Design of a microwave variable delay line using liquid crystal, and a study of its insertion loss

A microwave variable delay line was designed and fabricated using a nematic liquid crystal for the dielectric substrate of the microstrip line, and the phase characteristics and insertion losses of the device were evaluated. The phase shift characteristics were found to be in close agreement with the design value, indicating the ability to implement wide‐band variable delay lines over a microwave frequency range. The insertion losses of the fabricated variable delay line were found to be too high for practical applications, and it was revealed that the losses were dominated by conductor losses. It was found that one effective way to reduce losses was to increase the thickness of the liquid crystal layer, but this had the negative effect of making the response time of the liquid crystal alignment slow. It is thus critically important in designing liquid crystal variable delay lines that careful consideration be given to the trade‐off between insertion losses and response time depending on the application.