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 TM11 and TM21 mode, as well as the orthogonal mode of TM11. The Gamma-shaped feed is employed to stimulate the TM21 mode. Besides, due to the parasitic radiation from the face-to-face Gamma-shaped feeds with opposite phase, the radiation peak of the circular patch under TM21 mode is along the broadside direction, which is different from the original radiation mechanism of TM21 mode. By loading shorting pins in the middle area of circular patch, the polarization orthogonal mode of the fundamental mode (TM11) 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 0.57 lambda(0) x 0.57 lambda(0) and the height is only 0.053 lambda(0) (lambda(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.