification and working of the tag for a brief introduction.And the way of the two types of data transmission is discussed in detail in the passive RFIDsystem. To ensure a method used in UHF passive RFID system at last, and expounded thewhole working process of the method.The next, this dissertation describes the physical characteristics used in RFID system,and set forth the operating characteristics of the antenna and some important parameters.Focuses on the two measurement methods of read and write distance is studied which used ofenergy, analysis of their merits and the ease of implementation, and then a new method ofutilizing phase difference is proposed to calculate the tag distance. The principle of thismethod is introduced and the process of the specific implementation is analyzed. Thesimulation model was established in MATLAB for theoretical validation of this phasedifference method, then real experiments are used to the verification and determined theexperimental conditions.Finally, this dissertation presented a detailed analysis about the experimental platformand how to select the two signals as I/Q signals. The experiment process is introduced at last.The relationship of the time and phase difference which was produced by the read-writesignal of the passive tags in the process of transmission is of great use to calculate the timerequired by the signal in the transmission, so as to measure the distance. The range error iscalculated for the reader-tag distance below one wavelength and more than one wavelength inthe theoretical simulation and experiments. The experimental results show that the relativerange errors are less than6%for distance below one wavelength. For the reader-tag distancemore than one wavelength, the shorter is the distance, the higher is the measuring accuracy,and the relative range errors are less than10%in the range of918Mhz—924Mhz. The feasibility of thismethod was verified.