A slim wideband patch antenna designed for the ultra-high frequency (UHF) band radio frequency identification (RFID) tag is presented in this paper, which can be mounted on flat or curved metallic surfaces directly. The presented antenna is fabricated on a very thin (only 0.5 mm) PET substrate (εr=3.8, tanδ=0.02). The proposed design consists of tow coplanar patches which are electrically connected to the metallic ground through two symmetrical shorting walls. Double symmetrical U-shaped slots are etched out to improve the antenna bandwidth. A perfect matching between antenna and tag chip can be obtained by varying the geometry parameters of the slots. The simulated bandwidth is about 97 MHz, which covers the Europe and North America UHF RFID frequency range. The measured maximum reading range of the proposed antenna can be up to 5 m when the tag is mounted on a metal plate whose size is 150×150×8 mm3.
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