High frequency ratio antenna for RFID tags

Abstract

A novel high frequency ratio of about 180 for dual-frequency radio frequency identification (RFID) antenna with two different operation mechanisms (near field and far field operation) is proposed. The proposed antenna is obtained by printing a rectangular-spiral-shaped and a meander-shaped line, which is placed above on a rectangular microwave substrate as a RFID tag's antenna where its ground plane is at the bottom of substrate. The proposed antenna is fed by a 50 Omega microstrip line printed on the same substrate, and the antenna's two resonant frequencies can be excited with good impedance matching. Closer to omni-directional radiation patterns and the lower cross-polarization levels (at least 25-dB) are also obtained