Filter Basics Part 6: Waveguides And Transmission Lines

In Part 5, we covered the basics of distributed element filter construction and gave an overview of two important methods for propagating electromagnetic waves around a circuit – waveguides and transmission lines. At a high level, the main difference between these two methods is the number of conductors involved and the types of electromagnetic modes supported. Let’s explore how each of these three types of electromagnetic modes work and how they are supported, or not supported, by waveguides and transmission lines.

Three Types of Electromagnetic Modes

When we say “modes”, what we are referencing is the different solutions to the electromagnetic field equations for the particular structure we are referring to. These three modes include transverse magnetic (TM), transverse electric (TE), and transverse electro-magnetic (TEM).

A TM mode solution involves the electric (E) field having components in the z-direction, which is along the direction of propagation, so that the magnetic (H) field is transverse, or at right angles to the z-direction (Figure 1).