A Low-Profile and Wideband Circularly Polarized Patch Antenna Based on TM11 and TM21

In this article, a low-profile and wideband circularly polarized patch antenna is proposed and developed, which is composed of the circular patch fed by four ports. A wideband property is achieved by utilizing TM
₁₁
and TM
₂₁
mode, as well as the orthogonal mode of TM
₁₁
. The Γ-shaped feed is employed to stimulate the TM
₂₁
mode. Besides, due to the parasitic radiation from the face-to-face Γ-shaped feeds with opposite phase, the radiation peak of the circular patch under TM
₂₁
mode is along the broadside direction, which is different from the original radiation mechanism of TM
₂₁
mode. By loading shorting pins in the middle area of circular patch, the polarization orthogonal mode of the fundamental mode (TM
₁₁
) is excited properly, which contributed to bandwidth enhancement. Cooperated with the quadrature phase feed network, a wideband circular patch antenna with unidirectional radiation and circular polarization properties is designed, fabricated, and measured. The size of the circular patch is 0.57λ
₀
×0.57 λ
₀
and the height is only 0.053λ
₀
( λ
₀
is the free space wavelength at the center frequency). The measured results show that the 109% of fractional bandwidth is obtained under the condition of VSWR <; 2, ranging from 0.94 to 3.18 GHz, and the 3 dB axial ratio fractional bandwidth is 95%, ranging from 1.04 to 2.93 GHz. Besides the realized LHCP gain >3 dBic from 1.27 to 2.99 GHz.