Research And Design Of UHF RFID Tag Antenna Based On The EBG Structure For Metallic Objects

In recent years,UHF(Ultra High Frequency)RFID(Radio Frequency Identification)technology has attracted much attention in the field of supply chain management and internet of things due to its long reading distance and low cost.With the diversification of application scenarios,RFID tags need to be attached on the surface of metallic objects.Due to the influence of metal platform,the traditional dipole tags have the problems of impedance mismatch and gain deterioration,which lead to the low reading efficiency.The reading distance is one of the key parameters in RFID system,which is determined by the gain and impedance matching of the tag antenna.At pre-sent,most users tend to buy small size and easy to carry RFID products,RFID products miniaturization requirements are getting higher and higher.Therefore,for RFID tags used in complex metal environments,stable im-pedance matching and good gain performance are achieved by using the structure of EBG(Electromagnetic Band Gap)loaded by dipole antenna.The research contents and main innovations are as follows:Firstly,compact circular-polarized tag antenna for metallic objects is pro-posed.It is the first time that double-layer rectangular ring EBG structure is loaded with a cross dipole antenna to achieve circular polarization radiation in the design of tag antenna.By reducing the polarization loss between the tag antenna and the reader antenna,a relatively long distance reading is re-alized.When the tag is pasted on the metal plane of 200 mm×200 mm and 400 mm×400 mm respectively,the simulation bandwidth of 3 dB axis ratio is 917-923 MHz and 915-921 MHz,respectively.The simulated S11 imped-ance bandwidth completely covers the UHF frequency band,achieving sta-ble impedance matchsing and radiation performance.Theoretically,when the effective output power of the RFID system is 36 dBm,the tag can achieve the maximum reading distance of 5.08 m.Then,a small linear-polarized anti-metal tag antenna is presented.The miniaturization design of EBG cell is realized by means of migration through hole and stack structure.The size of the EBG structure loaded by the ring dipole antenna is 70.5 mm×19.2 mm×4.8 mm.When the tag is mounted on the metal plane of 200 mm×200 mm,300 mm×300 mm and 400 mm×400 mm,respectively,the simulated impedance bandwidth of S11 co-vers 869-962 MHz,and the impedance performance remains stable.By load-ing the EBG structure,the tag antenna achieves stable radiation performance.In theory,the tag achieves a reading distance of 7.7 m.Finally,a long-reading-distance anti-metal tag antenna based on DLS-EBG(Double-Layer Symmetric Electromagnetic Band Gap)is proposed.The DLS-EBG cell uses symmetrical migration through hole and loading middle layer structure to achieve miniaturization,and an equivalent LC cir-cuit of DLS-EBG cell is proposed to verify its reflection performance.The DLS-EBG structure loaded with the meandering dipole antenna achieves stable impedance matching and radiation performance,and the gain is im-proved by 0.88 dBi.When the tag is attached on a 200 mm×200 mm metal plane,the measured impedance bandwidth is 116 MHz(876-992 MHz),cov-ering the UHF band.When the effective output power of the RFID system is 36 dBm,the tag achieves the maximum reading distance of 12.3m on the metal plane of 200 mm×200 mm.