Design and Evaluation of Liquid Crystal-Based Pixels for Millimeter and Sub-Millimeter Electrically Addressable Spatial Wave Modulators

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Abstract
During the last decades, the Liquid Crystal (LC) technology has been widely used in the near infrared and visible regions of spectrum to develop tunable devices such as displays or spatial light modulators (SLM), which is the term used in photonic to describe an aperture antenna fed by an external source in reflection or transmission mode, known as reflectarray (RA) and transmitarray (TA) in microwaves. However, the use of the LC to implement tunable devices for millimeter and sub-millimeter waves is very recent. In the particular case of RAs/TAs, some efforts have been made in the last recent years to develop LC-pixels [1]–[3] or full antennas [2]–[3] up to 100 GHz. The main difference between both an LC-pixel in these frequencies and that one developed to operate in photonic applications lies in the use of resonators, which must be included in the pixels (cells) to achieve the appropriate phase-shift (Fig 1). The use of resonators makes the performance of the cells completely different for the critical electrical parameters, which also depends on the particular characteristics of the LC mixture used (dielectric anisotropy and loss tangent) at the operating frequency.