Research On Antenna Of RFID Reader

With the rapid development of the Internet of things industry,RFID technology is widely used in identity recognition,automatic charging,wireless positioning and other fields,and has become one of the most popular technologies in the 21 st century.As an important part of RFID system,the performance of reader antenna has great influence on the recognition ability of the whole system.In this thesis,reader antennas for UHF and microwave bands in the far field are studied.Based on microstrip monopole antennas with two types of radiation patches,three kinds of reader antennas are designed.The details are as follows:1.According to the requirements of universality of global UHF band and circular polarization,a omnidirectional and circularly polarized antenna for global UHF band is proposed,which is based on the microstrip monopole antenna with polygonal radiation patch.It contains a V-shaped edge ground and a asymmetrically polygonal radiation patch eccentrically fed by microstrip line to achieve circular polarization and broadband characteristics.The overall size of the antenna is 90 × 100 × 0.8mm3,the impedance bandwidth is 154MHz(0.818-0.972GHz),and the axial ratio bandwidth is 211MHz(0.819-1.03GHz).The maximum gain of the antenna in the main axis direction(+ Z direction)is 2.1d Bi and it radiates a right-handed circularly polarized wave.It has the good characteristics of impedance bandwidth and axial ratio bandwidth,compact structure and omnidirectional radiation,which can be used for handheld reader.2.According to the requirements of universality of global UHF band and circular polarization,a directional and circularly polarized antenna for global UHF band is simulated,which is based on the microstrip monopole antenna with polygonal radiation patch and a metal reflector.By setting a metal reflector,directional radiation and large axial gain are realized.The overall size of the antenna is 180 × 200 × 89.5 mm3,and the frequency range of the reflection coefficient value less than-10 d B line and the axis ratio less than 3d B line both can cover the global UHF band.When the center frequency point is900 MHz,the maximum gain of the antenna in the direction of the main axis is 6.79 d Bi,the half power beamwidth is 83.6°,and it radiates a right-handed circularly polarized wave.The antenna has the good characteristics of impedance bandwidth and axial ratio bandwidth,large axial gain and directional radiation,which can be used in fixed channel gate and other occasions.3.According to the requirements of universality of 2.45 GHz and 5.8GHz in microwave band and circular polarization,an omnidirectional and circularly polarized antenna for 2.45 GHz and 5.8GHz in microwave band is simulated,which is based on the microstrip monopole antenna with multi branch radiation patch.It is eccentrically fed by microstrip line and contains the V-shaped edge ground and radiation patch composed of arectangular branch and a L-shaped branch,which realizes circular polarization and dual frequency characteristics.The overall size of the antenna is 35×40×0.8 mm3,and the impedance characteristics and axial ratio characteristics both meet the requirements.In the two bands,the gain of the antenna in the main axis direction is respectively stable at1.65 d Bi and 0.68 d Bi,and it radiates left-handed circularly polarized wave and right-handed circularly polarized wave respectively.The antenna has the good characteristics of impedance bandwidth and axial ratio bandwidth,compact structure,dual frequency operation and omnidirectional radiation,which can be used for handheld reader.