Research And Design On Miniaturized UHF RFID Antenna

With the rapid development of the Internet of Things（Io T）,radio frequency identification（RFID）technology has become one of the key technologies of the Io T system with its unique advantages.At present,the RFID system terminal equipment is developing in the direction of miniaturization,which leads to the limitation of antenna size.As one of the most critical components of RFID system,the performance of antenna affects the identification distance,sensitivity and other parameters of the whole system.This paper is mainly devoted to the research of miniaturized UHF RFID reader antenna,the main research contents are as follows:1.A miniaturized end-fire folded monopole reader antenna is designed.The antenna is miniaturized by folding the monopole radiation patch,and the end-fire direction is linearly polarized radiation.The asymmetric ground connection structure is adopted.A long strip protruding on the left side of the ground and a rectangular slot on the right side to adjust the phase of the current.So as to achieve good circularly polarized radiation in the vertical direction.The overall size of the antenna is0.21λ₀×0.29λ₀×0.005λ₀（₀λis the free space wavelength at the center frequency of 915MHz）,and the antenna is suitable for handheld RFID reader.2.A miniaturized ring directional radiation reader antenna is proposed.Firstly,an linearly polarized antenna which is composed of ring patch and ground plane printed upper-layer and lower-layer dielectric substrate,respectively.The radiation patch is a meandered ring structure.Two parasitic patchs are placed in inside of the meandered ring pathch and grounded through vias,respectively.Then,the grounding surface of the on-line polarized antenna is further grooved to reduce the profile height,and a 90°phase difference feed network is set in the ring radiation patch to achieve circular polarization.Finally,the overall antenna size is0.29λ₀×0.29λ₀×0.035λ₀.The measured results show that the relative impedance bandwidth of S₁₁≤-10d B is 13.2%（899-1026MHz）,the relative axial ratio bandwidth is 6.3%（914-976MHz）,and the gain is 6.3d Bi.The antenna has a good directional performance when the ground connection is only slightly larger than the radiation patch,and the structure is simple and the size is small,so it is suitable for application in RFID system in specific environment.3.A low-profile circularly polarized ring antenna with wide beamwidth for RFID readers is proposed.It has two orthogonal tapered coupling feedlines with different sizes which produce circularly polarized radiation.Four grounded arrow-shaped coupling patches which loaded on the four sides of the radiation patch are used to increase the beamwidth and reduce the size.The overall size is0.398λ₀×0.398λ₀×0.024λ₀.The measured results show that the impedance bandwidth of S₁₁≤-10d B is 8.3%（878-954MHz）,the axial ratio bandwidth of 3d B is 4.6%（886-928MHz）,the beam width of 3d B is 190°,and the maximum gain is 4.1d Bi.The antenna has low profile,wide axial beam width and wide coverage,and is suitable for application in top suction environment.