Near and far field
From Free net encyclopedia
←Older revision | Newer revision→
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.
Contents |
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.