Research On UHF Near-Field RFID Reader Antennas

Radio Frequency Identification(RFID) is a contactless automatic identification technology using radio frequency signal for data communication. In recent years, with the rapid development of microelectronics, integrated circuits and information security technology, RFID technology begins to get rid of the obstacle of high cost. Nowadays, RFID has been widely used in food safety detection, medicine monitoring, supply chain management and retail industry.UHF near-field RFID technology can not only transfer data in high speed, but also perform excellently in complex surrounding environment. Thus, it has wide application potential in item-level identification. This dissertation has designed three novel UHF near-field RFID reader antennas, and the main contributions are summarized as follow:1. A UHF near-field RFID reader antenna based on segmented lines is proposed in this paper. This antenna has a compact size of 90×77×1mm3. The measured results show that the antenna has a 10-d B impedance bandwidth of 130 MHz. With 30 dBm input power, the maximum reading distance is 155 mm, and within the height of 115 mm the antenna can achieve a 100% read percentage. By tuning several parameters, the broadband antenna can perform well in near-field with different size of interrogation zone.2. In this paper, a UHF near-field RFID reader antenna based on microstrip slot structure is proposed. By adapting segmented lines and cutting slots on the ground plane, the antenna works in the band of 850-970 MHz and achieves a strong and uniform magnetic field in the near-field zone. With 30 dBm input power, the maximum reading distance is 120 mm, and the interrogation zone is 160×160mm2 at a height of 20 mm.3. Multiband RFID antennas allow the RFID system to work in different applications. In this paper, a compact multiband RFID antenna for near-field and far-field operations is presented. It is composed of three coupling structures: a meandered line, an inverted-L structure and a U-shaped structure. In the 920-925 MHz and 2.4-2.48 GHz, the antenna works both in near-field and far-field, while in 5.815-5.875 GHz, the antenna works in far-field.