Design Fundamentals and Advanced Techniques of RFID Antennas

Abstract

The demand on the automated supply chain and logistics has been pervasive, aiming to replace the tedious bar-code labeling, and has driven an increasing number of research activities on the RFID to alternative and trustworthy solutions. The RFID takes the reader-and-tag paradigm where the interrogator(reader) uses its ‘remote’ correspondent(tag)s. To be sure about the reliable performance of an RFID system, though microelectronics for chip making and data acquisition are important, the antenna technologies for excellent wireless linkage have highly critical importance. When it comes to the tag and reader antennas for the RFID, designers adopt the concept imitating the radar technology in which the reader transmits a signal to a tag and the tag sends back its recorded data to the reader. The considerations must be made with the frequency, the impedance of the chip and antenna, the constraints(overall size), the radiation pattern and gain, the reading range, and the tagged objects(geometry and materials). Especially, care must be taken of with regard to the realistic environment that affects the near-field region of reader- and tag antennas and the operational quality of the overall RFID system[1-10]. Prior to the design of the reader- and tag antennas, the basics of antennas are tapped to see the way the electromagnetic fields propagate from radiators for higher frequency regimes (860MHz-960MHz) along with the magnetic- and electric coupling mechanisms for lower frequency(125kHz-134kHz). And then as the first place in the UHF-band RFID antenna design, the impedance matching techniques are addressed with a variety of antenna structures apt to the size reduction and acceptable efficient radiation. In particular, a couple of design examples are practiced with the illustrations obtained by the electromagnetic field solver. As a matter of course, this is accompanied by the considerations of the tags’ materials and relevant electromagnetic properties. And the advanced design schemes are introduced with the on-going topics such as multiple aspects in band and polarization as well as near-field UHF tags. It is followed by the remarks on the testing methodology of tag antennas’ input impedance, gain, pattern and reading distance. Finally, conclusions are presented.