High Reliable RFID Reader Antenna Design For Metal Environment

Internet of Things technology is the third wave of the development of the world information industry after computers and the Internet.Radio frequency identification(RFID)is the key technology of the Internet of Things.The reader antenna determines the reading range,distance and stability of the RFID system.The far-field and near-field RFID reader antenna used in complex metal envi-ronments is studied in this paper,and the main research content and innovations are as follows.A multi-polarization beam scanning antenna is proposed based on four in-verted F antenna elements and the RF switch.A 100%reading rate can be achieved for the far and near field tag and anti-metal tag in metal cabinet with a reading zone of 45×90×90 cm3.The angled dipole with grounded metal wall is designed to extend the beamwidth of the antenna.The circular polarization is obtained by two wide beamwidth angled dipole which are placed orthogonal to each other and fed by Wilkinson power divider.The impedance bandwidth of the design covers UHF frequency band in China,America and Europe.The gains at 842 and 915 MHz are 3.78 and 4.78 dBi,respectively.The xoz-and yoz-plane beamwidths are greater than 106 degrees.A two microstrip line loaded(DMLL)loop unit is proposed and the equiv-alent circuit is analyzed.The designed DMLL loop unit has the advantages of uniform magnetic field,simple structure and suitable for configurable array.Based on the RLML loop unit,the 1×8,2×3 and 1×4 loop antenna arrays are de-signed in this paper.The measured bandwidth ranges from 894-964 MHz for 1×8 array antenna with a reading area of 570 mm×150 mm and 917-932 MHz for 2×3 array antenna with a reading area of 270 mm×240 mm.The reading dis-tances of 1×8 array antenna for loop-like tag,dipole-like tag and anti-metal tag are achieved up to 22 mm,42 mm and 45 mm,respectively.For 2×3 array an-tenna,the reading diatances of three tags are achieved up to 23 mm,43 mm and 40 mm,respectively.For 1×4 array antenna,a bandwidth of 13 MHz and a reading area of 400 mm× 170 mm are obtained.