Miniaturized Metal-Mountable U-Shaped Inductive-Coupling-Fed UHF RFID Tag Antenna with Defected Microstrip Surface

Abstract

This study presents a novel miniature ultra-high frequency (UHF) radio frequency identification (RFID) tag for metallic objects. Its arrangement includes a U-shaped feeder, which is inductively coupled to two E-type connected patches. Size reduction is achieved by means of utilizing the U-shaped feeder, and introducing a defection in the connection between the two E-type patches. The defection in the connection area between the patches modifies the current distribution by increasing the electrical length, and the antenna inductance. Furthermore, increasing the length of the U-shaped structure significantly raises the antenna inductance and, consequently, the flexibility of the structure for the impedance matching purpose. Polytetrafluoroethylene (PTFE) is employed for the fabrication of the designed tag. The tag's size is 65 mm × 20 mm× 1.5 mm , and does not require any complex fabrication process such as utilization of metal vias and/or shorting stubs. It is observed that with 4W EIRP, the measured detection distance is 6.9 m when it is attached onto metal sheets ( 20 cm × 20 cm ), and 5.54 m when it is in free space. The measurement results also are in good agreement with the simulated results.