Additive Manufacturing of a Luneburg Lens for Electromagnetic Applications

We present the design, fabrication, and experimental characterization of two 150 mm Luneburg lenses for X-band (10 GHz), produced by FFF using standard PLA. The printed PLA permittivity was measured with a 7 mm coaxial cell and EpsiMu, yielding εr, PLA ≈ 2.5 at 100% infill; a volume-weighted mixing model with perimeter correction was used to set discrete radial infill fractions. Two infill patterns (grid and gyroid) were tested, and waveguide mounts were integrated for reproducible alignment. Insertion-loss tests give 1.5 dB (grid) and 1.1 dB (gyroid) at 10 GHz. Far-field measurements (R = 1.5 m) and Friis-based estimates yield peak gains of 20.5 dBi (grid) and 19.4 dBi (gyroid) (simulation: 20.8 dBi); the waveguide reference gain is 4.9 dBi. Near-field tests at R = 0.15 m show an on-axis S21 improvement of +2.33 dB, which corresponds to a low apparent near-field aperture efficiency (1.8-2.3%) while far-field efficiencies inferred from the measured gains are substantially higher (35-45%). These results confirm that discrete infill grading in low-cost FFF-printed PLA can realize effective Luneburg lenses at X-band, with quantifiable trade-offs among insertion loss, infill geometry, and realized aperture efficiency.