Electro Chromic-Based Unit Cell for Millimeter-Wave Reconfigurable Reflectarrays

In this paper, the feasibility of exploiting the dielectric tunability of a novel tuneable material, namely Electro Chromic (EC) material, to construct a reflectarray unit cell is demonstrated for the first time. In this regard, the design of an EC-based reflectarray unit cell which provides electronic control of the reflection phase at millimeter wave frequencies is presented. The unit cell is an aperture-coupled microstrip patch which exhibits a maximum reflection phase shift of about Δϕ = 133° at the center frequency of fc = 299.7 GHz.

I. Introduction

A great deal of attention has recently been focused on developing bulk electronically tunable materials due to their potential applications in various integrated reconfigurable microwave and millimeter wave devices and antennas. For example, the ability to change the relative permittivity of a material by applying a bias voltage provides a means for creating compact, low cost and integrated phase shifters for manufacturing high gain electronic beam steering antennas, [1]. For this purpose, the two main options available to designers, nematic liquid crystals (LCs) and ferroelectrics (FEs), have been extensively investigated and reported in the literature. Although these materials exhibit dielectric tunability, several limitations have been identified, such as low levels of dielectric tunability (LCs) and high values of dielectric permittivities (FEs), restricting their use as true bulk tuneable materials. A new class of bulk-tuneable materials, based on inorganic Electro-Chromic (EC) materials was recently demonstrated as an alternative solution for use at RF/mm-wave frequencies [2], [3], [4].