| In recent years,with the rapid development of the Internet of Things industry,radio frequency identification technology(RFID)have been applied in many different fields,such as electronic toll collection system,animal tracking and automotive safety and other fields.As an indispensable equipment in RFID system,the antenna becomes a research hotspot for a long time.The main purpose of this paper is to study the antenna used in the RFID reader.The aim is to realize the miniaturization and broadband of the reader antenna.The research contents and achievements are as follows,First of all,since the microwave RFID system has a longer reading distance and higher data transmission rate,and to design a broadband multi-band antenna with circular polarized radiation becomes the difficulty in the antenna design,this paper use microwave RFID application frequency band 2.45/5.8 GHz as the design band,design a coplanar waveguide fed dual-band wideband circularly polarized slot antenna.To achieve circular polarization,an asymmetric slot is introduced in a conventional rectangular slot antenna and a patch with an F-shaped tail is used.In addition,by introducing a T-slot on the ground plane,the axial ratio(AR)bandwidth can be expanded.The antenna exhibits a left-handed circularly polarized radiation characteristic in the boresight direction(i.e.,the +Z direction)within the two AR bands.The measured impedance bandwidths were 2.02?3.10 GHz,and 4.57?6.88 GHz.The two measured AR bandwidths were 2.60?3.20 GHz and 4.85?6.0 GHz,respectively.'Secondly,according to the different authorized UHF RFID band in different countries,we design a circularly polarized reader antenna which can cover the universal UHF band.At the same time,by adding a reasonable perturbation structure to the antenna,the antenna can achieve circular polarization in a broadband range.The overall size is 100×100×1.6 mm3,and the antenna has a working bandwidth of 0.79 GHz to 1.38 GHz with a fractional bandwidth of 54.4%and an AR bandwidth of 0.83 GHz to 1.20 GHz,which covers the universal UHF RFID operation band,and the gain in the operating band can maintain around 3.80 dBi.Finally,in order to achieve the purpose of miniaturization,this paper designed two antennas which work in the 920?925 MHz RFID band in China by using the first-order Minkowski fractal resonant ring as the radiation structure.The first antenna is designed for the purpose of overcoming the difficulty in feeding method of the resonant ring antenna,based on the Babinet principle,the slot structure is used instead of conductor ring,so that the antenna only needs a single substrate.Circular polarization is achieved by feeding a signal of equal amplitude 90° phase difference on the quadrature position of resonant ring.The circularly polarized beam width of the antenna is 107°.The gain can reach 1.70dBic.The overall size is 80×8O×1.6 mm3.Compared with the traditional microstrip antenna working in the same band,the size was effectively reduced.In order to overcome the requirement of a certain width of ground plane caused by the slot loop which make the antenna can not be further miniaturized,another antenna use the resonant ring directly,and used the coupling feeding method to feed the resonant ring.The antenna is a three-layer structure,the air layer between the two layers of substrate is conducive to improve the gain,the circular polarization beam width is 100°,gain in the required band is around 2.10 dBic.The overall size is 60×60×14.6 mm3,resulting in further miniaturization. |
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