Ceramic patch antenna using inductive coupled feed for UHF RFID tag mountable on metallic objects

A small UHF band RFID tag antenna using ceramic material mountable on metallic surfaces is presented. The size of the proposed tag is 25 mm times 25 mm times 3 mm. The impedance of the antenna can be easily matched to the complex conjugate of the tag chip impedance by adjusting the size of the feed loop and the shorting plate of the side patch or the position of the feed loop. The maximum reading distance of the tag was 6 m when it was mounted on a 400 mm times 400 mm metallic surface. The proposed design is verified by simulation and measurements which show good agreement.