SPICE Simulation of Transmission Lines by the Telegrapher's Method (Part 3 of 3)

Users of SPICE have used two methods to simulate transmission lines: 1) use one of SPICE's built in transmission line models or 2) use a series of lumped-component sub-circuit approximations. Neither method has been completely satisfactory, and neither method directly addresses the fact that some of the line parameters are functions of frequency.

There is a better way, one which requires only about two-dozen components, regardless of the length or bandwidth of the transmission line. We will call it the Telegrapher's Method and the sub-circuit we create to implement it will be called the Telegrapher's Model or TM. By the end of this article, we will have a SPICE sub-circuit that will implement the Telegrapher’s method with full frequency dependence and will be as easy to use as the built-in components.

This article is presented in three parts, as pdf files (no registration required), as follows (note that due to the tables and figures, it is in "landscape" layout format, and not the more-usual "portrait" layout):

• Part 1: Putting the Telegrapher's Equations into a Circuit
• Part 2: Putting Frequency Dependence into the Simulation
• Part 3: Putting the Telegrapher's Equations into a Usable Sub-Circuit

About the author
Roy McCammon is a senior engineer with 3M's Communication Markets Division, and a graduate of the University of Texas Department of Electrical Engineering. He has operated a satellite tracking station in Antarctica, designed astronomical instruments and telescope servos, and has spent the last 28 years designing test equipment used by telecommunications providers and thinking about transmission lines. His interests include dancing the two-step, pushing miniature battleships around a table top, and simulations.