A wideband circularly polarized patch antenna based on TM 31 mode and slot mode

A wideband circularly polarized patch antenna is presented in this article. The four-port antenna is composed of circular patch loaded with four shorting pins and cross-shaped slot. The realization of wideband benefits from the cooperation of three resonant modes. The lowest mode is due to the resonance of half-wavelength cross-shaped slot, while the higher two modes are TM11 mode and TM31 mode of the circular patch, in which the TM31 mode is excited by loading four shorting pins. The L-shaped probes are utilized to establish the coupling feed mechanism for impedance matching in a wideband range. And the compensation of the radiation null in the broadside direction benefits from the variation of the electric field distribution caused by the shorting pins and the differential L-shaped feed structure in TM31 mode. For the aim of implementing circularly polarized radiation in the proposed patch configuration, a phase quadrature feed network consisting of power dividers and phase shifters is designed and cooperated with this antenna. In order to verify the design concept, a prototype has been fabricated, assembled and measured. The measured results show that the relative bandwidth of VSWR <1.7 and AR <3 dB is 66.7%, ranging from 2 to 4 GHz. In addition, the measured LHCP gain >3 dBic within 2.01–3.84 GHz, and the fractional bandwidth is 61%. Moreover, the peak gain is 9.9 dBic.