Modeling and measurement of coplanar transmission lines with significant proximity and surface roughness effects

New technologies have resulted in transmission lines that deviate significantly from the intended rectangular cross-sections. Trapezoidal cross-sections and roughness that penetrates a significant depth into the surface in comparison to the thickness of the conductor can cause a very significant deviation in transmission line parameters from predicted values. Proximity effects further complicate the analysis by increasing losses and changing the impact of surface roughness by changing the current distribution. A skin-effect filament model is presented that accounts for surface roughness effects and non-ideal cross-sections in the presence of a strong proximity effect. The model is compared to a state-of-the-art full-wave approach and shows a better agreement to the measurement of a printed coplanar transmission line.