A low-cost, wideband RFID tag antenna on metallic surfaces using proximity-coupled feed

A low-cost, wideband antenna for radio frequency identification (RFID) tags mountable on metallic surfaces is presented. A novel proximity-coupled feed structure, in which the direction of the microstrip feedline is parallel to that of the resonant length of the radiating patch and one end of the feedline is shorted to the ground, is proposed to perform simple and wideband impedance matching between an antenna and a tag chip without any additional matching networks. The proposed design is verified by simulation and measurement. The measured 3 dB return loss bandwidth is about 49 MHz, which totally covers the 26 MHz bandwidth requirement in North America.