Lossy Two-Conductor Transmission Lines with Frequency-Dependent Parameters

This chapter deals with the problem of asymptotic behavior of the per-unit-length admittance and impedance of the line. The network functions describing a generic (uniform) two-conductor line as a two-port in the Laplace domain are: the line characteristic impedance and the line characteristic admittance. It recalls the general behavior of the admittance and impedance functions for transmission lines modeling guiding structures of interest in digital and communication networks. These lines have dielectric dispersive in time, frequency-dependent dielectric losses, and skin effect. This chapter also discusses transmission lines modeling power lines above a finite conductivity ground and superconducting guiding structures. However, the transmission line model can still be applied when the quasi-TEM hypothesis is no longer satisfied. In ideal guiding structures the behavior of each higher propagation mode can be described in terms of an equivalent transmission line, whose parameters are frequency dependent and can be obtained by solving Maxwell equations. In the most general case of open lossy interconnections with a nonhomogeneous dielectric, operating at high frequencies, an equivalent frequency dependent transmission-line model is found by using a full-wave approach.