Circular polarized aperture coupled patch antennas for an RFID system in the 2.4 GHz ISM band

The design of aperture coupled patch (ACP) antennas for an RFID system in the 2.4 GHz ISM using circular polarization modulation is presented. Due to the requirements of the modulation scheme the ACP antennas are circularly polarized with switchable polarization sense. Four ACP antennas are compared according to their impedance and gain bandwidth, axial ratio, and crosspolarization isolation. Among the presented antennas a novel compact ACP antenna is shown that allows replacement of the conventional quadrature hybrid polarizer by /spl lambda//4 quarter transmission lines.