A UHF RFID Tag Antenna Placeable on a Metal Surface Without Degraded Performances

An ultrahigh-frequency (UHF) radio frequency identification (RFID) tag antenna that can be placed on a metal surface with stable performances is proposed. It is made of a modified dipole with two cylindrical metal grounds on both ends. The cylindrical metal grounds not only enable the antenna to roll freely on a metal surface with the stable reading performance, but also reduce the antenna's length. The proposed tag antenna maintains a small size with the diameter of 10 mm (0.031λ) and the length of 45 mm (0.137λ). With an effective isotropic radiated power (EIRP) of 4 W, experimental results demonstrate that the proposed tag can achieve a maximum read distance ranging from 9.1 to 11.7 m when the tag rolls on metal surface. The tag has the advantages of more compact size, better reading range, and excellent rolling capability on a metal surface in comparisons with the state-of-the-art. These features fulfill the emerging demands in the industrial internet of things field.