Microwave-Range Dielectric Characterization of Nematic Liquid Crystal Using Multisection Transformer Based on Two-Line Method

Multisection transformer (MST)-based sensors are proposed to measure the microwave-range dielectric properties of nematic liquid crystal (NLC) using the two-line method. Distinct from the typical two-line method employing transmission lines with unequal physical length, the proposed one adopts two sensors with identical physical sizes but filled with different dielectric materials (air and NLC SM52-2). Consequently, less NLC consumption is required. To compensate for the impedance mismatch arising from the large difference in dielectric constants between the two filling materials, the MST is designed. The proposed MST and MST-based sensors achieve reflection coefficients remain below -10 dB from 8 to 14.5 GHz over a wide range of relative dielectric constants from 1 to 5. The dielectric constants of NLC are extracted from the phase difference between the two sensors. The loss tangents are derived from the insertion losses. Compared with the reference values, the relative errors of the dielectric constant and loss tangent are within 3.77% and 63.33%, respectively.