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 Dks 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.
Benefit: As mentioned in our letters of support from key defense and commercial customers, cost and performance go hand-in-hand as they are developing new systems for future capabilities. Current beamforming systems include phased arrays and holographic beamformers, which are both expensive, especially when high bandwidth is required. Phased arrays are also electronically steered through phase shifting at the element level, which requires significant operational power and may introduce cooling requirements and other system costs. The ability to simplify RF system architectures, reduce components, and unitize functionality in RF systems will enable significant cost reductions without sacrificing performance while improving reliability and environmental survivability. In the DoD context, this will enable higher-performance RF systems to be integrated into thousands of unmanned systems in the air, space, surface, and at sea to perform missions from ISR, EW, communication nodes, and multi-domain networking. Naval surface vehicles jamming large areas of the battle space with beams of high power RF energy, to small, unmanned platforms acting as decoys for other manned aircraft while also performing as sensor nodes in a mesh network, to hypersonic missiles with unitized structures and sensors are examples of areas where this concept can have effect on cost and performance. In the commercial context, the telecommunications market is large ($20B), rapidly growing (16% CAGR) and is recession proof. Increasing network speed and capacity while reducing infrastructure cost has a direct impact on the bottom lines for all network providers. Current base stations use phased array or holographic beamforming systems and are limited to fields of view of about 120, requiring multiple systems per tower location. By increasing the field of view with GRIN lenses, larger areas can be covered by less antennas, directly reducing the cost of the infrastructure. Additionally, the satellite broadband market is rapidly expanding, with Starlink, OneWeb, Amazon Kuiper, and other suppliers all vying for market share. These suppliers are suspected to be selling base stations at a loss, so the cost of these components is a critical factor in the profitability of the network. GRIN lens arrays offer a lower cost solution than phased array systems without sacrificing performance. With key partnerships established with innovators at the forefront of microwave GRIN research, and across the RF component value stream, Fortify is well positioned to develop this key technology through this Phase I and follow on Phase II work, and to scale quickly for commercial and defense implementation.
Keywords: GRIN, GRIN, EW, RF, C5ISR, UAS, additive manufacturing, Antenna, phased array
