Page 274 - Electrical Engineering Dictionary

Fano algorithm a sequential decoding al- the wavelength. Also called the Fraunhofer
gorithm for decoding of trellis codes. region.

Fano mode a bound nonradiative surface far pointer a pointer to a far segment. In
mode that propagates along an interface and 80 × 86 architecture, a far pointer specifies
decays in a nonoscillatory manner in a direc- the segment address and the offset.
tion perpendicular to the propagation. Such
a mode occurs when one of the media is a far-field pattern graph or chart repre-
plasma medium and has a negative dielectric senting the absolute or normalized antenna
function. A metal at optical frequency is an gain as a function of angle (typically azimuth
example of such a medium. or elevation) and used to describe the direc-
tional properties of an antenna in the far field
Fano’s inequality information theoretic (Fraunhofer region).
inequality bounding the probability of incor-
rectly guessing the value of one random vari-
far-infrared (FIR) spectral region often
able based on observation of another. If P e considered to range from about 10 to 100 mi-
is the probability of incorrectly guessing a crometers.
random variable X ∈ X, based upon obser-
vation of the random variable Y, then
farad the basic unit of measure in capac-
itors. A capacitor charged to 1 volt with a
H (P e ) + P e log(|X − 1) ≥ H(X|Y)
charge of 1 coulomb (1 ampere flowing for
1 second) has a capacitance of 1 farad.
Named after its discoverer, R. M. Fano
(1952). Used in proving the weak converse to
Faraday effect the rotation of the plane of
the channel coding theorem (Shannon’s sec-
polarization of a high-frequency signal (mi-
ond theorem).
crowave RF, optical field) in the presence of
a magnetic field.
Fano’s limit theoretical limit relating the
achievable gain and bandwidth of a given
Faraday rotation (1) rotation in the di-
passive lossless matching network when ter-
rection of polarization experienced by a wave
minated in an arbitrary load impedance.
traveling through an anisotropic medium.
Important examples of media in which the
far field (1) that region of space in which
phenomenon occurs include the earth’s iono-
the electric field and magnetic field compo-
sphereandferritesbiasedbyastaticmagnetic
nents of an electromagnetic wave are related
field.
by the impedance of free space. The far field
is generally considered to begin no closer (2) depolarization caused in a plasma
to the NIER source than a distance of sev- (e.g., the ionosphere) resulting from interac-
eral wavelengths or several times the antenna tion between the ions of the plasma and the
aperture. magnetic field of the wave.
(2) that region of the field of a certain (3) rotation in the polarization vector
source where the angular field distribution experienced by a wave after it propagates
depends in a known way from the distance through a gyromagnetic medium.
of the source. Generally, in free space, if we
consider as a source an antenna with max- Faraday rotator a magneto-optical de-
imum overall dimension D, assumed large vice that changes the orientation plane of
compared to the wavelength, the far-field re- polarized light when it passes parallel to a
gion is commonly taken to exist at distances magnetic field through a substance with pro-
2
greater than 2D /λ from the antenna, λ being nounced absorption lines.

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2000 by CRC Press LLC