UWB UHF RFID TAG antenna with branch-line slots for metallic objects

A novel UWB ultrahigh frequency (UHF) radio frequency identification (RFID) tag antenna designed for metallic objects is proposed, which is fabricated on a flexible polyethylene terephthalate substrate for low-cost production, whose relative permittivity is 3.8 and dielectric loss tangent is 0.02. The overall size of the proposed tag antenna is 56 x 10 x 0.8 mm(3). It consists of two coplanar patches which are electrically connected to the metallic ground through two symmetrical shorting walls placed at both edge sides of the patches. The resonant frequency can be adjusted by changing the shorting wall length. Double-symmetrical branch-line slots are created to improve the antenna bandwidth. The simulated bandwidth is about 223.5 MHz, which covers the global UHF RFID frequency range. The experimental results show that the maximum read range of the proposed antenna is larger than 2.6 m when it is mounted on a test metal plate with a size of 150 x 150 x 8 mm(3). (c) 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1689-1691, 2014