Matching, coverage and polarization optimization of UHF tag antennas for long range RFID applications

Resumen

Radio Frequency Identification (RFID) is becoming a widespread technology, e.g. for supply chain, tracking, inventory management and bioengineering applications. As RFID systems grow rapidly, the market demands more features such as longer range and increasingly cost-effective designs. Among RFID tags, Ultra High Frequency (UHF) passive alternative is the most promising, as they operate without battery and their very small size antenna can be used for several applications, like item tracking, especially useful for global supply chain management. Furhermore, new application possibilities have arised with the integration of ultra low consumption sensors into passive UHF RFID tags, such as patient temperature monitoring in hospitals, pressure monitoring in tires, strain monitoring in beams inside buildings ¿ Nevertheless, RFID vendors reproach that the business is not growing as fast as was expected at the beginning. The problem is that RFID technology is facing challenges for global adoption related to environment/platform impact, cost and orientation sensitivity between reader and tag. To give a solution to these problems, this doctoral thesis work is presented, where different RFID tag antennas that address the presented problems are shown: a compact RFID dipole that could be matched to any arbitrary RFID IC, a cross dipole tag antenna with circular polarization which has a wider coverage to its linearly polarized counterpart and a PIFA antenna that performs as an on-body antenna. Furthermore, to study the influence of different platforms on a RFID tag, the compact RFID tag is placed onto a non-metallic, water filled and metallic platform as representatives of most kind of materials. In the same way, a methodology to characterize a frequency-dependant minimum size platform representative of a larger one is presented. This platform aims to analyze its impact on a RFID tag for electrically large materials. To complete these designs and studies, practical methods to obtain various parameters like dipole antenna impedances, circular polarization patterns and read ranges will be explained. This work was carried out to work under the UHF RFID European legislation by ETSI.