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The accurate characterization of the effect of conductor surface roughness in microwave transmission lines is crucial in the analysis and design of microwave circuits, in particular at high frequencies. This paper proposes an accurate correction factor based method to calculate the effect of conductor surface roughness from the per‐unit‐length (P.U.L.) parameters and the complex propagation constant of a microstrip line. Then, this correction factor is applied to extract the dielectric properties of microstrip lines, thus taking into account the conductor surface roughness. The simulation results show a good agreement with the given standard values.

Abstract-"Curve-fitting" method is an important method to extract dielectric parameters of substrate materials from planar transmission lines. At gigahertz frequencies, effective conductivity concept is adopted to model the conductor's surface roughness effects in planar transmission lines, and differential extrapolation method is used to remove surface roughness effects. However, such a concept and method lose their accuracy at extremely high frequency such as terahertz waves. This paper details some new limitations in the terahertz regime and proposes corrections in calculating effective conductivity with rough conductor and curve-fitting method for transmission performance characterization in eliminating the effects of surface roughness. The proposed method is validated by simulation data for conductivity with parallel plate waveguide model, and the corrected method presented here can effectively extract dielectric parameters with an error less than 7%.

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