Analysis of Low Profile UHF RFID Tag Antennas and Performance Evaluation in Presence of a Metallic Surface

Passive UHF RFID systems have drawn considerable attention because these can provide a long reading range, high data rate and small antenna size. However, a passive UHF RFID system has challenges in tagging a metallic object due to the effects of conducting materials on the tag antenna performance. This paper proposes two widely used label-type antennas: folded dipole antenna and meandered dipole antenna to optimise design parameters such as impedance matching, feeding techniques, size-reduction, bandwidth etc. The proposed low profile antennas can operate at 866 MHz which is suitable for the UK and Europe UHF RFID frequency band. The paper also presents an investigation and analysis of the effects of a metallic surface on the performance of the proposed dipole tag antennas. It studies the effects of distance between the metal and the tag, thicknesses of the metallic plate and antenna substrate. The performance is evaluated in terms of return loss, shift in resonance frequency and bandwidth. The simulation results show that when the tag antennas are mounted closer to a metallic surface, the return loss of the tag antennas is significantly increased and the resonance frequency is also shifted from the desired operating frequency. Although the size is reduced, these antennas might not be good choices for tagging metallic objects. An antenna that uses metallic surface as the ground plane e.g. Micro-strip patch antenna and planar inverted-F antenna (PIFA) might be a possible solution in this case.