Ultra-Wideband Flat Metamaterial GRIN Lenses Assisted With Additive Manufacturing Technique

TLDR

The study designs ultrawideband flat GRIN lenses covering 12–40 GHz with over 108 % fractional bandwidth. The lenses are engineered using a frequency‑independent ray‑optics method to compute a radially varying permittivity profile, realized via two additive‑manufacturing techniques—partially infilled dielectrics with variable periodicity and subwavelength‑scale metallic‑inclusion engineered dielectrics—to achieve the required permittivity distribution. Measurements confirm that the lenses boost open‑ended waveguide source gain by 8.7–15.6 dB (up to 23.6 dBi) across 12–40 GHz, validating their suitability for high‑directivity, beamforming antennas over an ultrawideband.

Abstract

This article presents the designs of ultrawideband microwave flat gradient index (GRIN) lenses, which realizes over a 108% fractional bandwidth (12-40 GHz). The frequency-independent ray optics method is employed to determine the radially varying permittivity profile of the lenses. The challenge of realizing such a radially varying profile and the limitations in dielectric material choices are overcome by two additive-manufacturing-aided approaches: 1) partially infilled dielectrics with a varied periodicity, which ensures the lens performance at the higher end of the frequency range and 2) artificially engineered dielectrics (AED) with subwavelength-scale metallic inclusions, which enables-high permittivity dielectrics and leads to benefits of thickness and mass reduction for the GRIN lenses. Measured results demonstrate that the GRIN lenses improve the gain of open-ended waveguide sources by 8.7-15.6 dB over a wide frequency range from 12 to 40 GHz, with the realized gain of up to 23.6 dBi. Both the simulation and measurements of the presented design confirm the potential of implementing the proposed GRIN lens design in high directivity and beamforming antenna applications, across an ultrawideband frequency range.