In this paper, a low-profile and wideband circularly polarized patch antenna using four resonance modes is presented. It is one kind of four-port antenna implemented by loading five shorting pins on the circular patch. In order to achieve wideband properties, TM 11 and TM 22 modes are stimulated in circular patch, along with their polarization orthogonal modes (TM 11+ and TM 22+ modes). The TM 11+ mode is excited by the Γ-shaped feed, while the TM 22 mode and TM 22+ mode is stimulated by four shorting pins in close proximity to the Γ-shaped feed. Due to the strong coupling between shorting pins and Γ-shaped feed, the peak electric field generated on the two opposing shorting pins causes the magnetic current density on the circumference of the patch to be changed, which in turn leads to the realization of broadside radiation in the TM 22 and TM 22+ modes. In addition, the function of the shorting pin loaded in the center of the patch is to improve the impedance matching when TM 22 and TM 22+ modes are operated. Cooperated with the devised one-to-four feed network with equal amplitude and progressive phase difference of 90 , the wideband circularly polarized patch antenna is obtained. To verify this design concept, a prototype is fabricated and measured. The diameter of the patch is 0.68λ 0 and the profile is 0.078λ 0 (λ 0 is the wavelength in the free space at the center frequency). The measured relative bandwidth of VSWR < 2 is 106%, involving 1.53-4.96 GHz, while that of AR < 3 dB is 98%, ranging from 1.54 to 4.48 GHz. Besides, the measured LHCP gain > 3 dBic in the frequency band of 1.48-4.42 GHz.
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 halfwavelength cross-shaped slot, while the higher two modes are TM 11 mode and TM 31 mode of the circular patch, in which the TM 31 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 TM 31 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.
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