Design and evaluation of HF/UHF dual-band RFID tag utilizing HF-coil as UHF antenna conductor

The demand for RFID tags that can be read by both HF and UHF RFID systems has been rapidly increasing. In this paper, we propose a novel HF/UHF dual-band tag antenna configuration that utilizes an HF coil conductor positively as a UHF antenna conductor. In order to control UHF current flowing on the coil and to achieve high radiation efficiency, the coil windings are coupled capacitively. The inductively coupled feed technique is adopted to obtain wider impedance bandwidth. It is shown by numerical electro-magnetic simulation that the fractional bandwidth of the actual gain of more than 1 dBi and 0 dBi are approximately 11% and 16%, respectively. The readable ranges of the prototype tag are 8-m and more than 10-cm in the UHF and HF, respectively.