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 (∣S11 | <−10 dB) of 35.6% (4.97‐7.14 GHz) and a 3 dB axial ratio (AR) bandwidth at phi = 0° and 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 ∣S11 | <−10 dB and AR < 3 dB is 30.1%. Moreover, the stable omnidirectional conical‐beam radiation patterns can be maintained within the whole operational bandwidth.