Reflective liquid crystal terahertz phase shifter with tuning range of over 360°

Abstract

This study presents the design and experiment of a terahertz reflective phase shifter based on liquid crystal. The proposed voltage-tunable phase shifter takes advantage of the variable permittivity of the liquid crystal, adjusted by an external electric field, providing tunable reflective phase shift of terahertz (THz) waves. We analysed the performance of this phase shifter using a simple isotropic and homogeneous model considering the angle of incidence. The phase variation was achieved in a range greater than 360° and frequencies from 349 to 361 GHz. An array constituted of 900 patch elements was fabricated using the photolithographic process. It provided tunable phase range of 350° over the frequency range of 353.5–359.3 GHz at 40 V, where a maximum phase shift 362.6° was achieved at 357 GHz. The LC dielectric constant was obtained by fitting the computed reflectance spectrum to the measured result. We compared accurate model, considering both inhomogeneity and anisotropy of the liquid crystal, with the simplified model. In addition, the differences were analysed between the measurements, accurate and conventional model. The results show the liquid crystal phase shifter is great for beam scanning antenna array in THz.