This openEMS comparison keeps the driven and pickup traces fixed and changes the reference plane: continuous copper versus a finite 2 mm × 20 mm slot. Ground remains connected around the ends of the slot.
Color represents complex sheet-current magnitude, estimated using Jₛ = ẑ × (H above − H below). The refined field samples are at z = ±0.125 mm. White arrows show the direction at a selected phase, with equal lengths. Metal is absent inside the slot, so that region has no sheet-current cells.
The viewer starts at 2 GHz in top view. Use 3D view to rotate, move the current-phase slider, or select electric field to inspect a slice just below ground. Both layouts and all five frequencies share a color scale for each quantity.
A field magnitude map in air need not show an empty shape matching the slot. The current map answers where the return flows; the below-ground electric field shows aperture leakage.
At 2 GHz, the refined slotted case has 20.50 dB higher S31 than the continuous-plane case. S31 describes coupling into the specified terminated pickup port. It is not a radiated-emissions measurement. The 2 GHz difference changes from 19.62 to 20.50 dB with refinement.
The plane is 60 × 40 mm. The driven trace is 40 × 2 mm, and the pickup is 30 × 2 mm at y = 8 mm. Both lie 1 mm above ground on a lossless εᵣ = 4.2 dielectric. Each trace end has a 50 Ω port. Conductors are zero-thickness PEC. The Gaussian test excitation provides frequency components; the displayed GHz values are not the switching frequency of a converter.
All four runs, two geometries at two mesh settings, reached the requested −60 dB residual-energy criterion. Local refinement uses 0.25 mm cells around the slot, trace widths and dielectric. One refinement checks sensitivity; it is not a universal error bound. The current estimate is sensitive to sampling near metal edges. Display interpolation and isosurfaces do not replace the raw solver fields.
Original teaching calculations prepared for Dodec Labs. Raw HDF5 fields and solver scripts remain in the source project archive.