E. Versluys, A. Long
Keywords: RF, antenna, GRIN, lens, additive manufacturing, DLP, manufacturing, electromagnetics, EW, C5ISR, 5G, mmWave, telecom
Summary:Gradient Index (GRIN) devices have been explored for their potential benefits in enabling performance from simple radiating elements that could theoretically exceed that which is typically found in high-end beamforming or digital arrays. However, the technology to design and manufacture GRIN lenses has typically been difficult, time consuming, and/or expensive, so the primary work has occurred in academia and labs, and has not been widely available to commercial or military users. Fortify has been pioneering the scalable manufacturing of GRIN devices with its family of low-loss photopolymer dielectric resins. When combined with Fortify’s Flux Core DLP additive manufacturing system, high resolution and fine features can be produced in materials that have stable dielectrics and loss tangents more than an order of magnitude less than existing photopolymer materials on the market. These fine features enable higher frequency Millimeter Wave (MMW) devices that can be produced in a robust manufacturing process, and the non-metallic GRIN architectures ensure extremely high instantaneous bandwidth and low dispersion in the lens. As GRIN devices become an economically viable option for telecom and defense RF systems, new architectures are being developed that enable high performance with low-cost, simple RF radiators. In collaboration with the Southwest Research Institute, Fortify has created a multi-beam aperture that uses a unique combination of Gutman and Eaton type GRIN lenses to create an aperture with full hemispherical coverage that operates from 3.5 GHz to 18 GHz bandwidth. We describe the material characteristics, the design process for the aperture and lens, methods used to reduce impedance mismatch in the RF chain, and the manufacturing, assembly, and testing of the aperture. In order to create the aperture of this size, 9 separate sections were printed on the Flux Core machine and assembled together to create one effective lens, with corresponding testing done to ensure the sectioning would not have adverse effects on the RF performance. The aperture was tested with multiple distinct RF beams, and peak gain at different azimuth and elevation, with sidelobe characterization, was measured. The practical test results were characterized against simulated results. We also describe the RF-specific digital thread tool set provided by Fortify, which enables RF designers to connect directly from their existing computational electromagnetics solvers, through the creation of effective permittivity in 3-dimensional space, to realizing the final physical part in a user-friendly digital interface. With the combination of the advanced toolset, a robust scalable manufacturing process, and additional research into unique gradient index profiles, RF designers now have a new capability to enhance gain, field of view, or efficiency specific to their designs in defense, 5G/6G, mmWave, and automotive applications.