Y-type hexagonal ferrites for microwave absorber and antenna applications

This article examines the potential of the Y-type hexagonal ferrites, BaSrCo2−xNixFe12O22, as passive microwave absorbing materials and magneto-dielectric antenna substrates. To this effect, we investigated the electromagnetic properties of the fabricated samples up to 18 GHz, in conjunction with the composition, microstructure and static magnetic characteristics. It was found that the Ni substitution yields the increase of permeability μ* and permittivity ε* as a consequence of the weaker magnetocrystalline anisotropy and enhanced dielectric orientation polarization. By virtue of their different ε* and μ* spectra, the Co-rich hexagonal ferrites appear as appropriate for narrowband-yet tunable-reflection reduction in the 2.6-18 GHz range (>20 dB), whereas with Ni addition wideband attenuation of the transmitted waves (>20 dB) is attained in the 7-18 GHz band. In addition, the persistence of high refractive index up to 1 GHz enables the utilization of these hexagonal ferrites in UHF antenna designs with smaller dimensions. Among them, designs with Co2-Y compound are liable to higher radiation efficiency, while Ni2-Y favours the achievement of wider bandwidth. On this basis, the performance of the produced materials in high frequency applications is evaluated and certain improvement directions are indicated.