What is Wave Impedance in Electromagnetics

Wave impedance is the ratio of the electric field strength to the magnetic field strength in an electromagnetic wave. It is an important parameter in RF engineering, antenna design, wave propagation analysis and transmission systems, influencing energy transfer, reflection characteristics and electromagnetic field behavior.

As we know, when an electromagnetic wave propagates through a medium, a changing magnetic field (H) generates an electric field (E) and conversely. The propagation of these waves is driven by these two oscillating H and E fields. The area closest to the source of radiation experiences a higher intensity of these fields.

Definition of Wave Impedance

Wave impedance is defined as the ratio of the electric field (E) to the magnetic field (H). Mathematically:

Wave impedance = |E| / |H|

Wave Impedance and Field Dominance

• High Wave Impedance: Wave impedance is high in regions where the electric field (E) is dominant. For example, this occurs with a straight wire fed by a high-impedance, voltage-driven source.
• Low Wave Impedance: Wave impedance is low in regions where the magnetic field (H) is dominant. This is observed in scenarios like a loop or coil fed by a low-impedance, current-driven source.