Ultra-surface Broadband Circular Polarization RFID Reader Antenna Design

With the rapid development of the Internet of Things(IoT),radio frequency identification(RFID)technology has become a hot topic of research.The technology uses reader antennas and tags to achieve short-range communication.During the entire communication process,the reader antenna actively identifies the tags and interacts with them.Therefore,the quality of the reader antennas directly determines the performance of the RFID system.Among the numerous designs of the reader antenna,the circular polarization method can more perfectly match the polarization of the tag,thus becoming the mainstream design method of the antenna of the application.Firstly,this paper summarizes the technical background of RFID and the design scheme of reader antenna,and discusses the research status of the development of circular polarization and metamaterial at home and abroad.Based on this,combined with metamaterials,a broadband circular-polar UHF RFID reader antenna was designed.The full text work is summarized as follows:An eccentric loop patch antenna with a wide bandwidth(BW)using an L-shaped ground plate to load the air layer was designed to completely cover the global UHF RFID band with an impedance bandwidth of 45.1% and orthogonal to its strip line.A rectangular slot is formed at the position to form a short circuit band to achieve circular polarization(CP)of the antenna.After slotting,the center frequency of the antenna is 860 MHz,with an impedance bandwidth of 25.28% and an axial ratio ratio(ARBW)of 3.5% at the center 857 MHz,and a good right circular polarization Gain of about 7.7dB is achieved at a center frequency of 860 MHz.CP work can partially cover all frequency bands in some frequency bands in China and in other countries such as Europe.An asymmetric cross-fractal metamaterial structure was designed,combined with the derivation of its constitutive parameters,the dielectric constant and magnetic permeability were extracted and verified,and the results satisfied the requirements of metamaterials.Analyze the influence of the material structure parameters of the metamaterials on the material properties and the loading effect.The purpose is to reduce the frequency band of the antenna and enable the CP to cover the RFID UHF application frequency band in China.The metamaterial and the eccentric loop patch antenna are combined to analyze the influence of the relative position of the metamaterial,the structural parameters and the unit distance on the performance of the antenna,and finally the integration of the metamaterial and the antenna is realized.The final simulation results show that the center frequency of the antenna is reduced to 840 MHz,with a 23.9% wide impedance bandwidth,and the impedance matching effect is improved to completely cover the global RFID UHF application frequency range;the axial ratio center is also reduced to 840 MHz,with an ARBW of 2.9%.The right circular polarization gain of the center frequency is 7.73 dB,which realizes full coverage of the RFID reader antenna CP operation in the 840MHz-845 MHz band in China.