Design Of UHF Near-field RFID Reader Antenna

RFID(Radio Frequency Identification) systems have been widely used in industry, commerce and agriculture etc., and the UHF band near-field RFID system is one of the research hotspots. As a result, the design of the near-field antenna of the RFID reader has been gained more and more attention. In the applications of UHF band near-field RFID systems, the non-uniformity of near-field often results in the leakage reading and misreading of RFID tags. Furthermore, the near-field antenna design is complicated and no systematic-theory supporting. The research on field uniformity is important and difficult. To address this problem, three design methods of the near-filed antenna are presented. The main content of this thesis is as follow:(1)Firstly, based on the theory of cutoff waveguide, a novel uniform near-filed antenna design method is proposed, which modifies the antenna floor by using the principle of electromagnetic leakage. The simulations of two designed antennas show that the near electromagnetic intensity of the antenna is uniform and can be controlled by adjusting the size of the aperture on the antenna floor.(2)Secondly, field uniformity is improved by shortening the distance of antenna units and increasing mutual coupling. The long antenna's near field intensity is almost equally distributed, the field intensity with only 2dB difference on a line 300 mm above the antenna. The test bandwidth is68MHz(880-948MHz), covering the America Standard UHF band.(3)Thirdly, the capacitance-loading method is presented to design the uniform near-field antenna.The simulation results show that the field intensity difference above the antenna is only 6dB and the bandwidth is 15MHz(918-933 MHz), which covers the China Standard UHF band.(4)Finally, the RFID testing systems of UHF band are constructed. Experimental results indicate that the systems have good performance and the near-field uniformity around the antenna is also validated. As a result, the effectiveness of the three methods presented in this thesis is verified.