The gyrotropic and magneto-optical properties of a commercially available \(SrFe_{12}O_{19}\) hard ferrite material are investigated for the first time in the Ka-band (26.5−40 GHz), at frequencies well below the intrinsic ferromagnetic resonance of the material. Using a vector network analyzer and quasi-optical measurement setup, the complex permeability tensor and permittivity of the ferrite are determined, including the estimation of uncertainties. The frequency dependence of the material parameters is analyzed to characterize the hard ferrite for potential applications in quasi-optical Ka-band circulators. The results reveal that while dielectric losses remain low throughout the band, permeability losses become dominant in the upper half of the Ka-band, as the frequency approaches the magnetic resonance. This results in high attenuation and a pronounced frequency dependence of the Faraday rotation, which limits the usable bandwidth at higher frequencies of circulators utilizing this ferrite. In the lower half of the Ka-band, the frequency dependence is reduced, and the material exhibits low attenuation, making it promising for broadband quasi-optical nonreciprocal devices in this frequency range. These findings highlight both the potential and the limitations of the investigated hard ferrite for Ka-band quasi-optical components operated below the ferromagnetic resonance.
