Phenolic Foam Characterization for Millimeter Wave Luneburg Lens Antenna

This paper discusses the characterization of phenolic foam for plate Luneburg lens application. A Luneburg lens is achieved when the permittivity of the material is high at the center of the lens and gradually lowers towards the end of the lens following the Luneburg law. By utilizing a foam material, different values of permittivity of the same material can be achieved by expelling certain amount of air from the foam. There are several improvements that result from the introduction of phenolic foam to develop Luneburg lenses, including affordability, availability, and ease of fabrication. To achieve the desired permittivity, the foam undergoes a process of air expulsion using a hydraulic press machine. The material characterization involves three main steps: measuring the initial permittivity of the foam, expelling air using the hydraulic press, and finally permittivity measurement at different levels of air rejection. The permittivity of the foam is measured using dielectric assessment kit (DAK) and the results are tabulated and analyzed. The result shows that the higher the initial height of the foam, the more compact the foam would be after being pressed by the hydraulic machine to the final height. The permittivity value of the foam material is higher after the air particles inside of the foam are ejected. Looking into the future, this work will lead to speedy progress in beamforming and beam scanning application by offering a simpler solution to Luneburg lens.