Additive Manufacturing of Graded Dielectric Superstrate for Phased Arrays

Additive manufacturing technologies have enabled a wide range of custom devices and advanced material fabrication. It is reported here an approach developed to provide dielectric graded RF metamaterials through an active mixing nozzle developed in prior work and novel low loss inks. By utilizing a active mixing nozzle, we can provide a continuous gradient across the z-stack of a material from a permittivity of 3 to 1.06 with the inclusion of a top layer of Rohacell. Utilizing this superstrate material surpasses traditional approaches in manufacturing graded index materials which require gluing substrates with various dielectric constants together or machining varying holes across a substrate or space filling 3D printed parts. In this study we developed a non-destructive characterization approach through micro-CT. By utilizing our approach to fabricate a superstrate we can improve the scan angle and bandwidth of traditional phased arrays

I. Introduction

The microwave industry is showing greater interest in Graded index (GRIN) materials to fabricate flat lenses, thinner superstrates, etc. Often, these GRIN materials are composed of either space-filled or laminated dielectric layers. Space filling can be costly due to the number of holes required to represent lower permittivity dielectrics as well as this technology creates inherent frequency dependence in the material. Laminated dielectrics have the downside of needing a lamination layer that causes a discontinuity in what should otherwise be a smooth taper. This paper presents the use of a direct-write solvent-based 3D printing method to create a smooth taper for use with a GRIN superstrate. The direct-write method utilizes SIS loaded with a varying amount of SrTiO3 to allow for a continuous transition between a dielectric constant of 2 to 26. The SIS material is loaded with 3M K1 glass in order to increase the structural rigidity and hopefully decrease the dielectric constant and denoted HGS for hollow glass sphere.