This work is concerned with the improvement of a microwave liquid-crystal phase shifter using a large birefringence nematic liquid crystal. This material is a eutectic mixture of isothiocyanatotolane molecules. Microwave dielectric properties are reported and compared to the data obtained with the 5CB cyanobiphenyl material in the 26 -40 GHz frequency range using a rectangular waveguide. The phase-shifter design consists of a central cavity, where a liquid crystal is inserted, and two coplanar strip lines accesses. Its dimensions were calculated by electromagnetic simulation, using measured dielectric permittivities of the liquid crystal. The measurements were performed with a commercial Wiltron 3680 K probe test fixture. Phase-shift variations with and without bias voltage versus frequency are presented. As expected, the large-birefringence nematic liquid crystal exhibits a higher microwave dielectric anisotropy (Á" 0 ¼ 1:06 against 0.34) and the tunability of the phase shifter strongly increases (1.8 degÁcm À1 ÁGHz À1 against 0.8 degÁcm À1 ÁGHz À1 ).

A tunable, liquid-crystal (LC)-based, subwavelength Fabry-Perot (FP) resonator has been designed and fabricated in the 27-GHz band. The grid mirrors are identical and consist of metallic capacitive meshes characterized by a high filling ratio. This ensures simultaneously a high reflectivity and a strong negative phase of the reflection coefficient on the mirror so as to reduce the resonator thickness as much as possible. The resonator has been filled with a 110-m thick E3 nematic LC. A frequency shift of 6% has been obtained numerically (finite-difference timedomain (FDTD) simulations) using permittivity values measured under 1-T driving magnetic field ( = 2 91 = 2 52).An experimental tunability of 2% has been obtained by applying a 10-kHz ac bias voltage of 10 V. This lower value is due to the low driving field ( 0 1 V m), the nonperfect polyvinylalcohol (PVA) layer, and the relatively high thickness of the E3 mixture.Index Terms-Fabry-Perot (FP) resonator, liquid crystal (LC), subwavelength resonator.

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We report the electrical characterizations of La2Ti2O7 thin films synthetized by pulsed laser deposition. We observe a significant change in I–V curve in the presence of UV light. The conduction mechanism can be described by two regimes: ohmic at low voltage and space charge limited conduction for higher voltage. Finally, for the first time to our knowledge, the charge carrier mobility of this material is studied; we use the time-of-flight method to investigate this property. We explain the evolution of the carrier mobility with the applied voltage by the presence of a depletion layer between the film and the gold contact, which affects the measurements.