Highly-anisotropic liquid-crystal mixtures for tunable microwave devices

Progress in the microwave dielectric properties of novel liquid crystal (LC) mixtures is reported, specially designed for voltage-tunable microwave devices. These advanced mixtures possess much higher microwave dielectric anisotropy and much lower loss tangent than standard LC substances such as K15 of Merck. Moreover, with Δn=0.37 at 26 GHz those novel LC mixtures exhibit by far the highest microwave anisotropy at room temperature, known from literature. Compared to a former approach with K15, the figure-of-merit of a tunable microstrip-phase shifter device has been increased significantly from 20°/dB up to 110°/dB, both measured at 24 GHz. To the authors knowledge, this is the best value demonstrated for a tunable phase shifter based on nonlinear dielectrics above 20 GHz, up to now. This substantial progress opens up totally new low-cost LC applications beyond optics.