Electrically large dual-loop antenna for UHF near-field RFID readers

A dual-loop antenna is proposed to enlarge the interrogation zone of reader antennas used in near-field ultra high frequency (UHF) radio frequency identification (RFID) systems. The dual-loop antenna is composed of two segmented loos with one common side and a double-sided parallel-strip line feeding network. Each loop has a uniform and single direction flowing current itself. By providing reverse-direction flowing current to the two segmented loops, the strong and uniform magnetic field distribution over a large interrogation zone can be achieved. The prototype on FR4 printed borad (PCB) exhibits that the dual-loop antenna achieves the impedance matching over the frequency range from 790 to 1040 MHz and produces strong and uniform magnetic field distribution over an interrogation zone of 308 mm × 150 mm.