Research And Design Of RFID Reader Antenna

With the development of communication technology,the field of ultra-high frequency(UHF)radio frequency identification(RFID)has been studied,and RFID technology has been widely used.Antenna as an important part of communication system,its characteristics and performance will directly affect the performance of the system.Near-/far-field reader antennas can be used in RFID systems such as complex goods management,luxury management,access control system,contactless payment,etc.Due to the limitation of installation space and application scope,the miniaturize d and multi-band reader antenna has higher research value,the demand of short-range tag recognition in metal and liquid environment promotes the development and innovation of near-field antenna.On the basis of a lot of research,this paper has done the following work:1.A UHF RFID near-field reader antenna is designed with monopole and segmented line.The antenna can realize the recognition of small area and short distance.In order to further improve the performance and improve the antenna,a UHF RFID near-field reader antenna is designed by using the structure of segmented line loop and zero-phase-shift-line loop.The segmented line is distributed on the upper and lower sides of the dielectric substrate.After optimization,the electric length o f the segmented line is about?/2,which makes the current in the loop in phase,and realizes the high and uniform magnetic field intensity in the near-field identification area above the antenna.2.Based on the first point of near-field theory,a switchable near-/far-field reader antenna for UHF RFID applications is designed based on the structure of two-layer substrate.The lower substrate consists of a phase shifter,a power divider and a PIN diode,and is fed to the folded vibrator on the upper substrate through a copper pillar.The phase of the feed current is controlled by the states of the PIN diode on the lower substrate,and the switching between the near field and the far field is realized According to the investigation,there are few literatures about the same function antenna.The proposed antenna adds an implementation scheme of near-/far-field switchable antenna design,which overcomes the short comings of the traditional near-/far-field antenna that may misread the tag.The near-field operating band of the antenna is 902-928 MHz.When the input power is 30 d Bm,the reading rate of the antenna is 100%in the plane which is equal to the antenna area and within 200 mm from the upper surface of the antenna.In the far-field working state,its operating band can be extended to universal UHF RFID frequency band(840-960 MHz),the peak gain is 6.94 d Bic,and the S₁₁ of the antenna in the band is less than-15 d B.3.Based on the second point of far-field theory,a dual-band circularly polarized RFID reader antenna is proposed.The upper and lower dielectric substrates are used,and the feeding network of the lower substrate is fed to the folded vibrator of the upper substrate through the copper column,and the rectangular patch with notch is directly fed by the coaxial line.The feasibility of antenna design is verified by pro ofing test and result analysis.The antenna can work in universal UHF band and ISM band(2.4-2.5 GHz).The antenna's-10 d B impedance bandwidth and 3 d B axial ratio bandwidth in the low band(high band)are respectively 91.1%(4.9%)and 87.8%(1.3%),the peak gain is 5.48 d Bic(3.63 d Bic)within the operating band,and the radiation pattern of the antenna is symmetric and stable.