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%.