A Compact Circularly Polarized Crossed-Dipole Antenna for an RFID Tag

A compact circularly polarized (CP) crossed-dipole antenna for radio frequency identification in the ultra-high frequency is proposed. The antenna consists of two orthogonal dipoles with an arm composed of a meander line and triangular-shaped ending for achieving a compact size. A modified T-match with a meander line is used for impedance matching between the antenna and the tag chip. In this design, CP excitation is achieved by incorporating two semi-circular curves inserted between the orthogonally arranged dipole arms. The final design, with the dimensions of 35.6 x 35.6 x 0.508 mm(3), yields a -10-dB impedance bandwidth of 37 MHz (892-929 MHz) and a 3-dB axial-ratio bandwidth of 11.4 MHz (905.2-916.6 MHz). The measured results show that the proposed tag antenna can provide a maximum reading distance of approximately 7.6 m with an effective isotropic radiated power of 3.28 W over the CP operational bandwidth.