A Low-Profile Ferrite-Loaded Crossed-Dipole Antenna with Wide Axial Ratio Bandwidth

Abstract

A low-profile ferrite-loaded crossed-dipole antenna with wide axial ratio (AR) bandwidth is suggested for UHF applications in this paper. The antenna consists of four sequentially rotated duplicate slotted trapezoidal patches etched on the top side of the FR4 substrate. The wide right-handed circular polarization AR bandwidth is achieved by feeding the crossed dipole through four cylindrical probes which transmit four equal-amplitude 90° phase shift signals (0°, 90°, 180°, and 270°). To achieve low profile, novel magneto-dielectric material which has relatively high permeability and permittivity is introduced to overcome the negative effects of ground plane. According to the simulated result, the suggested crossed-dipole antenna possesses a low profile of 49.7 mm (around <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0. 11\lambda_{0}$</tex> at the lowest frequency of 680 MHz) and exhibits the impedance bandwidth <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\vert \mathbf{S}_{11}\vert &lt; -10\mathbf{dB})$</tex> of 30% (680–920 MHz), the AR less than 1 dB across the operating band, and the peak gain of 5.77 dBi.