Interactive transmission line computer program for undergraduate teaching

Distributed-circuit analysis using transmission lines is a standard topic in undergraduate education in electrical engineering and computer engineering. This paper presents a simple menu-driven program that students can use to explore the behavior of transmission line circuits, and as a computational laboratory for verifying their solutions to homework problems. At the introductory level the program demonstrates traveling waves and standing waves. Smith-chart calculations of impedance and reflection coefficient can be associated with the standing-wave pattern on the transmission line. A branching circuit can be solved, including impedance matching with a quarter-wave transformer. At the intermediate level, students can use the program to test their designs for two- and three-step Chebyshev transformers, and for impedance matching using single, double and triple-stub circuits. The program makes easy the calculation of the bandwidth of a design by displaying the return loss or transmission loss as a function of frequency. Low-pass and bandstop filters can be solved. The program encourages students to explore the behavior of the voltages and currents on the lines as the frequency is changed to gain insight into the operation of transformers, matching schemes and filters.