Design And Research Of Passive RFID Tag Antennas

With the advent of the information age,internet of things becomes an inevitable trend in the future.Radio Frequency Identification(RFID),as one of the effective means to identify the target object,has received extensive attention in recent years and develops rapidly.RFID tags can be divided into active,semi-active and passive types according to the energy supply.Passive RFID tag has attracted great attention due to its low cost and high reliability.In this paper,passive RFID tags with and without chip are studied.For the RFID tag with chip,we design a simple,low-cost ultrahigh frequency(UHF)RFID tag with high tolerance on the background materials.The tag antenna adopts the loop structure,,utilizing the meander design to reduce the size of the antenna.Firstly,the characteristic modes(CM)of a rectangular loop is simulated in FEKO.The radiation mode in free space and on perfect electric conductor(PEC)are analyzed respectively,providing guidance on antenna design.Afterwards,the equivalent circuit of the antenna is extracted and analyzed for antenna optimization.Finally,the tag is fabricated and measured in outdoor scenario and indoor scenarios with low and high reflections.The proposed tag antenna achieves the maximum reading distance of 6.1 m and 14.1 m,respectively,when mounted on metal and dielectrics.The measured results are in good agreement with the simulation ones.For chipless RFID tag,three chipless tags,including two linearly polarized tags with non-symmetric and symmetric filters and a circularly polarized(CP)tag,based on retro-reflective structures are designed,in order to increase the reading distance and robustness to the direction of the interrogating signals..Firstly,the design guidelines on how to arrange the filters for higher detection accuracy are provided based on standing wave analysis.Based on the results,retro-radiating tags with 10 filters are designed.Since the E fields from the retro-radiators add constructively in the direction of the incoming signal automatically,the reading distance is greatly increased compared with the conventional tags with orthogonally placed antennas.In order to make the antenna insensitive to polarization and direction of arrival,CP tag and fully symmetrical LP tag are designed.The experimental results measured in anechoic chamber show that the retro-radiator based tag can reach a reading distance of 60 cm,which is longer than most of the existing chipless tags.In the measurement,tag information can be effectively identified even when the reader antennas are not at the boresight.Compared with the current research,the novel RFID tags proposed in this paper have certain advantages in terms of reading distance and environmental adaptability.