3D-Printed Antireflection Structures for Enhanced Transmission in the 30–50 GHz Range

Paper in proceeding, 2025

We present a scale-model investigation of a novel, two-layer antireflection (AR) metamaterial intended for future 211–373 GHz (ALMA Bands 6 & 7) vacuum windows and cryogenic IR filters. To verify the concept rapidly and cost-effectively, the design was down-scaled to the 30–50 GHz band and fabricated in polypropylene on a commercial 3-D printer. Analytical quarter-wave transformer theory set the target impedances. These were done with a square unit-cell that alternates circular posts and complementary holes to obtain the required effective permittivity. Full-wave Floquet-periodic simulations predict < –20 dB reflection across the bandwidth. Quasi-optical measurements of the printed AR structure confirm that wide-band impedance matching can be achieved with entirely additively-manufactured polymer layers, which opens up-scaling the same topology to large-aperture windows for millimetre- and sub-millimetre-wave instruments in radioastronomy.