Design And Measurement Of Rfid Metal Tag Antenna

Radio frequency identification technology (RFID) is a non-contact automatic technology, in recent years, which is gaining popularity for efficiently tracking and managing of objects in logistics and pharmaceutical industry. This technology is more convenient than the use of bar codes and optical scanners. And the UHF RFID system operates at the bands of North and South America (902-928MHz, FCC band), China (840-845MHz and920-925MHz) and Europe (865-867MHz). The tag antenna plays the key role in the RFID system, and it is commonly designed in the commercial domain as a dipole type with linear polarization (LP) in the UHF-band. However, only half of the power transmitted by the reader antenna is received because of the polarization efficiency is-3dB if the RFID reader antenna is designed with CP polarization. In order to maximize the power transfer and the reading range, a novel circularly polarized annular-ring RFID tag antenna which is fed by electromagnetic coupling is proposed here. Due to the read range performance of metal tag antenna in free space is small, a robust antenna is proposed in this paper that operates as a dipole when in free space, but when placed on a conducting surface, it operates as a relatively efficient microstrip antenna.Currently, the read range and the impedance of the UHF RFID tag antenna are two important measurement parameters. Because of the impedance of the chip impedance with reactance part, considering the conjugate match, the tag antenna impedance is complex. The way to measure the impedance matching of the antenna impedance accurately is a big problem. A coaxial cable from the power supply are unbalanced way, resulting in the current antenna on different arms, we cannot get accurate data of antenna impedance. To solve this problem, we propose a two-port antenna impedance measurement based on vector network analyzer port extension functionality. In the read range measurement direction, we built a tag read range measurement platform based on Friis transmission formula.