Methods for improving the tuning efficiency of liquid crystal based tunable phase shifters

This paper presents the methods how to use material tunability efficiently in order to improve the tuning efficiency of a phase shifter. The tunability is achieved by using anisotropic liquid crystal (LC) material. Parameters affecting the tuning efficiency of a transmission line type and of a periodically loaded transmission line type phase shifters are discussed. Based on these results, a tunable phase shifter with a figure of merit 90°/dB at 18 GHz and a LC varactor operating at 30 GHz are realized. Measurement results of the scattering parameters and tuning speeds of the prototypes are presented for different LC mixtures.