Complex permittivity measurements with a low cost parabolic resonant cavity

A low-cost Fabry Perot open resonator is used to measure the complex permittivity of flat sheets of dielectric materials in the X-band. The method is based on the measurement of the resonant frequency shift of the fundamental mode, described by the Gaussian beam theory. Instead of spherical mirrors, conventionally used for open resonators, the cavity is formed by parabolic reflectors, originally intended for satellite communications, reducing the production costs. A technique to improve the sample alignment is introduced, and to validate the results of the parabolic cavity, the relative permittivity and loss tangent of three different samples are measured.