The Fraunhofer distance, named after
Joseph von Fraunhofer
Joseph Ritter von Fraunhofer (; ; 6 March 1787 – 7 June 1826) was a German physicist and optical lens manufacturer. He made optical glass, an achromatic telescope, and objective lenses. He developed diffraction grating and also invented the ...
, is the value of:
:
where D is the largest dimension of the radiator (in the case of a magnetic loop
antenna, the
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...
) and
is the
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of the radio
wave
In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from List of types of equilibrium, equilibrium) of one or more quantities. ''Periodic waves'' oscillate repeatedly about an equilibrium ...
. This distance provides the limit between the
near 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. Non-radiative ''near-field'' behaviors dominate close to the an ...
, allowing for 22.5 degrees of phase deviation over the face of the radiator.
See also
*
Fresnel number
In optics, in particular scalar diffraction theory, the Fresnel number (), named after the physicist Augustin-Jean Fresnel, is a dimensionless number relating to the pattern a beam of light forms on a surface when projected through an aperture ...
*
Fresnel diffraction
In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff's diffraction formula, Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near and far field, near fi ...
and
Fraunhofer diffraction
In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when plane waves are incident on a diffracting object, and the diffraction pattern is viewed at a sufficiently long distance (a distance satisfying Fraunhofer ...
*
Antenna measurement
Antenna measurement techniques refer to the testing of antenna (radio), antennas to ensure that they meet specifications or simply to characterize them. Typical antenna parameters include Antenna gain, gain, Antenna bandwidth, bandwidth, radiation ...
References
* Eugene F. Knott, "Radar Cross Section", Second Edition
Diffraction
Antennas
Antennas (radio)
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