Research On Near-field RFID Antenna Based On Magnetic Coupling In UHF Band

With the application of ultra-high frequency(UHF)near-field radio frequency identification(RFID)technology in logistics management,library management,supermarkets and other scenarios.The nearfield antenna using the magnetic coupling principle has good ability of resist liquid targets and avoid crosstalk.Therefore,it has received extensive attention.However,how to make the designed magnetically coupled near-field antenna have a strong magnetic field and a uniform magnetic field distribution has been a difficult point.Based on the theory,the principle of magnetic coupling of antenna is deduced.Based on this,a magnetically coupled near-field antenna with uniform magnetic field strength and a magnetically coupled near-field antenna with two-layer structure are studied.The main contents and results of this paper are as follows:In the first part,based on the basic theory of electromagnetic field,the magnetic coupling theory model is established for the magnetic coupling principle of near-field antenna,and the theoretical model of magnetic coupling is established by Matlab software.The current is obtained when two parallel metal wires are connected.When the equal amplitude is inverted,the magnetic field generated in the middle is strong and the distribution is uniform.Finally,the theoretical model is analyzed by HFSS electromagnetic simulation software and the correctness of the theory is verified.In the second part,using the magnetic coupling principle of the first part,the dipole antenna is arrayed,and a UHF band RFID near-field antenna with a wide range of magnetic field strength is designed.The antenna adopts a two-stage unequal power feed network to make the designed antenna have a strong magnetic field and a relatively uniform magnetic field distribution in the read area.The antenna uses a Double-Sided Parallel-Strip Line(DSPSL)as the transmission line,which makes the antenna have a large impedance bandwidth.The measured impedance of the antenna is 244MHz(750MHz-994MHz),and the effective read area is 460mm×161mm.When the power of the feed port is 25 dBm,the 100% read distance of the antenna to the tag is 70 mm,and the farthest read distance is 100 mm.In the third part,aiming at the problem of poor environmental stability of the double-sided radiating antenna in the previous part,a double-sided structure is used to design a magnetically coupled microstrip near-field antenna with single-sided radiation,which has good environmental stability.The antenna solves the problem that the original antenna magnetic fields cancel each other by adding a coupling unit connected to the ground.At the same time,the radiation unit of the antenna satisfies the principle of magnetic coupling,so that the magnetic field generated by the antenna is superimposed in the read area.At the same time,the antenna adopts a microstrip line structure with single-sided radiation,so it has better environmental stability.After actual measurement,the impedance band of the antenna is 14MHz(910.5MHz-924.5MHz),and the effective read area is 64mm×56mm.When the power of the feed port is 25 dBm,the 100% read distance of the antenna to the tag is 40 mm,and the farthest read distance is 50 mm.