Surface Roughness Modeling of Substrate Integrated Waveguide in D-Band

In this paper, surface roughness models for a substrate integrated waveguide (SIW) are proposed. Frequency-dependent conductivity is introduced to model the conductor loss due to surface roughness. To be specific, two models, namely, the modified Huray model and the rigorous waveguide model, are developed. Both models take into account the mode-dependent loss. Formulations for enhancement factor are derived for both models to calculate the frequency-dependent conductivity. Key parameters of the analytical models are extracted from the surface profile measurement. A D-band (110-170 GHz) SIW structure is fabricated using a liquid crystal polymer substrate. The simulated results are correlated with measured data of the fabricated SIW, which shows the accuracy of the proposed methods.