Near and far field
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In the study of diffraction and antenna design, the near field is that part of the radiated field that is within a small number of wavelengths of the diffracting edge or antenna. The part of the radiated field that is beyond this is known as the far field.
In telecommunication, the term near-field region has the following meanings:
1. The close-in region of an antenna wherein the angular field distribution is dependent upon distance from the antenna. Synonyms near field, near zone.
2. In the study of diffraction and antenna design, the near field is that part of the radiated field that is within a small number of wavelengths of the diffracting edge or antenna.
3. In optical fiber communications, the region close to a source or aperture.
Note: The diffraction pattern in this region typically differs significantly from that observed at infinity and varies with distance from the source.
- Source: from Federal Standard 1037C and from MIL-STD-188
In telecommunication, far-field region is the region outside the near-field region where the angular field distribution is essentially independent of distance from the source.
1. If the source has a maximum overall dimension D that is large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than 2D 2/λ from the source, λ being the wavelength.
2. For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Synonyms far field, far zone, Fraunhofer region, radiation field.
- Source: from Federal Standard 1037C and from MIL-STD-188
See also
- Fresnel diffraction (for the near field)
- Fraunhofer diffraction (for the far field)
- Near_Field_Communication (Near Field Communication Technology)