Measurements of complex permittivity and permeability of common ferrimagnets at millimeter waves

In this paper, complex permittivity and permeability of several yttrium iron garnet (Y]G) and hexagonal ferrite ceramics are investigated in a broad-band spectrum for the first time. The measurements were realized using a broad-band quasi-optical millimeter-wave (QOM) system with a backward-wave oscillator as the source of tunable coherent radiation. The dielectric and magnetic parameters of the ferrimagnets were obtained by fitting theoretical curves to the experimental spectra. Three types of YIG specimen were initially measured and compared to theoretical results, and then hexagonal ferrites were measured in the demagnetized state for the first time. It was shown that this method provides an accurate characterization of soft ferrites as well as hard anisotropic ferrites in the entire millimeter-wave range.