Low Order Transmission Line Modeling by Modal Decomposition and Minimum Phase Shift Fitting

Frequency dependent transmission line models of the traveling wave type are usually implemented via rational approximation of the characteristic admittance and the propagation function. For the propagation function, a delay needs first to be compensated before proceeding with the rational approximation. It has been shown that assumption of a lossless time delay can lead to significant loss of accuracy of the rational approximation itself. In this paper is shown a procedure suitable for approximating the magnitude of the propagation function with a minimum phase shift rational function. This enables a more efficient search for the optimal delay that gives best accuracy for a given order of the rational approximation, since the function does not need to be refitted in the delay optimization loop