Scalable Three-dimensional Uniform Near-field RFID Reader Antenna Design

RFID is a technology that automatically collects item information through electromagnetic waves,and its non-contact,fast,and efficient identification characteristics have been widely used in the information age.In many application scenarios,such as smart bookshelves and drug management,RFID reader antennas must read item tag information at close range.The traditional far-field RFID system is no longer applicable.To solve this problem,scholars propose a near-field RFID system.The reader antenna has a uniform field distribution in the near-field region,and the field strength is rapidly attenuated outside the region.For electrically coupled reader antennas,it is a big challenge to achieve uniform distribution of three-dimensional components of the electric field in the near field area,so that labels placed in any direction will not be missed.At the same time,achieving different electric field uniform distribution ranges is a big challenge in adjusting the antenna unit structure to meet the needs of non-application scenarios.From this perspective,this project designs a near-field reader antenna with uniform three-dimensional components of the electric field and expandable characteristics.Firstly,a multi-layer structure reconfigurable reader antenna is proposed.The antenna can realize the uniform distribution of threedimensional electric field components in the controllable area through the time-sharing operation of the two-layer microstrip structure.The simulation of the electric field component of the microstrip structure with different number of radiation units verifies the scalability of the antenna.The simulation results show that the maximum gain of the antenna in the far field is-5.6dBi.The measurement results show that its reflection coefficient is less than-10dB in the bandwidth of 0.85-0.96GHz,and the reading volume of the tag with a 100%reading rate is 240mm × 200mm ×150mm.Secondly,a multi-layer reconfigurable reader antenna with improved electric field uniformity perpendicular to the antenna surface is proposed.The antenna improves the electric field uniformity of the previous antenna perpendicular to the antenna surface through four bent Microstrip lines that are symmetrically distributed in the center.It can also achieve reading range requirements in different scenarios by adjusting the number of microstrip structure radiation units.The simulation results show that the maximum far-field gain of the antenna is-8.6dBi,and the maximum fluctuation amplitude of the electric field strength perpendicular to the antenna surface is about 1/6 times that of the improved antenna.The test results show that the reflection coefficient of the antenna is less than-10dB within the bandwidth of 0.83 to 0.93GHz,and the reading volume of the tag with a 100%reading rate is 360mm × 400mm × 200mm,the reading range parallel to the antenna surface is three times that of the improved antenna,and the reading height is 50mm higher than the improved antenna.Finally,a reconfigurable reader antenna based on PIN diodes is proposed.The antenna is loaded with 8 PIN diodes on a microstrip structure,and the working state of the diodes is controlled through a DC bias circuit to achieve uniform distribution of the three-dimensional components of the electric field.The simulation results show that the maximum gain of the antenna in the far field is-5dBi.The test results show that its reflection coefficient is less than-10dB within the bandwidth of 0.92-0.93GHz,and the reading volume of the tag with a 100%reading rate is 840mm × 840mm × 250mm,the reading range parallel to the antenna surface is 4.9 times that of the previously proposed antenna,and the reading height is 50mm higher than the previously proposed antenna.