Design of a broadband circularly polarized UHF RFID tag antenna for metallic objects

A novel UHF RFID tag antenna with broadband and circularly polarized feature has been proposed for metallic object application. Double-point orthogonal coupling feed technology utilizes two microstrips with the differ of a quarter-wavelength and loading cross-slot on the quasi-square radiation patch. Finally the tag antenna achieves 38 MHz and 16.2 MHz for the 3dB impedance bandwidth (898MHz-936MHz), the 3dB axial ratio bandwidth (913.8MHz-930MHz) respectively. Obviously, the result has covered the upper band (920MHz-925MHz) of local China RFID technology standard and the proposed tag antenna can keep stable read-write performance when mounted on different size of metal surface.