Two-Scale Coating-Budget Framework for Broadband Sub-6 GHz Transmission Recovery Through Commercial FTO Low-Emissivity Glazing

Low-emissivity glazing reduces heat transfer, but its continuous fluorine-doped tin oxide (FTO) coating attenuates wireless signals. A two-scale coating-budget framework treats coating removal as a cost to minimize inside the patterned window and over the whole pane. A laboratory insulating-glass unit of commercial K-Glass was laser-patterned over a 50 mm × 50 mm window on both cavity-facing surfaces with hexagonal-ring and square-patch arrays. The coating was modeled as a lossy sheet (design sheet resistance 17 Ω/sq; measured 12.4 ± 0.2 Ω/sq). Full-wave simulation predicts an intrinsic 0.7–6 GHz passband with ≈1.5 dB mean insertion loss, reproduced by a fitted equivalent-circuit model to 0.37 dB. Angular modeling keeps the passband to 40° for both polarizations (transverse-electric loss up to ≈3.5 dB); oblique incidence was not measured. Single-mounting free-space measurements show ≈15 dB mean transmission recovery over 1–6 GHz relative to the unpatterned unit; an independent campaign gives ≈19 dB at 2.4 GHz. Inside the patterned window, 47% of the coating is removed, yet 98.3% of the front-pane and 99.1% of the rear-pane coating remain on the 300 mm × 300 mm panes (98.7% combined). Area-averaged estimates bound the per-pane visible-transmittance change to 1.7 percentage points and emissivity rise to 0.012; neither was measured.