A Differentially Fed Wideband Circularly Polarized Antenna
This study proposes a differentially fed circularly polarized (CP) antenna with common-mode (CM) suppression and a broad axial-ratio (AR) bandwidth for unidirectional radiation. First, the proposed antenna applies two crossed dipoles and two annular delay-line phase shifters to achieve circular polarization. Second, parasitic patches are used to broaden the AR bandwidth. Third, the crossed dipoles of the proposed antenna can be effectively excited under differential-mode operation, but not under CM operation; therefore, the antenna shows good CM suppression. The simulated results indicate that the proposed antenna has a 3 dB AR bandwidth of 31% (0.64 GHz, 1.74–2.38 GHz) at a CP center frequency of 2.06 GHz, and a wide –10 dB impedance bandwidth of 60.5% (1.30 GHz, 1.50–2.80 GHz) centered at 2.15 GHz. Besides, the CP antenna achieves stable radiation patterns and stable half-power beamwidths of <inline-formula><tex-math notation="LaTeX">${\text{69}}^\circ \,\pm \,{\text{2}}^\circ $ </tex-math></inline-formula> at the <italic>xoz</italic> plane and <inline-formula><tex-math notation="LaTeX"> ${\text{68}}^\circ \,\pm \,{\text{2}}^\circ $</tex-math></inline-formula> at the <italic>yoz</italic> plane. A prototype is fabricated and tested. The measured results are in a good agreement with the simulated results.