28-GHz Foldable Reflectarray
Many conventional designs employ other configurations to enhance the efficiency of a reflectarray by achieving a wider bandwidth or dual-polarization which improves the robustness of the reflected signals. Some examples are multi-layered reflectarrays that achieve a wider bandwidth at the expense of being thicker and complex to fabricate, and multi-resonant designs that can operate at multi-frequencies but require complex geometries that have smaller fabrication tolerances. More recently, reflectarrays incorporate an RIS design that utilizes elements that can be configured electrically, such as PIN diodes, varactor diodes, or liquid crystal substrates. The Liquid-Metal Electronics VIP team at the University of Hawaii at Manoa, for example, have demonstrated reconfigurable reflectarrays consisting of liquid metal elements actuated by voltage. However, this required a complex and lengthy fabrication process.
Given these challenges, a foldable reflectarray with a simple design is highly desirable. This combines portability and limited reconfigurability, enabling adjustments in the directivity and reflected power of signals without significant fabrication or design complexity, and eliminating the need for electrical power.
The methodology includes the design, simulation, fabrication, and testing of a foldable 28-GHz reflectarray antenna. The approach was divided into three main stages: unit cell design, reflectarray design, and fabrication and testing. First, a unit cell was designed and simulated using Ansys HFSS software to determine the reflection phase and magnitude at the frequency of 28 GHz. These results were then used to configure the overall reflectarray phase gradient to establish the highest possible phase state in a column-by-column phase shift. Finally, the fabricated arrays were measured to validate the accuracy of the simulation and assess the impact of aperture size and folding geometry on reflected power and directivity.
More information will be provided in the report.