Low-Profile and Wideband Unidirectional Antenna With Ferrite Loading for UHF Applications

A low-profile and wideband unidirectional antenna with ferrite loading is presented for ultrahigh-frequency (UHF) applications. This design comprises a slotted bowtie antenna with parasitic elements placed 50 mm over a ground plane. A small amount of ferrite loaded on the center of the ground plane plays a crucial role in improving the performance of the low-profile antenna. The ferrite used here is a new type of magnetodielectric material with relatively high permeability and permittivity, as well as low magnetic and dielectric loss. The loaded ferrite introduces an additional phase change of the electromagnetic field reflected by the ground to improve the impedance matching, bandwidth, efficiency, and gain of the low-profile antenna. The evolution process and mechanism of the proposed antenna are elaborated. For validation, an optimized antenna prototype was fabricated and measured. The measured results are consistent well with their simulations, which shows the realized gain of 7.2–9 dBi over
$\vert \text{S}_{11}\vert \le -10$
dB impedance bandwidth of 38% (480–705 MHz). The overall profile of this antenna is only
$0.08\lambda _{0}$
, where
$\lambda _{0}$
is the free-space wavelength at the lowest frequency of operation.