Design Of Circularly Polarized Antenna For Radio Frequency Identification

One of the development priorities of modern society is to build the Internet of Things.In order to achieve interconnection and interoperability,the Internet of Things in the new era puts forward higher requirements for antenna performance.Based on the application of Radio Frequency Identification(RFID)as the current background,the author has designed three RFID circularly polarized antennas with different structures and performances.The antenna structure and performance are as follows:First,in this paper,a miniaturized planar four-arm helical circularly polarized antenna is proposed.The antenna structure is mainly composed of two parts: feeding layer and radiation layer.The feeder layer adopts a power divider cascade T-section to form a power division feed network with one input and four outputs.The radiating layer is a planar four-arm spiral structure,which is composed of two sets of broken-line radiating arms with different lengths.The two sets of radiating arms are printed on the upper and lower surfaces of the dielectric plate respectively,and are connected by metal vias.The impedance bandwidth of the antenna is 0.81-0.94 GHz,and the relative bandwidth is 14.8%.The antenna has good circular polarization performance within the operating frequency.The beam width is 123°.The peak antenna gain is at the frequency of 0.92 GHz.The peak gain is 4.56 d Bi.The antenna was simulated and processed,and the test results were basically the same as the simulation.In addition,in the experiment of the smart handheld terminal,the antenna's indoor reading distance for single tag and multi-tag reached 11.4m and 13.8m,respectively,at a standard reading power of 1w.Secondly,an asymmetric slot-coupled dual-frequency circularly polarized antenna is proposed in this paper.The antenna structure is a stacked three-layer structure,the lowermost layer is the feeder layer,and the lower surface is a broadband feed network.The upper surface of the feed layer is a metal floor with an asymmetrical H-shaped slot,and the antenna is fed through the slot coupling.The two layers on the antenna are radiating patches of different frequency bands,the middle patch is a circular ring patch,and there is a smaller parasitic split ring inside the ring.The parasitic loop has a current compensation function to improve the antenna gain.The upper patch is a ring-like patch.The antenna was processed and verified,and finally the impedance bandwidth of the antenna was 0.89-1.02 GHz and the simulated high frequency band(2.15-2.55GHz),the 3d B axial ratio bandwidth was 0.89-1.1GHz and 2.15-2.52 GHz,and the peak gain was 4.2d Bi at 910 MHz and 6.33 d Bi at 2.4GHz.The antenna has good directional radiation characteristics,which has achieved the design goal.Finally,a low-profile cross-dipole antenna loaded with AMC structure is proposed in this paper.The antenna evolved from a rectangular patch.Two sets of patches are printed on the upper and lower surfaces respectively,and circular polarization is realized according to the characteristics of the in-phase and out-of-phase currents of the coaxial wires.When loading ordinary metal floors,the antenna impedance bandwidth is 0.87-1.02 GHz,and the axial ratio bandwidth is 0.62-1.5GHz.When loading the new mushroom-shaped AMC structure as a reflective surface,the impedance bandwidth of the antenna does not change much,it is 0.85-1GHz,the antenna gain is slightly improved,and the peak gain is 4.6d Bi at the frequency of 860 MHz,the antenna front-to-back ratio is optimized,and the profile is reduced by 34%,from 85.8mm to 56.8mm.The antennas proposed in this article are all circularly polarized antennas used in RFID.Based on the application of RFID,the three antennas have the characteristics of miniaturization,dual frequency and low profile.In the article,the principle of circular polarization and antenna design are also discussed in detail,and the feasibility of the three antennas is verified in principle.