A Broadband UHF Near-Field RFID Antenna

A broadband segmented loop antenna is presented for ultra high frequency (UHF) near-field radio frequency identification (RFID) applications. Using a segmented line, the current distribution along the loop is kept in phase even though the perimeter of the loop is more than two operating wavelengths so that the proposed antenna generates strong and even magnetic field distribution in the near-field zone of the antenna. The antenna prototype, printed onto a piece of FR4 substrate, with an overall size of 175 x 180 x 0.5 mm(3), achieves a large interrogation zone of 154 x 154 mm(2) with good impedance matching and uniform magnetic field distribution over the entire UHF RFID band of 840-960 MHz.