Improvement of Phase-Shifting Properties in Coplanar Waveguide-Type Liquid Crystal Millimeter-Wave Phase Shifter by Introducing a Resonant Phenomenon

Abstract

Nematic liquid crystal (LC) material is mounted on a coplanar waveguide (CPW) substrate, which is well known as an excellent transmission line for superhigh-frequency electromagnetic waves, to achieve an electronically tunable phase shifter. In our previous work, an upper electrode introduced for an LC drive significantly contributed to reducing the driving voltage with large phase-shifting properties. However, it also tended to increase transmission loss. Thus, it was clarified that it is not necessarily a desirable improvement if we evaluate the device performance by balancing the phase shift and loss. In this work, we propose a triangular pattern for the upper electrode to utilize a resonant phenomenon and to improve the phase-shifting properties. A periodic dip appears in the transmission spectra and some fluctuations appear in the phase properties near the dip frequency. It is found that the phase shift becomes very large at frequencies slightly lower than the dip frequency, although the frequency band in which the large phase shifts occur is limited.