Wide axial-ratio bandwidth crossed dipole RFID antenna

A circularly polarised RFID tag antenna with wide axial ratio bandwidth, wide impedance bandwidth and simple tuning network is presented. The antenna, based on the widely used crossed-dipole design, incorporates a novel matching network based on two large L-shaped strips joining the arms of the dipoles to match the impedance. The L-shaped strips create large area loops enabling the antenna to be adapted to the high inductances required for good matching without the currents flowing through them degrading the axial ratio of the antenna. The gain pattern, input impedance and axial ratio (AR) are computed with numerical simulation and measurements, resulting in a 30 MHz bandwidth based on the -3 dB Axial Ratio criterion, which can provide a maximum reading distance of 12.8 m.