Potential applications of nematic liquid crystal materials in the millimeter wave region

Abstract

Large tunable properties induced by the change of LC molecular orientation states can be expected for wider frequency region except for visible rays. Focusing on the millimeter wave (MMW) region, a novel measurement method for LC materials is investigated using the rectangular waveguide test cell and several commercially available nematic LC materials have been actually evaluated for V-band (50GHz-75GHz) and W-band (65GHz-110GHz) regions. Refractive indices for the direction parallel to the LC molecular orientation in the MMW region are almost the same with those in the visible rays, on the other hand the indices for the direction perpendicular to the LC orientation show a little larger values. Consequently, refractive index anisotropy which is the most important for the tunable LC devices reduces to be 1/2 through 1/3 of that in the visible rays. Although the larger refractive index anisotropy is desired for the better performance, the anisotropy of the usual LC materials is still large and the loss properties are fairly good. Based on the materials data, we have demonstrated the CPW type LC devices combining with an ITO glass substrate on it. Phase and amplitude changes of the transmitted MMW by the LC driving are investigated considering the influences of some device parameters.

Liquid-crystal-based floating-electrode-free coplanar waveguide phase shifter with an additional liquid-crystal layer for 28-GHz applications

“…The conventional LC-based floating-electrode (FE)-free CPW has the advantages of low manufacturing cost and easy fabrication process, but its tuning range (TR) is too small because the LC is only between the electrodes of CPW [15]. To expand the TR, CPWs that include an additional FE have been studied [16][17][18][19]. Although we can improve the TR with FE structure, they are more complex.…”

Recent measurements of compact electronically tunable liquid crystal phase shifter in rectangular waveguide topology

“…Introduction: Developments in liquid crystal (LC) based tunable components are ongoing. Typical planar structures have been presented in the past [1,2]. Previously, an efficient topology for LC phase shifters (LC-PSs) has been proposed [3].…”