Advanced Hybrid Gradient Index Lenses via Additive Manufacturing of Low-Loss Materials

Radio frequency (RF) systems are a key enabler of multi-domain mesh networked capabilities in the battlefield of the 21st century. As attritable and expendable unmanned platforms become more common, cost is becoming a larger constraining factor in system specifications. Current high-performance RF systems such as phased arrays meet mission requirements but are costly and consume significant power. Gradient Index Lens Switchable Beam Arrays are a solution that is passive, low cost, extremely high bandwidth, and can handle high power. However, GRIN lenses have current limitations in size, cost, and manufacturability. High Dk material and broad permittivity range is necessary for volume, mass, and cost reduction of GRIN lenses since cost is proportional to print time and hence volume. Transformation optics techniques can be used to reduce the required size of lenses, but the methods require both high DkÆs and broad permittivity ranges to achieve reasonable compression ratios. Materials are available with these high Dk values, however, assembling bulk dielectrics to achieve greater ranges introduces step changes in permittivity, which reduce aperture efficiency and increase sidelobes. A smooth gradient is required across the total dielectric range, which is achievable with additive manufacturing (AM) and tuned lattice structures. AM enables design freedom for gradient indices with tuned lattices mixing air and dielectric to achieve effective permittivities, but current materials and systems require a tradeoff between low RF loss or high frequency performance. Fortify has developed a line of low-loss RF photopolymer composites for the DLP Flux system that enables RF components to be built with stable dielectrics, fine features, and the lowest loss on the market. By combining these materials in different areas of a GRIN lens, broad Dk ranges can be achieved to implement compression ratios > 5, with smooth gradients that provide low scan loss coefficients and minimize sidelobes. The fundamental goal of this Phase I effort is to demonstrate the feasibility of combining discrete 3D-printed dielectric materials within a single lens to extend the permittivity range beyond what is possible with a single material, with index matching at the interfaces to produce smooth dielectric gradients throughout the entire structure. The lenses produced with this technique promise extremely large instantaneous bandwidth, conformal integration into air vehicles or other platforms, the potential for high power handling, and above all, low cost and rapid manufacturing. They support the implementation of a simple, high performance, reliable RF system to meet the needs of low-cost platforms across domains in the DoD.