Research On UHF Electric Field Coupling RFID Near-field Multi-polarized Antenna

Radio frequency identification(RFID)is a non-contact communication technology that uses radio signals to identify specific targets and complete data exchange.The remarkable advantages of RFID such as non-contact,fast reading and writing have attracted widespread attention from experts and scholars at home and abroad.With the rise of the Internet of Things,RFID near-field application scenarios are increasing,and the research on near-field RFID antenna has attracted more and more attention.The design requirements and difficulties of RFID near-field antennas are that the distribution of field strength is controllable.To ensure that the tags in the RFID system are not missed in the area to be read,and are not misread outside the area to be read.The distribution of near-field field strength is relatively complex,and it is difficult to measure with some indicators in the far-field.For electric field coupling reader antennas,To achieve a 100%reading rate of tags placed arbitrarily in the reading area,the electric field distribution in the three-dimensional space of the antenna is required to be uniform and controllable.This paper attempts to introduce an index to measure the uniformity of the electric field components in the three-dimensional direction of the near-field antenna.It proposes an ultra-high frequency electric field coupling RFID near-field multi-polarized antenna.First of all,we propose a novel reader antenna with uniform distribution of electric field components that parallel to the antenna surface.The antenna uses a spiral microstrip line structure with matched loads at the end.The circularly polarized electric field in the plane parallel to the antenna excited by the spiral structure is uniformly distributed,the area is controllable,and no zero point exists.At the same time,the travelling wave antenna a wide impedance bandwidth.It is verified by software simulation that this kind of structure can be used as an antenna element for array design.By adjusting the parameters of the element size,element number,and distance between the array elements,the array can meet the needs of different application scenarios.Next,we propose a reader antenna with uniform distribution of electric field components that perpendicular to the antenna surface.This type of antenna uses a centre-symmetrical microstrip line structure with end-matched load and uses a coaxial feed method at the centre of the antenna.The vertical electric field component excited by the antenna is uniformly distributed,the area is controllable,and no zero point exists.Two different types of reader antennas were simulated and processed.Finally,combined with the above research contents,we propose two schemes to achieve the uniform and controllable of electric field components in three-dimensional.One is a multi-layer structure that combines the spiral structure and the centre-symmetric microstrip structure mentioned above in a reconfigurable manner.The antenna controls the time-sharing work of different radiating patches through switches and realizes the uniform distribution of the electric field components in the horizontal direction and the vertical direction.The other is a single-layer antenna with multi-port feeding,which adjusts the working conditions of different branches by controlling the working state of the feeding port.Both of these methods can achieve the uniform distribution of the electric field components in the three-dimensional direction to meet the multi-polarized design requirements of the UHF RFID near-field reader antenna.In this paper,the electric field components in the three-dimensional direction are discussed and designed.RFID near-field reader antennas with uniform distribution of electric field components in the parallel direction,vertical direction and three-dimensional direction are proposed,which can solve the problems of the near-field application according to different application scenarios.