Transmission Lines and Reflected Signals

Transmission lines are a very important circuit element in electrical engineering. Transmission lines are distributed elements, in contrast to lumped elements such as resistors (R), capacitors (C), and inductors (L). The electrical characteristics of a distributed element depend upon its physical geometry, and the electromagnetic fields which dictate its circuit behavior are distributed over a range of space. Unlike in a purely lumped element circuit, geometry matters and is a primary factor for how the circuit behaves. A transmission line cannot be described by a simple current-voltage (I-V) relationship like RCL elements can. Distributed elements, such as transmission lines, are more fundamentally described by the electromagnetic field distributions, which can be either static (DC), time harmonic (AC), or transient waves or pulses. Transmission lines, the subject of this laboratory, are conduits for the propagation of electromagnetic waves which carry both information and power. Travelling waves interact with inhomogeneities in their path, and these produce reflections. These reflected waves are an integral aspect of transmission line behavior which can be both useful and a challenge to manage.