| RFID is an automatic identification technology that makes use of radio wave to communicate. Its basic principle is to carry on the data communication by using the electromagnetic coupling or the inductive coupling between the reader and the tag which adheres on the object, so as to automatically identify the object. As an advanced automatic identification technology, RFID has lots of advantages, such as large storage, readable and writable ability, powerful penetrability, long recognition distance, rapid recognition, long service life, good environmental adaptability, etc.This article focuses on the RFID reader antenna. RFID reader antenna needs to have broadband and circular polarization characteristics. Because microstrip antenna has the advantages of thin section, small size, light weight, high gain, long service life and so on, it is widely used in radio frequency identification system. Therefore the main content of this article is to design a broadband circularly polarized UHF microstrip antenna.Based on the domestic and foreign related literature, this article has designed a new UHF RFID reader antenna. This design has used the rectangular microstrip patch with cornercut and capacitive coupling feed technologies to meet the reader antenna performance requirements in radio frequency identification system. While using a dual-coax feed, compared with the single-feed, the axial ratio of antenna has been effectively improved. This article has also designed a rectangular patch dipole tag antenna used in UHF RFID system. By reducing the slenderness ratio and adding a metal baffle-board, the bandwidth has been widened and the gain has been increased. In addition, because of the dual-feed reader antenna, this article has designed a 3dB Wilkinson power divider as well.Firstly, the article briefly introduces the radio frequency identification technology and RFID antenna. Secondly, the basic theory of microstrip antenna is introduced, including the radiation principle of microstrip antenna; microstrip antenna analysis; single-feed rectangular circularly polarized microstrip antenna theory and the main methods of widening the bandwidth of microstrip antenna, specially, the capacitive coupling feed technology used in this article is described in detail. Thirdly, the designed reader antenna, tag antenna and 3dB Wilkinson power divider are simulated and optimized, and the best design parameters are obtained. Finally, the reader antenna and the power divider are fabricated and measured, and the measure result and simulation result have been compared. To conclusion, there is better consistency between the simulation results and measure results, the designed RFID antennas meet the requirements of RFID system. |
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