Double-layer folded loop antenna for UHF near-field RFID applications

In this paper, a double-layer folded loop reader antenna is proposed for ultrahigh frequency (UHF) near-field radio frequency identification (RFID) applications. The current distribution along the top loop is kept in phase by folding the microstrip line down to the bottom layer. Thus, the proposed antenna generates strong and even magnetic field distribution in the near-field zone of the antenna. The antenna is printed on two sides of FR4 substrate, with the diameter of 94mm and the height of 20.2mm. The antenna achieves good impedance matching and uniform magnetic field distribution over the band of 858MHz~869MHz. In addition, the simulated reading distance is 90mm.