Antenna Design For Worldwide RFID Applications

Radio Frequency Identification (RFID) is a technology that can be used to identify anyobject carrying an electronic tag by electromagnetic waves. The design of antennas for RFIDapplications has been playing a crucial role in the continuous development of RFIDtechnology. This dissertation was in part by the National Natural Science Foundation of China(60802004), in part by the State Key Laboratory of Millimeter Waves (K201405), and in partby the Fundamental Research Funds for the Central Universities (2014ZZ0031). The maincontents of the thesis include three parts as follow:Firstly, the state-of-the-art of the RFID technology, and the basic performance parametersof antenna are introduced.Secondly, a circularly-polarized Radio Frequency Identification (RFID) reader antenna forworldwide Ultra-High Frequency (UHF) applications is presented. The antenna is composedof two coin-shaped patches, a ring-shaped strip, and a suspended feeding strip withopen-circuited termination. The measurements show that the antenna has an impedancebandwidth (S11<-23dB) of21.9%(771-961MHz) with a small raise around935MHz,3-dB axial ratio (AR) bandwidth of15.9%(816-957MHz), and average gain level of9.1dBic.Then, a broadband single-fed circularly polarized patch antenna is proposed. The single-fedantenna has a simple structure, and consists of a main path, a parasitic path and a groundplane. The simulations show that the antenna has an impedance bandwidth (S11<-10dB) of(825-968MHz),3-dB axial ratio (AR) bandwidth of (860-961MHz), and a gain level of morethan7.1dBic.Thirdly, based on the original proposed reader antenna for worldwide UHF RFIDapplications, a broadband dual-frequency combined reader antenna is proposed, spanningboth conventional universal UHF band of840-960MHz and ISM band of2.45GHz. Thecombined reader antenna is constituted by combining a compact antenna with the originalproposed reader antenna, and the compact antenna internally installed in the squared holes ofthe original proposed antenna. In the UHF band, the simulations show that the combined reader antenna has an impedance bandwidth (S11<-25dB) of811-970MHz,3-dB ARbandwidth of843-964MHz,2-dB AR bandwidth of852-961MHz, average gain level of9.0dBic with a peak gain of9.7dBic, and a front-to-back ratio of more than15dB. In the ISMband of2.45GHz, the simulations show that the combined reader antenna has an impedancebandwidth (S11<-15dB) of2.373-2.704GHz, a gain level of more than8.9dBi with a peakgain of10.4dBi, a cross polarization ratio of20.5dB, and a front-to-back ratio of more than30dB. In addition, the isolation between two radio signal input ports is below-20dB and-26dB in the UHF band and microwave band of2.45GHz, respectively.Therefore, all the proposed antennas in this thesis have the potential use in highperformance global-operability readers for long-rang identification, multi-frequency band andwide-coverage applications.