Recent progress in electronically tunable reflectarray technology using liquid crystals

In this paper we present an overview of liquid crystal based reflectarray technology which has been developed over the past five years at Queen´s University Belfast, Universidad Politecnica de Madrid and Universidad de Oviedo. This new active control strategy requires precise characterisation of the permittivity, dielectric anisotropy and loss tangent of the liquid crystals. The electrical parameters are obtained by fitting computed results to reflection phase and amplitude plots of reflectarray elements measured in the 9.4 -10.4 GHz and 115 - 150 GHz bands and transmission coefficients of a frequency selective surface in the range 300 - 320 GHz. The validity of this new active control strategy is demonstrated by designing a reflectarray antenna which exploits the dielectric anisotropic property of liquid crystals to generate a beam that can be electronically switched from a sum to a difference radiation pattern. The simulated results are shown to be in good agreement with measurements performed at X-band. The paper concludes by showing that the narrow scan profile of an Earth observation limbsounder instrument can be obtained using a dual reflector antenna with a liquid crystal backed reflectarray subreflector. Experimental verification of the numerical results are presented at 94 GHz using a 784 element printed patch reflectarray subreflector which was designed to tilt the beam 5° from the boresight direction.