Research On The Antenna Of UHF RFID System

Radio Frequency Identification(RFID) which uses radio frequency singals for automatic identification of objects is a rapidly developing technology, especially UHF band RFID technology. With the frequency of RFID system increasing, antenna design has become more and more important. Antenna technology on the UHF band RFID system is studied in this thesis, and the main work and innovation points include:Firstly, theoretical methods of the tag antenna and the reader antenna design are investigated and the emphasis is placed on the tag antenna. The result indicates that radiation gain and power transmission coefficient from tag antenna to chip should be considered in the first place in order to ensure the basic reading and writing distance of the tag. The way to improve power transmission coefficient is to design the tag antenna and make sure its input impedance conjugate matching to the chip input impedance.Secondly, a kind of low-cost miniaturized UHF band RFID tag antenna with the form of transformative dipole is studied and designed in this thesis. Its input impedance can be regulated by adjusting antenna short line. The real and imaginary part of tag antennas designed by the method in this thesis can be regulated from 30 to 50Ωand from 150 to 300Ωrespectively, which can meet the requirement of conjugate matching between the tag antennas and most chips. In addition, miniaturization design of the antenna can be carried out by bending two arms of the dipole. The size of the tag antenna optimized by this method in this thesis is 52mm×44mm×0.5mm and reduced by 40 percents comparing with other tag antennas of the same kind. Because of symmetrical design, the main radiation direction points to the front and back sides of the tag which makes it easy for the tag to be read by the reader. The designed tag antenna is fabricated finally and the measurement method of input impedance is analyzed.Thirdly, a kind of low-cost miniaturized UHF band RFID reader antenna, the size of which can be miniaturized by the patch hole digging and increasing the permittivity, is also studied and designed in this thesis. Furthermore, the influences on the antenna performance by all kinds of antenna parameters are further researched and that performance of the antenna is sensitive to the length of top patch side d, the width of patch dig hole e and the permittivityεis indicated. The size of the optimized antenna is about 110mm×110mm×3mm while the gain is 2dB, which size is reduced by 70 percents and bandwidth of return loss and axial ratio is increased by 75 percents and 60 percents respectively comparing with the same kind reader antenna. Meanwhile, the size can be adjusted according to the demand of gain. The designed reader antennas in two kinds of parameters are fabricated finally. The measured and the simulated results are in good agreement and validity of the design method is proved.