Compact Wideband Circularly Polarized Quarter-Mode Substrate Integrated Waveguide Antenna for Low-cost 2.4 GHz RFID Reader

Two circularly polarized (CP) microstrip antennas based on quarter-mode substrate integrated waveguide (QMSIW) are proposed. These two antennas are designed for a low-cost miniaturized RFID reader with a targeted centre frequency of 2.44 GHz, and are required to be fitted in a relatively narrow 58×22 mm area fully backed by metal ground using a 1.7 mm (0.014 λ
0
) thick FR-4 PCB substrate. Both antennas employ a structure with dual QMSIW radiator, which can fully utilize the aperture area and achieve a decent gain and efficiency. The first antenna achieves a measured −10 dB impedance bandwidth of 3.5%, a 3 dB AR bandwidth of 0.82%, and in-band realized peak gain of −0.2 dBic. While the second antenna achieves a large enough measured −10 dB impedance bandwidth of >30%, a 3 dB AR bandwidth of 6.4%, and in-band peak gain of −0.9 dBic. The compatibility with low-cost substrate and processing, and adequate performance make these antennas well suited for low-cost miniaturized RFID readers.