| Internet of Things (IOT), as a new generation of information technology, has aroused the community widespread attention since it was proposed. Countries all over the world regard it as a strategic point of growth for promoting the development of technology and economics. And Radio Frequency Identification (RFID) technology, as an indispensable technology in the perception layer of the IOT, is making rapid progress. RFID technology has experienced more than half a century of development so far from the origin and gets mature day by day, but still needs further improvement and breakthrough. As a part of RFID system, RFID antennas have a direct impact on the performance of the whole system. So the research of RFID antennas is very important for improving the performance of RFID system and promoting the development of RFID technology.In this dissertation, tag antenna and reader antenna with high-performance are designed based on the basic theory of antenna and the key technology of RFID antenna. The specific research contents are summarized as follows:First, key technologies for tag antenna such as impedance matching, miniaturization and bandwidth enhancement are studied. On one hand, a tag antenna which is easy to achieve impedance matching is proposed. By introducing a C-type slot into the original embedded slot patch, a new resonance mode is excited. The length of C-type slot and the distance to the feed can be used to control the resonant frequency and intensity. Combined with the regulation of embedded slot, the real and imaginary part of antenna input impedance can be adjusted independently. Then in order to improve the performance of the antenna, the antenna structure is modified. Four L-type slots are cut instead of the original C-type slot, and the embedded slot at feed source is changed into H-type slot. The modified antenna has not only a wide-8dB|Sn| bandwidth covering the universal UHF RFID band, but also a farer reading range and more compact size compared to the previous design. On the other hand, tag antenna for metal application is designed. Similarly, a simple antenna design is first proposed and then modified. Due to the coupled feeding, wider bandwidth and longer reading range are achieved. In practice, the instability of FR4 permitivity will cause center frequency deviation, and thus degrade the performance of tag antenna. The enhancement of bandwidth can alleviate this problem well.As for reader antenna, theory of circular polarization and typical design methods of circularly polarized (CP) antenna are studied. Firstly, the wide slot is introduced into the design of circularly polarized antenna. By fully utilizing its advantage of wide impedance bandwidth and properly designing the antenna structure, broadband CP operation is realized. For ease of understanding the design principle and transplanting to other bands, detailed design steps are given and key parameters are analyzed. The antenna has a compact size, simple configuration, and a CP bandwidth exceeding 50%. To verify the simulated results, the antenna is fabricated and measured, the measured results agree well with theory. Then, the antenna is transplanted to UHF RFID band according to the summarized design steps. The broadband characteristics is maintained, which shows the superiority of antenna performance and conciseness of design procedure. Finally, compared with some existing RFID reader antenna, the proposed antenna features better over-all properties. |
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