Research And Design Of UHF RFID Reader Antennas

Nowadays,with the update and iteration of wireless communication technology,the Radio Frequency Identification（RFID）technology has developed rapidly,which has gradually replaced the traditional identification method.Among all the application frequency bands of RFID,the Ultra High Frequency（UHF）band has been widely used because of its excellent performance.And as one of the core components of the RFID system,the reader antenna determines the information interaction capability of the entire system,so it is substantial for the exploration of high-performance reader antennas.Towards the problem of various technical standards in UHF frequency bands of RFID specified by different countries,this paper analyzes high-performance RFID reader antennas in the UHF frequency band and is dedicated to the research on circular polarization,broadband,and generalization of the antenna.The main contributions of this thesis are the following.Firstly,three general circularly polarized reader antennas are designed with the coplanar waveguide feeding method.The first antenna adopts an inverse L-shaped radiating patch and introduces the perturbation structure by loading three rectangular grounding branches of different sizes on the right side of the antenna,which changes the surface current of the antenna to realize the circular polarization characteristic and excite multiple resonance points.As a result,bandwidth is extended.The frequency range of the antenna is from 690MHz to2050MHz,and the antenna has circular polarization characteristics in the frequency band from 770MHz to 1260MHz.The physical test results are basically consistent with the simulation results.For the second antenna,the radiating patch is designed to be similar to an inverse T-shaped structure.The perturbation structure is introduced through a notch on the right side of the antenna and a ground stub on the floor,which enables the antenna to achieve circular polarization.The S₁₁parameter of the antenna is less than-10d B in the frequency band of 770-1180MHz,and the axial ratio value of the antenna is less than 3-d B in the frequency band of 810-1310MHz.The third antenna applies a T-shaped radiating patch with an eccentric feeding structure.And the volume of the antenna is reduced by cutting the floor,which is more uncomplicated to generate phase difference of current to meet the requirements of circular polarization,through the asymmetric structure of the floor on both sides of the feeder.The corresponding working frequency band range of the antenna is780-1240MHz,and the axial ratio frequency band range is from 839MHz to 1010MHz,which has stable gain and good directional radiometric characteristics in those frequency bands.All three antennas can be employed in RFID systems based on the global UHF band.Secondly,a universal circularly polarized reader slot antenna with microstrip line feeding is designed.The eccentric setting of the feeding structure strengthens the coupling between the radiating patch and the left side floor,which in turn improves the impedance matching characteristics of the antenna.In addition,the antenna achieves good circular polarization performance by grooving the floor and introducing T-shaped branches.The return loss bandwidth and circular polarization bandwidth of the antenna are410MHz（710-1120MHz）and 220MHz（820-1040MHz）respectively.The maximum gain for the antenna in the frequency band reaches 3.5d Bic.Meanwhile,the antenna size is only100×100×0.8mm³.Also,it can meet the application requirements of the global UHF RFID system.