A Low-Profile Circularly Polarized Conical-Beam Antenna with Wide Overlap Bandwidth

Abstract

In this paper, a low-profile circularly polarized (CP) conical-beam antenna with a wide overlap bandwidth is presented. Such an antenna is constructed on the two sides of a square substrate. The antenna consists of a wideband monopolar patch antenna fed by a probe in the center and two sets of arc-hook-shaped branches. The monopolar patch antenna is loaded by a set of conductive shorting vias to achieve a wideband vertically polarized electric field. Two sets of arc-hook-shaped parasitic branches connected to the patch and ground plane can generate a horizontally polarized electric field. To further increase the bandwidth of the horizontally polarized electric field, two types of arc-hook-shaped branches with different sizes are used, which can generate another resonant frequency. When the parameters of the arc-hook-shaped branches are reasonably adjusted, a 90° phase difference can be generated between the vertically polarized electric field and the horizontally polarized electric field, so that the antenna can produce a wideband CP radiation pattern with a conical beam. The proposed antenna has a wide impedance bandwidth ( $\mid S_{11}\mid <-10\text{dB}$ ) of 35.6% (4.97-7.14 GHz) and a 3 dB axial ratio (AR) bandwidth at $\text{phi}=0^{°}$ and $\text{theta}={35}^{°}$ of about 30.1% (4.97-6.73 GHz). Compared with the earlier reported conical-beam CP antennas, an important feature of the proposed antenna is that the AR bandwidth is completely included in the impedance bandwidth, that is, the overlap bandwidth of $\mid S_{11}\mid <-10\text{dB}$ and $\text{AR}<3\text{dB}$ is 30.1%. Moreover, the stable omnidirectional conical-beam radiation patterns can be maintained within the whole operational bandwidth.