| Radio frequency identification (RFID) is a non-contact automatic identification technology, the wireless radio-frequency communication is used to proceed non-contact two-way communication, so as to achieve automatic target recognition and access to relevant datas, compared with other identification methods, the technique has high accuracy, speed, environment adaptiveness and many other advantages. In domestic, at present, low frequency and high frequency RFID technology develops quickly, with the beginning of microwave band (2.45 GHz) research, the antenna as an important part of the RFID system, its has important theoretic and practical effects to research.In this paper, the tag antenna and reader antenna of 2.45GHz RFID systems has been studied, and the microstrip patch antennas and microstrip slot antennas are proposed as the models of antenna. The antenna's structure, working principle, and analysis method has been introduced, including transmission line analysis model and the principle of bawellnie methods. The performance parameters involved in the design process of the microstrip patch antennas and microstrip slot antennas has been analyzed and discussed.Secondly, the Genetic Algorithm(GA) is also studied in this paper, and according to the actually needs, presents a improvement plan:the Niche Genetic Algorithm(NGA) with elite protection strategy, and the numerical test and verify has been completed, And on this basis, combining the transmission line theory method, this paper analyzed the magnetic material and the effects of miniaturization microstrip antenna. The magnetic material also been one of the substrates, the 2.45GHz passive RFID tag antenna is designed. The antenna with a simple structure, easy to integrate. The antenna's size is 40mm* 30mm, also with good return-loss characteristics and directivity characteristics, the antenna's gain is 2.35 dBi, the bandwidth (S11<-10dB) is 70MHz, satisfied the RFID tag antenna working frequency.Finally, we studied reader antenna, the antenna's high-gain and the wideband characteristics are studied, several methods of acquire the antenna's high-gain and wideband are analyzied, and the metal-reflection-cavity and the microstrip slot antenna are proposed as the design model.The Multi-Objective Genetic Algorithm(MOGA) is adopted to optimize the antenna'size., in addition, the magnetic materials also be used to reduce the size of the antenna, a reader antenna working in the 2.45GHz is proposed, the proposed antenna fabricated by five layers, the size of the antenna is 150mm* 200mm, the gain is 10.9 dBi, the bandwidth of the antenna is 230MHz. And the antenna is fabricated and measureded, the measured results meet the requirements, and the antenna's reading distance is estimated, its reading distance is 28 meters, far from the existing 2.45GHz RFID system of reading distance. |
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