Page 298 - Radar Technology Encyclopedia

noise, quantization NOMENCLATURE, radar 288

Quantization noise is noise arising from the conversion of speckle noise (see SPECKLE).
sampled voltages into the integer numbers in analog-to-digi-
Target noise is the fluctuation in amplitude, location, and
tal converters. This noise is the source of random error addi-
doppler caused by the target, excluding atmospheric effects.
tional to the errors caused by the noise in analogous networks
Typically, target noise includes amplitude noise, angle noise,
of radar receiver. SAL
range noise, and doppler scintillation. (See also FLUCTUA-
Ref.: Skolnik (1990), p. 3.40.
TION, GLINT.) SAL
Range noise is “the noise-like variation in the apparent dis- Ref.: IEEE (1990), p. 29; Skolnik (1990), p. 18.34.
tance of the target, caused by changes in amplitude and phase
noise temperature (see TEMPERATURE).
of the target-scattering sources, and including radial compo-
nents of glint and scintillation error.” Range noise is similar to Thermal noise is noise generated by the thermal motion of
angle noise. It can also result in an error greater than the wan- the conduction electrons in tubes or solid-state components of
der of the target center of gravity, can fall outside the target radar receivers. The power of this noise is directly propor-
span, can be a major limitation to the accuracy of velocity tional to the temperature of the ohmic portions of the circuit
obtained from range rate, and can cause angle-tracking errors and the receiver bandwidth (see noise power). Thermal noise
in multilateration systems that use high-precision range mea- is the main source of uncertainty resulting in fundamental
surements. A beacon installed on a target can eliminate an inability of error-free radar operation in real conditions, as it
error arising from range noise, provided it has very stable cir- results in arising of errors when radar operates in any of its
cuitry avoiding pulse jitter and drift. (See also ERROR.) SAL modes, performing detection, measurement, or discrimination
function. Thermal noise sometimes is called Johnson noise.
Ref.: Skolnik (1990), p. 18.45.
SAL
Rayleigh noise is the noise described by the random process
Ref.: Skolnik (1980), p. 18.
with the Rayleigh distribution of probability density function:
2
æ
ö
u
u
æ
u ö
W ------ = ------exp – ç --------- ÷u ³, 0 tracking noise (see ERROR, measurement).
è s ø s 2
n n è 2s ø Urban noise is noise arising from automobile ignition, power
tools, and other man-made sources of unintentional interfer-
= 0 u <, 0 ence. It can affect radars operating at low frequencies. SAL
2
where u is instantaneous noise voltage and s is noise vari- Ref.: Skolnik (1980), p. 463.
n
ance. The envelope of receiver noise, consisting of two White noise is a random process having the uniform spec-
quadrature components of Gaussian noise, has a Rayleigh dis- trum density at all frequencies, and correspondingly, a delta-
tribution. AIL function-type correlation function. This means that any two
Ref.: Barton (1964), p. 11; Svistov (1977), p. 866. values of white noise in any two moments of time regardless
of how close they are to each other, are always independent
Servo noise is the noise arising from different mechanical
(uncorrelated). Theoretically, white noise has an infinite spec-
instabilities of servomechanisms in radars employing
trum but in practical applications any noise in the passband of
mechanical scanning. The sources of this noise, which limits
a real radar circuit can be presented as white because the
angular accuracy in some tracking radars, are backlash and
passband is always finite and the out-of-the-band components
compliance in the gears, shafts, and structures of the mount.
do not affect the circuit. White noise is termed so by analogy
SAL
with the white light that has an approximately uniform spec-
Ref.: Skolnik (1980), p. 170.
trum within its visible range. AIL
Shot noise is the fluctuation of electronic current or ionic
Ref.: Barton (1964), p. 323; Kazarinov (1990), p. 19.
emission caused by the continuous changing of the number
electrons or ions being emitted when the structure of the emit- NOMENCLATURE, radar. The radar nomenclature system
ting surface is unchanged. It is the main source of internal used in U.S. military equipment was developed during World
noise of microwave amplifiers due to current fluctuations in War II, and is formally entitled the Joint Electronics Types
the process of electron emission. AIL Designation System (JETDS). It is described by Military
Standard MIL-STD-196D and was formerly known as the
Ref.: Chistyakov (1986), p. 23; Fink (1982), p. 4.4.
Joint Army-Navy Nomenclature System or AN System, Table
Solar noise is the environmental noise arising from electro-
N2. The designation begins with the letters AN, followed by a
magnetic radiation emitted by sun. Its power, unlike most
slash and three additional letters from Table N2 specifying
other noise sources, increases with frequency, and in some
where the equipment is installed, its type, and purpose. The
cases it can affect radars with low-noise receivers. SAL
final numerical value indicates the order in which the equip-
Ref.: Skolnik (1980), p. 463.
ment was placed into development or entered into the nomen-
A noise source is a device employed for generation of noise clature system. Other systems of designation are used for civil
in ECM technique. Usually, these are different types of radars and those of non-U.S. origin. SAL
microwave tubes and solid-state devices. SAL Ref.: Skolnik (1990), p. 1.19.
Ref.: Johnston (1979), p. 64.