Phase agile reflectarray cells based on liquid crystals

Experimental results at X-band are used to compare the electromagnetic scattering from a printed reflectarray cell, which is constructed on 500 mum thick layers of three different nematic state liquid crystals. It is shown that a small voltage can be used to vary the permittivity of the tunable substrate and thereby control the phase of the reflected signals. Numerical results using Ansoft HFSS are compared with the measured phase, resonant frequencies and signal attenuation for two orientations of the liquid crystal molecules. Data fitting is employed to quantify the loss tangent and the permittivity values of the three anisotropic specimens. The performance trade-offs that are imposed by the use of commercially available materials are discussed, and the computer model is used to specify the electrical properties of a liquid crystal mixture, which can provide a signal loss of < 1 dB and a dynamic phase range of 300deg from the patch elements at 10 GHz.