Near and far field
From Free net encyclopedia
In the study of diffraction and antenna design, the near field is that part of the radiated field that is within one quarter of a wavelength of the diffracting edge or the antenna. Beyond the near field is the far field.
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Near field
The term near-field region (also known as the near field or near zone) has the following meanings with respect to different telecommunications technologies:
- The close-in region of an antenna where the angular field distribution is dependent upon the distance from the antenna.
- 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.
- In optical fiber communications, the region close to a source or aperture.
The diffraction pattern in the near field typically differs significantly from that observed at infinity and varies with distance from the source.
Far field
The far-field region is the region outside the near-field region, where the angular field distribution is essentially independent of distance from the source. 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 2D²/λ from the source, λ being the wavelength.
For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Other synonyms are far field, far zone, and radiation field.
See also
- Local effects
- Fresnel diffraction for more on the near field
- Fraunhofer diffraction for more on the far field
- Near Field Communication for more on near field communication technology
- Other
- Ground waves is a mode of propagation.
- Sky waves is a mode of propagation.
Patents
- Leydorf, G. F., Template:US patent, Antenna near field coupling system. 1966.