3.1 Types of Radar Targets
21
Thus, reflected from a real target signal due to influence of a set of factors is a
random, fluctuated signal. On a fluctuated useful signal, an another random process
is overlapped—noises and interference—which results in formation of random value
“signal + noise,” perceived by the radar receiving device. Therefore, for quantitative
assessments of both a value of inherent reflected signal and results of its influence
on the radar, a machinery of probability theory is initiated.
3.2 Radar Cross Section of Radar Targets
Let the radar radiates through antenna with G gain factor and electromagnetic wave
of P power. Then, a value of power flow density near a target, located at R distance
from antenna, will be as follows:
rad =
P G
4π R 2 .
(3.2)
It is obvious that in direction to antenna, a wave will scatter the power of which P sct
is proportional to P rad value, defined by (3.2) equation. Herewith, a proportionality
factor should have an area dimension. Let us denote it A, then P sct = A rad , and so,
a power flow density of scattered wave P sct near antenna will be defined using the
following equation:
sct =
P sct
4π R 2 = A
rad
4π R 2 = A
P G
4π R 2
2 .
(3.3)
As a value is proportional to squared absolute value of electric vector, then
from (3.2.) and (3.3) equations, we will have the following:
A = 4π R
2 sct
rad
= 4π R
2 E
2
sct
E
2
rad
.
(3.4)
An advantage of introduced A parameter concludes in that it does not depend on
distance, though it included in (3.3) formula in an explicit form. This is explained
by the fact that E sct is proportional to E rad /R value, so therefore A is defined only
by a target. A factor (coefficient) A is called an effective scattering cross section
(area)/radar cross section (RCS) or an effective reflective area (ERA) and is one
of the main characteristics of radar targets.
At varying mutual position of antenna and target, the RCS will obviously be
changing. Dependence of RCS from azimuth and elevation angle is called a backscattering diagram (BSD). For the purpose to calculate RCS and BSD, it is necessary to
solve a corresponding diffraction problem that is connected with calculation difficulties; hence, here, we found a wide application to different approximation methods.
Let us examine them.
21
Thus, reflected from a real target signal due to influence of a set of factors is a
random, fluctuated signal. On a fluctuated useful signal, an another random process
is overlapped—noises and interference—which results in formation of random value
“signal + noise,” perceived by the radar receiving device. Therefore, for quantitative
assessments of both a value of inherent reflected signal and results of its influence
on the radar, a machinery of probability theory is initiated.
3.2 Radar Cross Section of Radar Targets
Let the radar radiates through antenna with G gain factor and electromagnetic wave
of P power. Then, a value of power flow density near a target, located at R distance
from antenna, will be as follows:
rad =
P G
4π R 2 .
(3.2)
It is obvious that in direction to antenna, a wave will scatter the power of which P sct
is proportional to P rad value, defined by (3.2) equation. Herewith, a proportionality
factor should have an area dimension. Let us denote it A, then P sct = A rad , and so,
a power flow density of scattered wave P sct near antenna will be defined using the
following equation:
sct =
P sct
4π R 2 = A
rad
4π R 2 = A
P G
4π R 2
2 .
(3.3)
As a value is proportional to squared absolute value of electric vector, then
from (3.2.) and (3.3) equations, we will have the following:
A = 4π R
2 sct
rad
= 4π R
2 E
2
sct
E
2
rad
.
(3.4)
An advantage of introduced A parameter concludes in that it does not depend on
distance, though it included in (3.3) formula in an explicit form. This is explained
by the fact that E sct is proportional to E rad /R value, so therefore A is defined only
by a target. A factor (coefficient) A is called an effective scattering cross section
(area)/radar cross section (RCS) or an effective reflective area (ERA) and is one
of the main characteristics of radar targets.
At varying mutual position of antenna and target, the RCS will obviously be
changing. Dependence of RCS from azimuth and elevation angle is called a backscattering diagram (BSD). For the purpose to calculate RCS and BSD, it is necessary to
solve a corresponding diffraction problem that is connected with calculation difficulties; hence, here, we found a wide application to different approximation methods.
Let us examine them.