Characterization of Nematic Liquid Crystal at Microwave Frequencies Using Split-Cylinder Resonator Method

Liquid crystal (LC) is an anisotropic liquid material, which flows like a liquid, but at the same time, its molecules have an orientational order like in the solid state. Thus, LC is a promising dielectric material for designing reconfigurable devices at microwave frequencies. In order to optimize the design of reconfigurable microwave devices, accurate values of the dielectric permittivity and the loss tangent of LCs are needed. However, new LCs are not well characterized at these frequencies because of its recent use for microwave applications. Therefore, the characterization in this frequency range is required for its practical use within microwave components and devices. In this paper, a split-cylinder resonator method is used for the characterization of four different nematic LCs at two frequency points, i.e., 5 and 11 GHz. This characterization includes the extraction of their complex dielectric permittivity values at these frequencies. The employed method allows to obtain the two extreme permittivity values without applying any external electric or magnetic field to polarize the LC molecules. Two different approaches, a modal analysis method and a full-wave numerical technique, have been used for determining the LC parameters obtaining similar results in both cases.