Dielectric permittivity measurement technique based on waveguide FSS filters

A hybrid resonant/transmission reflection method to determine the dielectric permittivity of materials is presented. The measurement procedure is based on the use of a low cost frequency selective filter transversally placed in a waveguide in the proximity of the unknown sample. The frequency selective surface and the dielectric sample constitute a resonant structure. As the dielectric permittivity of the sample is increased, the resonance frequencies of the transmission (or reflection) coefficient of the FSS are shifted. The relationship between the frequency shift and the permittivity of the dielectric under test allows the determination of the permittivity of the sample. Such procedure is particularly suitable for measuring the dielectric permittivity of thin slabs.