Magnetic Field (H-Field)

Antenna Tutorial (Home)

Electromagnetic waves are made up of Electric Fields (often called the E-field) and Magnetic fields (also known as H-fields). What is an H-field?

The H-field is a vector quantity (has a magnitude and direction) and is measured in Amps/Meter [A/m]. Recall that the E-field points away from a positive point charge. An H-field curls (or wraps) around a wire of moving charge, as shown in Figure 1. Hence, H-fields are associated with moving electric charges.

magnetic field surrounding a wire carrying electric current

Figure 1. H-field associated with a static current.

There are no isolated magnetic charges as of 2008, so an H-field can't be defined as a force per unit magnetic charge in the way an E-field can be defined. However, magnetic dipoles do exist (magnets) which have a positive and negative end (or North and South). The magnetic field lines travel away from the North side and terminate on the south side.

field lines for magnetic dipole

Figure 2. H-field lines associated with magnetic dipole.

The H-field is orthogonal to the direction of propagation in a plane wave, as well as perpendicular to the E-field. It is the interaction of the E-field with the H-field in space that allows for wave propagation.

Custom Search
Definitions List

Antenna Theory (Home)