Broadband Miniaturized Reader Antenna For RFID Application

With the rapid development of the Internet of things industry,radio frequency identification(RFID)technology is widely used in traffic management and control,manufacturing and logistics supply chain,owing to its advantages of fast reading speed,high security and large data storage.Recently,more and more attention has been focusing on realizing the miniaturization and broadband of antennas in the RFID system.This paper focus on the research of the broadband and miniaturization reader antenna,mainly includes the following results.Firstly,due to the different application frequency of ultra-high frequency radio frequency identification(UHF RFID)system in various countries,this paper designs a circularly polarized reader antenna that covers the universal UHF RFID operating band(840MHz~960MHz)based on the characteristics of rectangular slot antenna's multi-mode operation.The joined L-shaped slot in the lower left corner and right grounded T-shaped strip can introduce appropriate perturbation,so the antenna can radiate circularly polarized wave.The total size of the antenna is 100×100×1.6mm~3.Through fabricate and measured,the antenna has an impedance bandwidth of 788~1274MHz with the fractional bandwidth reaches47.1%and an axial ratio bandwidth of 820MHz to 1.124GHz,and the average gain in the axial ratio bandwidth is 1.8d Bic.Impedance bandwidth and axial ratio bandwidth of the antenna both can cover the universal UHF RFID operation frequency band.In the range of error allowing,the test results of the antenna well in line with the simulation results.Then,in order to meet the requirements of miniaturization of the antenna in the UHF RFID system,two miniaturization reader antennas were designed by using the same ferrite material(?_r=7.5,tan?_?=0.01,?_r=7.2,tan?_?=0.2)as the substrate.Antenna still use the rectangular slot structure with broadband characteristics,and the antenna is coplanar waveguide feeding.In order to achieve circularly polarized,a grounded arc-shaped strip embedded in the rectangular slot of antenna.The gain of the antenna in the axial ratio bandwidth is about 2.3dBic,and the circularly polarized beam width reaches104~?.Another antenna uses an annular-ring structure and uses micros-trip line feeding.The antenna can reduce the size and achieve circularly polarized by introducing a pair of bent U-shaped strip-line on the ring patch.Because the micros-trip fed circular patch structure can better utilize the characteristics of ferrite materials,the overall size of the antenna is further reduced,only38×59×1.6mm~3.The circularly polarized beam width of the antenna reaches103~?.The working frequency band of two antennas both cover 920~925 MHZ band of UHF RFID system in China.Finally,an annular-ring slot antenna is designed by still using ferrite material(?_r=6.8,tan?_?=0.005,?_r=6.5,tan?_?=0.15)as the substrate,and its gain and size are between the above two ferrite antennas.The annular-ring slot antenna uses the way of coupling feeding.The antenna achieves the purpose of miniaturization and circularly polarized by embedding the bent U-shaped slot.The gain increased by adding a circular patch and circular slot.The impedance bandwidth of the antenna is 136MHz(875MHz~1.011GHz),and the axial ratio bandwidth is 909~937MHz which covers the 920~925MHz band well,and the gain in the demanded frequency band is around 1.2dBic.