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

We describe a computational imaging technique to extend the depth-of-field of a 94-GHz imaging system. The technique uses a cubic phase element in the pupil plane of the system to render system operation relatively insensitive to object distance. However, the cubic phase element also introduces aberrations but, since these are fixed and known, we remove them using post-detection signal processing. We present experimental results that validate system performance and indicate a greater than four-fold increase in depth-of-field from 17" to greater than 68".Index Terms-Computational imaging, extended depth of field, millimeter wave imaging.

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A method for synthesizing broadband antireflective (AR) surfaces at millimeter wave frequencies is demonstrated. AR surfaces were formed by machining a multilayer subwavelength structures into nonabsorptive dielectrics. This created low‐reflected energies (<−25 dB) over large bandwidths and incidence angles. Experimental results are provided demonstrating the validity of the method. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 561–568, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24973

In this work we describe the use of laser direct-write for the rapid prototyping of frequency selective surfaces. Frequency selective surfaces are generally described by a periodic array of conducting or dielectric features (i.e. crosses, loops, grids, etc.) that when properly designed can pass or reject specific frequency bands of incoming electromagnetic radiation. While simple frequency selective surfaces are relatively straight forward to design and fabricate, operational demands, particularly military, have motivated the design and fabrication of much more complicated patterns. These new designs combine features of significantly different length scales, randomly dithered patterns and combinations of passive and active elements. We will demonstrate how laser direct-write is an ideal tool for the rapid prototyping of these new more complicated frequency selective surface designs. We will present experimental results for devices fabricated using several different laser direct-write processes.