A small RFID tag antenna to identify metallic objects

This letter presents the design of a small and low-profile RFID tag antenna in the UHF band that can be stuck to metallic objects. The designed tag antenna which uses a ceramic material as an antenna substrate consists of a radiating patch and microstrip lines for a proximity-coupled feeding structure, which is the structure that can easily obtain impedance matching between an antenna and a tag chip without any additional matching network. The fractional return-loss bandwidth for S₁₁<10 dB and radiation efficiency are about 1% and 40% at 911 MHz, respectively. The read range is approximately from 3 to 4 m when the tag antenna is mounted on a metallic surface.