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 performance 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 a stable reading performance, but also reduce the antenna's length. The proposed tag antenna maintains a small size with a diameter of 10 mm (0.031 lambda) and a length of 45 mm (0.137 lambda). With an effective isotropic radiated power (EIRP) of 4W, 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 a metal surface. The tag has the advantages of a more compact size, better reading range, and excellent rolling capability on a metal surface in comparison with the state-of-the-art. These features fulfill the emerging demands in the industrial Internet of Things field.