Analysis of Wideband Circularly Polarized Ferrite-Loaded Antenna Based on Unidirectional Resonant Modes

Abstract

We propose a wideband circularly polarized antenna that consists of a metallic patch and some parasitically coupled elements mounted on a grounded dielectric-ferrite substrate. The metallic patch is fed by a proximity-coupled feed line placed between the ferrite and the dielectric layers. The parasitically coupled elements are included to improve the impedance bandwidth of antenna and are excited through the metallic patch. The antenna utilizes the resonant modes of the structure, which rotate only in the clockwise or counter-clockwise direction. A semi-analytical solution based on the magnetic wall approximation shows that the resonance frequencies of the clock- and counter-clockwise resonant modes differ significantly when operating in the frequency range where the effective permeability of the ferrite layer is negative. Moreover, there is a good agreement between the model presented and full-wave numerical simulations. For the proposed antenna, the results show that the radiation bandwidth is more than 15.5% and the 3 dB axial ratio bandwidth is more than 50%. The proposed antenna is easy to design and fabricate, does not require a complicated feeding network, and has a wideband and wide-angle circular polarization.