A Comparative Study of Paraelectrics and Novel Liquid Crystals for Tunable Microwave Devices

摘要

Two kind of tunable dielectrics are investigated and compared with respect to their microwave dielectric properties and their application potential in tunable microwave phase shifters: (a) ParaElectric (PE) thick films and (b) nematic Liquid Crystals (LC), both designed for room temperature operation. In particular, the frequency dispersion of the dielectric properties and tunability of PE Ba_xSr_(1-x)TiO_3- and BaZr_yTi_(1-y)O_3-thick films have been extracted from broadband measurements of CoPlanar Waveguides (CPW) structures over a wide frequency range up to 26.5 GHz, using an introduced enhanced quasi-TEM CPW model. A substantial progress is reported in the design, characterization and application of novel LC mixtures for microwaves, leading to a tunable phase-shifter figure-of-merit of 110°/dB at 24 GHz, that is the highest value ever reported for tunable microwave dielectrics above 10 GHz at room temperature. This opens up totally new low-cost LC applications beyond optics, particularly in the millimeter wave range.