3.5 Complex Targets. Calculation Technique of Scattering …
45
Element RCS values, approximated by simple bodies, are easily calculated
according to abovementioned formulas. The main calculation difficulties arise at
RCS determination of complex elements (air inlet, engine nozzle). They are defined,
as a rule, experimentally or via calculation on computer.
The next calculation stage concludes in RCS calculation of a target according to
the known RCS of its parts. Let it be N number of such elements, RCS each of them
in direction γ i
i = 1, p
will be A n (γ i ), n = 1, N .
It is obvious that required RCS can be found using the following equation:
A(γ i ) =
N
n=1
A n (γ i ) exp
− jψ n (γ i )
2
,
(3.57)
where ψ n (γ i ) is field phase, reflected from element in direction γ i .
Calculations according to (3.57) formula are quite easily fulfilled if a body RCS is
changed a little in the selected sector of observation angles. In this case, an amount of
directions can be selected as equal to one, two, and required determination accuracy
of reflected field phase is comparatively low.
If complex body dimensions comprise hundreds of wavelength, and its BSD is
strongly interference in this sector of observation angles, then calculations according
to (3.57) formula become almost non-executable.
If we assume in (3.57) formula that reflected field phases from complex body
elements are interdependent random values and density of probability distribution
ψ n (γ 1 ) for all n is uniform in interval [0, 2π ], then RCS average value of such body
will be:
A =
1
N
N
n=1
A n (γ i ).
(3.58)
At fulfillment of mentioned conditions, we can find standard deviation value σ of
complex body RCS value from its average value:
σ ∼ =
A
2 −
A
2 =
1
N
N
n=1
A 2
n (γ i )
2
−
N
n=1
A n (γ i )
2
.
Since a hardly determined phase value ψ n (γ 1 ) of fields, reflected from separate
elements, is not included in calculating formula, calculations on examined technique
happen to be not complicated for arbitrary bodies, and hence, it has become widely
used in engineering practice.
The knowledge of RCS value spread of complex body, determined via examined technique, is of vital importance. Representation on its value can be obtained,
assuming that RCS of all elements is similar, i.e., A n (γ i ) = A 0 . Then, the required
(confidential) interval can be quite easily calculated and seemed to be equal to:
45
Element RCS values, approximated by simple bodies, are easily calculated
according to abovementioned formulas. The main calculation difficulties arise at
RCS determination of complex elements (air inlet, engine nozzle). They are defined,
as a rule, experimentally or via calculation on computer.
The next calculation stage concludes in RCS calculation of a target according to
the known RCS of its parts. Let it be N number of such elements, RCS each of them
in direction γ i
i = 1, p
will be A n (γ i ), n = 1, N .
It is obvious that required RCS can be found using the following equation:
A(γ i ) =
N
n=1
A n (γ i ) exp
− jψ n (γ i )
2
,
(3.57)
where ψ n (γ i ) is field phase, reflected from element in direction γ i .
Calculations according to (3.57) formula are quite easily fulfilled if a body RCS is
changed a little in the selected sector of observation angles. In this case, an amount of
directions can be selected as equal to one, two, and required determination accuracy
of reflected field phase is comparatively low.
If complex body dimensions comprise hundreds of wavelength, and its BSD is
strongly interference in this sector of observation angles, then calculations according
to (3.57) formula become almost non-executable.
If we assume in (3.57) formula that reflected field phases from complex body
elements are interdependent random values and density of probability distribution
ψ n (γ 1 ) for all n is uniform in interval [0, 2π ], then RCS average value of such body
will be:
A =
1
N
N
n=1
A n (γ i ).
(3.58)
At fulfillment of mentioned conditions, we can find standard deviation value σ of
complex body RCS value from its average value:
σ ∼ =
A
2 −
A
2 =
1
N
N
n=1
A 2
n (γ i )
2
−
N
n=1
A n (γ i )
2
.
Since a hardly determined phase value ψ n (γ 1 ) of fields, reflected from separate
elements, is not included in calculating formula, calculations on examined technique
happen to be not complicated for arbitrary bodies, and hence, it has become widely
used in engineering practice.
The knowledge of RCS value spread of complex body, determined via examined technique, is of vital importance. Representation on its value can be obtained,
assuming that RCS of all elements is similar, i.e., A n (γ i ) = A 0 . Then, the required
(confidential) interval can be quite easily calculated and seemed to be equal to: