Antenna Designs For Passive RFID Systems

RFID (Radio Frequency Identification) technology is a remote automatic identification technology, which enables target recognition and relevant data acquisition through radio frequency signals. In a RFID system, antennas, including tag antennas and reader antennas, are vital parts of the system and their performances greatly affect the reading range and accuracy of the RFID system. With the rapid development of RFID applications, more requirements for RFID antennas have been put forward, such as antenna miniaturization, new fabrication methods, multi-band and so on. Based on antenna and microwave circuit theories, design and new fabrication methods of RFID tag and reader antennas are studied in this thesis. The main academic contributions are summarized as follows.1. Two UHF RFID tags antennas fabricated in traditional technologies have been proposed. They are metal-insensitive RFID tag antenna with miniature meander-line impedance matching structure to tune the input reactance of the antenna and capacitively-loaded inductively-coupled fed loop antenna with an omnidirectional radiation. Based on the equivlent circuits, the working frequency and impedance matching of the loop antenna have been explained and the design procedure of the loop antenna has been summarized.2. Two tags antennas fabricated in advanced technologies have been proposed. They are inkjet-printed micro-fluid chipless tag antenna and 3D-inkjet-combined printed button-shaped tag antenna. The chipless antenna is based on traditional multi-resonators and micro-fluid channels are added to tune both resonate frequencies and frequency-based codes; the button-shaped tag antenna is a three-dimensional structure fabricated in 3D-inkjet-combined printing technology, with the advantages of compact size, portability, easier integration and high precision.3. A printed two dipole array antenna with a high front-to-back ratio is proposed for UHF RFID handheld readers. The proposed antenna is based on the Moxon antenna, and is a parasitic dual-element array with the ends of both elements folded back towards each other for additional coupling. It features a compact size and a considerable high front-to-back ratio. The design procedure of the reader antenna has been summarized.