Research On UHF Near-field Electric Field RFID Reader Antenna With Uniform Field In Three-dimensional Direction

RFID(Radio frequency identification)is a new technology of target information feedback and detection,which can automatically identify target objects and exchange data in a non-contact way.The traditional far-field RFID system is easy to misread the tags when it is applied in the near scene.Therefore,the RFID read-write technology in near-field is proposed.In practical near-field applications,the read-write area is required to be controllable and can identity tags which are placed in any direction.Therefore,the field uniform of RFID reader antenna in three-dimensional direction which is used in near field is required.Ultra high frequency(UHF)band can identify target objects in long,read multiple objects,and has high speed.This paper is still studying RFID reader antenna in UHF band.Firstly,the three-dimensional electric field uniform can be achieved by multi-feed.The antenna has four branches with matched loads at the end of each branch.When the feeding ports work in different directions at different times,the current distribution over the antenna surface is different,so that the electric field in different directions of the antenna are uniform and controllable.Secondly,the proposed antenna has weak electric field in three-dimension,a new multi-feed antenna with parasitic patch is proposed.The parasitic patch radiates the equivalent current in X and Y direction which can make the horizontal electric field strength in three-dimension stronger and more uniform.Finally,a reconfigurable spiral array antenna is proposed.The antenna is a multi-layer structure.The top layer is planar spiral array,the middle layer is mental ground and the bottom layer is feeding network.The effective working area of the array antenna can be controlled and the uniform distribution of the three-dimensional electric field can be realized by the switches which are simulated by soldering in the feed network.The three antennas have been simulated,processed and tested,and the simulations and test results are good.This project solves the problem of nonuniform distribution of electric field in three-dimensional direction of near-field RFID reader antenna.