At low frequencies, the classic transmission line (TL) equation can be used to calculate the voltage and current of the line and its loads. Because of the application of the quasi-TEM mode approximation, the classic TL equation is not available for the TL problem at higher frequencies. Based on Maxwell's equations and electromagnetic scattering theory, the high-frequency TL equation is established. This equation has a similar structure to the classic TL equation and contains new distributed parameters (high-frequency TL distributed parameters), but the parameters are distinct with the classic TL counterparts. The two kinds of distributed parameters are approximately same at low frequency, but there will be larger and larger differences between them when the frequency increases. According to some analysis and simulation examples, it can be shown that the same calculated results can be obtained by applying high-frequency TL distributed parameters and the full-wave analysis method. By using high-frequency TL and its distributed parameters, we have another way to analysis high-frequency TL problems in case that the classical TL theory is not available.
