Antenna Research And Design Based On RFID System Applications

In recent years, radio frequency identification (RFID) technology has been the focus of wireless communications field. In this thesis, we present some research and designing work for antennas used for RFID applications according to the RFID standards of China. The main research contents include the following three parts: designing of On Board Unit (OBU) and Road Side Unit (RSU) antennas for 5.8GHz Electronic Toll Collection (ETC) system and research on UHF Tag antennas.The first part of this thesis presents the design process of aperture coupled circular polarized microstrip antenna structures used for OBU. A 3dB Wilkinson power divider feeding network is employed to realize right hand circular polarization (RHCP) in the microtrip line feeding structure. Further studies prove that due to the limitations of Wilkinson power divider structure, it is not fit for the new strip line feeding structure. So a new branch line coupler is adopted as the feeding network to realize broad impedance and axial ratio band. The measured results show that a wide 2:1 VSWR bandwidth of 1.4GHz (24%, with center frequency at 5.8GHz) and a gain of 5.2dB is reached. Meanwhile the influences of via holes in the feeding substrate are also presented.The second part introduces a microstrip antenna array research and design for RSU. After a comparison among several different approaches for circular polarized antenna array, a single feed truncated corners microtrip antenna is employed as the array unit. In order to achieve a precise identification of long-distance, at the same time, to avoid adjacent channel interference resulting in repeated-charge of fees, the antenna should has high gain and narrow beam-width characteristics in the horizontal and vertical planes. By carefully adjusting the spacing element and feed lines, the designed 2×4 array is equipped characteristics of simple architecture and easy for manufactured. Based on the measured results, the differences between simulated and measured results caused by substrate influencing factors are analyzed. Finally, the optimization program is presented.The third part of this thesis quotes the theory of impedance matching between tag antenna and IC chip and the tag antenna types. A planar half-wavelength dipole with T-math configuration is presented. A research on antenna's impedance, gain and radiation efficiency variations is done while antenna's conductive medium is copper and conductive ink, respectively. And while the depth of conductive medium varies, the performances of antenna are also analyzed.