Rfid Reader Antenna Based On EBG Structure For UHF Band

RFID technology is a long-distance automatic identification technology.Because of its small size, high speed and high sensitivity in identifying, it is widelyapplied in electricity, transportation, health care, environmental protection and otherfields. These years, the RFID technology based on mobile phone platform, in thebackground of mobile communication’s fast development, has caught more andmore attention of the researchers. In the whole RFID system, the key technology isthe design of tag and reader antennas. Since planar inverted-F antenna obtains theadvantages of both monopole antenna and microstrip antenna, it has graduallybecome the most commonly used commercial antenna in mobile terminalapplications. The most important feature of the EBG structure is its electromagneticband gap characteristic, which means it has the ability to suppress the surface wave.If the EBG structure is applied as the floor of an antenna, then the surface wave onthe antenna floor can have a good inhibition to avoid the secondary radiation. In thisway, the backward radiation of the antenna is reduced, thus to improve the gain anddirectivity of the antenna.In this thesis, a planar inverted-F antenna used in RFID reader based on mobilephone platform is designed. And the EBG structure is applied as the antenna floor.The simulation results and experiment results are very satisfactory, both of whichare consistent with the theoretical research and have good agreements.Firstly, the thesis summarized the basic theory and miniaturization methods ofplanar inverted-F antenna. Basing on the theory, a kind of planar inverted-F antennais designed and optimized by the engineering electromagnetic simulationsoftware-CST Microwave Studio. Its innovation point is the radiation patch of theantenna has three slots, therefore the antenna resonated in4frequency bands, whichare0.78~1.04GHz，2.20~2.45GHz，3.38~3.61GHz，16.49~19.59GHz. The lowest band0.78~1.04GHz covers the target frequency0.92~0.925GHz perfectly.Secondly, the principles and analysis methods of the EBG structure werediscussed in the thesis, and the fractal principle was also used in the design of EBGstructure. Two kinds of EBG structure that satisfied the design requirement weredesigned and simulated by CST Microwave Studio. One of them is the Archimedesspiral type, its band gap is0.91~0.93GHz, the other type is the “gong”-shapedfractal, and its band gap is0.78G~1.27GHz, both of which can meet the operatingfrequency requirement.Finally, the planar inverted-F antenna and the EBG structure were combinedtogether to be simulated, then the PIFA (Planar Inverted-F Antenna) with EBG floorwas processed and experimented. It means the EBG structure acted as the floor ofthe antenna replacing the PEC. The simulation results were compared with theexperiment results, it was discovered that their return loss agree well with eachother. In addition, the gain of the two EBG-PIFAs improved by0.56dB and0.69dBthan the classical PIFA. Moreover, the far field pattern of the EBG-PIFA showed astronger ability to inhibit the backward radiation than the common PIFA, with amore prominent main lobe and a better directivity.