Tunable reflectarray unit cell element using BST technology

A tunable reflectarray unit cell is presented in this paper using Barium Strontium Titanate (BST) technology. A square patch is capacitively loaded with a narrow gap in the middle and a BST thin-film layer is deposited under the patch. The BST layer is etched away everywhere except for the area under the gap for minimum loss. By tuning the DC bias voltage across the gap, the dielectric constant of the BST layer changes, which results in a change in the effective capacitance of the gap. Therefore, the reflection phase of the reflectarray unit cell can be continuously controlled. Simulation and measurement results are presented at 12.3 GHz. Due to the monolithic integration of the tuning mechanism with the unit cell, this configuration can be applied at millimeter-wave frequencies without suffering from packaging and bonding problems.