Design of a Circularly Polarized Microstrip Patch Antenna with a Stacked Structure

In this study, a directly fed microstrip patch antenna with circular polarization was proposed, utilizing a stacked structure to enhance the impedance and axial ratio bandwidths. The proposed antenna consists of a driven patch antenna and a parasitic patch antenna with an air layer and a parasitic patch inserted between the lower and upper substrates to increase the impedance and axial ratio bandwidths. For circular polarization, the diagonal corners of the driven and parasitic patches were truncated and a cross-shaped slot was added inside the patches. The proposed circularly polarized antenna structure was fabricated and tested. Measurement results showed an impedance bandwidth below −10 dB ranging from 7.34 to 9.46 GHz, and an axial ratio bandwidth below 3 dB from 8.06 to 9.39 GHz.