# Additive Manufacturing of Variable Density Lenses for Radio Frequency Communications in X-Band
## 1 Introduction
VPP, which uses ultraviolet light to selectively cure photopolymer resins, is valued for its high resolution and is often used to fabricate intricate components such as waveguides and lenses. In contrast, PBF enables the use of materials like polyamide polymer, which is lightweight and offers good mechanical stability and electrical transparency. As detailed by [14], using PBF to create support structures in RF devices enables engineers to maintain both structural integrity and desired electromagnetic transparency. The integration of these AM techniques has driven substantial advancements in the manufacture of complex antenna and lens structures, especially when complemented with material innovations like electroless metallization [15; 16; 17]. This article outlines the research gap that existed between integration of different additive manufacturing techniques (VPP, PBF), electroless metallization, and used materials (resin or nylon polymer) in developing radio frequency (RF) communication devices (previous measurements of EM properties of the material samples are accomplished in Section 2.2.4. Specifically, it focuses on the development of a horn antenna and a Gradient Index (GRIN) lens set, designed for operation in the X-band frequency range, making use of the capabilities of AM of polymeric materials. The work begins with measuring the dielectric permittivity and loss tangent of different polymeric materials at frequencies of 2.45 (WiFi at 2.4 GHz, 3G/4G mobile bands), 6.25 (WiFi at 5 GHz, 5G mobile bands, satellite communications), and 24.5 GHz (6G mobile bands, satellite communications). Furthermore, samples of stochastic and gyroid mesh structures of the different materials were measured, and the empirical relationships between material density and electromagnetic properties were established. Then, the lens set was designed. The design of the horn antenna, lens, and support structure was tailored to their specific functional requirements, both electromagnetic and mechanical. Three realizations of the GRIN lens were produced, using the results of the characterization of polymers whose dielectric properties vary with density, allowing for a radial permittivity gradient that enhances its focusing capabilities. The sets were then manufactured. The horn antenna, designed to be conductive, was fabricated using VPP with an acrylic resin with silica load and subsequently metallized using an electroless plating process. This combination ensures that the antenna meets the necessary conductivity specifications while benefiting from the lightweight and cost-effective nature of the polymer base. The support structure was fabricated using PBF with polyamide polymer, chosen for its mechanical stability and electrical transparency. This allows the support to maintain the structural integrity of the device without interfering with the antenna's radiation pattern. Finally, the three GRIN lenses were manufactured using different acrylic resins and meshes with different densities radially distributed. The final assembled devices were then evaluated for frequency response and radiation pattern, yielding results that aligned well with theoretical predictions and those of comparable studies in the existing literature.