Chipless RFID System Based On Variable Polarization Technology

Radio frequency identification (RFID) is a kind of wireless communications technology which exploits radio signal to achieve automatic target recognition. Chipless RFID technology with the advantage of low cost has become the focus of research and development.This article summarized the research achievements of predecessors.The main contributions of this dissertation can be summarized as follows.(I) On the principle of backscatter modulation,the dissertation proposed a chipless RFID system based on the technique of variable polarization which utilized the polarization characteristics of electromagnetic wave, and the indexes of system and components are proposed.The system has advantages of large coding capacity,simple structure and low cost.(II) Two schemes of designing the dual signal source are explained.One is that the DDS output signal provide the phase detect signal for the phase-locked loop,then the phase-locked loop produce the RF signal.And the second is that the DDS output signal mix with the LO signal which produced by phase-locked loop.In additions DDS circuit which can produce a 500MHz signal is designed to solve the image interference problem which is difficult to deal with.After comparing the advantages and disadvantages of the two schemes,the first scheme is chosen to design the dual signal source.(?) The other components are designed including the tag antenna,dUal-polarized antenna,variable attenuator,IF filter and IF amplifier.(?) The chipless RFID system based on the technique of variable polarization is built with the above components.The horizontal polarization branch and the vertical polarization branch are tested respectively using the 2×2 array tag antenna and the 4x4 array tag antenna. Comparing the test result,the 4x4 array antenna is chosen as tag antenna when horizontal polarization branch and the vertical polarization branch are work in the same time.The specific process of the system identify the polarization mode of the tag antenna is proposed,which validates the feasibility of the chipless RFID system.