A Comprehensive Review of Surface Roughness Effects on Microwave Performance of Transmission Lines

Over the past few decades, microwave electronics have been advancing toward higher levels of miniaturization and integration, accompanied by a continual increase in operating frequencies. In the early stages of low-frequency electronics, the skin effect was relatively negligible. However, with increasing frequencies, it has become a critical factor affecting the microwave performance of electronic devices. Moreover, as device dimensions shrink, the skin depth becomes comparable to the surface roughness of conductive components, further intensifying these effects. As critical carriers of signal transmission in electronic devices, transmission lines now face growing challenges from surface roughness at microwave frequencies. In this work, we review the impact of surface roughness on the microwave performance of transmission lines, investigate the underlying physical mechanisms, and address conflicting findings in existing literature. We also compare three categories of surface roughness models—topological, phenomenological, and fractal—emphasizing the role of correlation factors in phenomenological models and discussing the strengths and limitations of each approach. We also summarize the primary mathematical methods used to analyze the microwave performance of transmission lines. Furthermore, we explore how surface roughness affects transmission line characteristics, including effective permittivity, characteristic impedance, attenuation, phase delay, and loss. Finally, we propose several strategies for mitigating the adverse effects of surface roughness on microwave transmission line performance.