Resonant determination of the dielectric properties of materials in the microwave range

This paper describes the determination of the complex permittivity of dielectric materials in the Ku-band. For the determination of the real part of the permittivity a section of a rectangular cavity resonator is filled with the unknown material. The reflection coefficient of this loaded cavity setup is measured by a vector network analyzer. From the measured resonant frequency the real part of the permittivity can be calculated using a 3D FDTD field solver and an interpolation technique. In order to determine the loss tangent two identically shaped cavities are used, one made of copper and another one made of brass. The reflection coefficient of both types of cavities is measured twice namely with and without dielectric load. Applying this method it is possible to distinguish between the ohmic losses of the cavity and the dielectric losses of the sample. Experimental results are presented for PTFE and AK4.