What is the Difference Between Near Field and Far Field?

The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. The key difference between near field and far field lies in their distance from the antenna or scattering object and the characteristics of the electromagnetic field in these regions.

Near Field:

The near field is the region closest to the antenna or scattering object.
In this region, the electric and magnetic fields are displaced by 90 degrees from each other.
The near-field region possesses an inductive effect and is sometimes referred to as the inductive field.
The antenna radiation pattern and strength of the fields vary with the distance from the antenna in the near-field region.
The near field can be further divided into the reactive near-field region and the radiative near-field region.

Far Field:

The far field is the region farthest from the antenna or scattering object.
In this region, the electromagnetic fields are dominated by radiating fields.
The E and H-fields are orthogonal to each other and to the direction of propagation in the far-field region.
The far-field region is characterized by a spherical wavefront, and the field strength decreases as the distance from the source increases.

The transition between the near field and far field occurs in the radiative near-field region or the Fresnel region. The boundaries between these regions are approximate rules of thumb, as there are no precise cutoffs between them, and even when precise boundaries can be defined in some cases, experts may differ in their use of nomenclature to describe the regions.