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

In this Phase 2 proposal, Fortify proposes to develop a 3D printed steerable GRIN lens that has extreme bandwidth, low losses, and can be integrated into a naval or other DoD platform. The lens will be designed to have a conformal shape to match a prospective UAS external profile, with a 3-40 GHz operating bandwidth, a scan loss exponent of less than 2.5 from broadside to 50°, and peak sidelobes of lower than -20 at broadside and -15 at 50° scan. In the Phase 1 effort, Fortify and Notre Dame created a dielectric lens of 10” diameter, 2.1” thick, with a weight of 5.9 lbs manufactured and assembled from discrete, 3D printed lattice-based GRIN segments printed using polymer-composite and ceramic dielectric materials. The first lens achieved a measured radiation efficiency greater than 80% across the tested bands, broadside aperture efficiency greater than 57% up to 18 GHz, a sidelobe level 21dB below the main beam, and the scan loss exponent was 5.66. Fortify and Notre Dame observed that the lens efficiency is limited by two factors – the match bandwidth and the GRIN media. A key finding of the Phase 1 effort was that the prototype GRIN lens used a 6mm gyroid unit-cell and only operated well up to 19 GHz (in agreement with our maximum frequency theory). This result motivated the effort to reduce the gyroid unit-cell size for Phase 2, especially in the higher dielectric constant alumina ceramic material. The Phase 2 plan will use an iterative design approach, where over the base period ~four lenses of increasing capability will be designed, built, and tested. This effort will start by improving the scan loss and operating bandwidth, and finish with a conformal lens design integrated into a mechanical housing. The Phase 2 option period proposes to design, build, and test ~6 more lenses in which a radome and environmental sealing features will be added. Selected lens prototypes will be lab tested in environmental conditions relevant to end-use applications and may also undergo 10kW power testing if circumstances allow. Lens-to-lens variability is being evaluated in the Phase 1 option period and will continue in Phase 2 where lenses of the new designs will be built and tested for manufacturing variability.   The Phase 2 lens designs are supported by three additional tasks – Task 1 sets forth a plan to create a detailed set of system-requirements for integration of the lens into an end use application with integration consultants. Task 2 sets forth a plan to mature our lattice-based GRIN manufacture capability through focused development on materials and printing processes, targeting smaller unit cells and higher dielectric constants to increase the achievable effective dielectric constant range and upper frequency limits. Task 6 focuses on working with our strategic transition partners at LMCO and RTX to assess TRL and MRL levels, identify gaps, construct capability roadmaps, and conduct business case analyses.