Radiation characteristics of circularly polarized patch antennas mounted in a 2.45 GHz wireless ID card system

A 2/spl times/2 circularly polarized patch antenna array is developed for the realization of noncontact data transfer between the ID card and the transmitter for a 2.45 GHz wireless ID card system. A digital phase shifter using PIN-diodes is inserted between two paired antenna elements to adjust its radiation beam compatible with application environments. Radiation characteristics with the axial ratio less than 0.5 dB and the beam shift with about 17/spl deg/, and return losses lower than -25 dB have been achieved experimentally.