A new method for synthesizing broadband antireflective (AR) surfaces at microwave and millimeter wave frequencies is demonstrated. The AR surface, we call an inverse motheye, was formed by machining a multi-layer grating of subwavelength circular holes into a non-absorptive dielectric. This created low reflected energies ( 30 dB) over reasonably large bandwidths and incidence angles. An optimization algorithm, based on a direct pattern search, integrated with a rigorous electromagnetic model was used to design the grating geometries. Experimental results are provided at Ka-band demonstrating the validity of the method.

In this paper the authors present a novel design tool for realizing dielectric structures with spatially varying electromagnetic properties via additive manufacturing (AM). To create tool paths ideal for AM processes, space-filling curves were utilized. Using fused deposition modeling (FDM), spatially varying structures were printed that produced a spatially varying relative permittivity. A wide range of varying fill fractions were printed and evaluated, demonstrating good agreement between the simulated and measured results. Furthermore, the authors verified that this design tool can be applied to practical structures by designing, printing and testing a gradient index flat lens.

A method for the fabrication of graded dielectrics within a structural composite is presented. This system employs an ultrasonic powder deposition head to print high dielectric powders onto a woven fabric composite substrate. It is shown how this system can integrate 3D variations of dielectric properties at millimeter resolution within a mechanically rugged substrate. To conclude, the system’s practical application is demonstrated with experimental results from a graded index lens.

We describe a new methodology for designing graded index lenses at microwave wavelengths with integrated antireflective properties. The method leads to a flat lens with minimal reflection losses at a frequency of interest. Both numerical and experimental results for two different design goals are shown to demonstrate the capabilities of the methodology. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2774–2781, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27198