Wideband and Low-Profile Omnidirectional Circularly Polarized Antenna With Slits and Shorting-Vias

A novel wideband and low-profile omnidirectional circularly polarized (CP) patch antenna is proposed. The antenna is constructed on a via-shorted circular patch with slits cut on the bottom and top planes. By loading vias on the circular patch antenna, the TM
₀₁
mode is generated and coupled to the original TM
₀₂
mode. Then, a wide bandwidth is achieved. Moreover, the asymmetrically placed slits will generate a horizontal polarization, while the nonslit monopolar antenna will provide a vertical polarization. With a quadrature phase difference and equal amplitudes for the two orthogonal polarizations, a CP radiation could then be obtained. A prototype is fabricated and measured. With a low profile of 0.028λ
₀
, the antenna has a 10-dB return-loss impedance bandwidth of 16.6% and a 3-dB axial-ratio bandwidth of 14.8%.