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

Shiyu Zhang,Ravi Kumar Arya,J C Vardaxoglou,William G Whittow,Darren Cadman,Raj Mittra

doi:10.1109/tap.2020.3044586

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.

Highlights

C ONVEX lenses are well-known optical devices that converge impinging parallel rays to a spot at the focal point
The partial in-filled structure had been proven earlier to have an effective permittivity and behave as though it were comprised of a homogenous dielectric material, it was simulated under periodic boundary conditions
All three lenses had similar half-power beamwidths (HPBWs) levels in the E-plane, which started at ∼11◦ at 12 GHz and reduced to ∼3.6◦ as the frequency was increased to 40 GHz

Summary

Introduction

C ONVEX lenses are well-known optical devices that converge impinging parallel rays to a spot at the focal point. Engineering and Physical Sciences Research Council (EPSRC) Doctoral Prize Research Fellowship and in part by EPSRC Grand Challenge “Synthesizing 3D Metamaterials for RF, Microwave, and THz Applications” (SYMETA) under Grant EP/N010493/1. (Corresponding author: Shiyu Zhang.)

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