Design And Analysis Of Miniaturized Rfid Antennas In UHF-BAND

As a very promising technology, RFID systems have been widely used in the social, economic, defense and many other fields, with the development of the radio frequency identification technology, its components are facing the problems, such as:miniaturization, conformal-based, low loss, low-cost and so on. The miniaturization of the RFID antennas is increasingly becoming one of the research focus. Among all the bands of RFID, the research on LF and HF bands has been relatively mature in China, while the UHF-band which is the fastest-growing and the most widely used is one of the urgent issues that need to be researched by the scholars. The miniaturization of RFID antennas in UHF-band is researched in this paper.In this paper, the Electromagnetic Simulation Software based on the Finite Element Method is used to research the miniaturization of the RFID antennas in UHF-band, including the miniaturized design and analysis of the tag antennas and reader antennas. The thesis of meader-line is the main method, including bending the arms of the dipole tag antennas and opening the meader-line slots on the microstrip antenna, for example, slotting on the patch or floor and so forth. Through the analysis of these antennas, the meander-line method is confirmed an effective way to miniaturize the antennas, while openging proper slots on the floor makes the maximum gain of the patch antennas much higher in a certain extent.The centrosymmetric tag antenna was designed creatively in this paper, which is meandered several times, the omnidirectional radiation pattern was ensured while the antenna was miniaturized, with the size of only 22.5mm x 30.5mm x 1.6mm, which is much smaller than the antennas in the literature that have been published. Moreover, introducing the impedance adjusting arms makes the matching between the antenna and the chip much convenient, using the FR-4 as the material of the substrate ensured the low cost of the antenna, the antenna was fabricated on the single printed circuit board without any hole,the measured results were well consistent with the simulated results.The improved reader antenna used in the hand-held reader has the size of 70mmx70mmx3mm, the circular polarization was ensured while the antenna was miniaturized,opening the slots on the floor was introduced to increase the maximum gain of the antenna,the antenna was compared with the reference antenna in the literature, with the same material of the substrate,the improved antenna has a much higher gain,and the size was reduced by 40%, its bandwidth of the 3dB axial ratio covers one of the UHF-band in China:920MHz-925MHz. In addition, another reader antenna with the size of only 14mmx30mm×1.6mm based on the the chip NRF905, which is used in the watch in wireless temperature measuring system is designed in this paper. An obvious much smaller size is achieved compared with the existing RFID reader antennas in UHF-band, combined with the active tag, it can meet the requirements of the detection distance of the near-distance RFID systems.