Graphics Programs Reference
In-Depth Information
(
SNR
)
CI
=
n
P
(
SNR
)
1
(1.82)
Coherent integration cannot be applied over a large number of pulses, partic-
ularly if the target RCS is varying rapidly. If the target radial velocity is known
and no acceleration is assumed, the maximum coherent integration time is lim-
ited to
t
CI
=
λ 2
a
r
⁄
(1.83)
where is the radar wavelength and is the target radial acceleration. Coher-
ent integration time can be extended if the target radial acceleration can be
compensated for by the radar.
λ
a
r
1.7.2. Non-Coherent Integration
Non-coherent integration is often implemented after the envelope detector,
also known as the quadratic detector. Non-coherent integration is less efficient
than coherent integration. Actually, the non-coherent integration gain is always
smaller than the number of non-coherently integrated pulses. This loss in inte-
gration is referred to as post detection or square law detect
o
r loss. Marcum and
Swerling showed that this loss is somewhere between
and
. DiFranco
n
P
n
P
and Rubin presented an approximation of this loss as
L
NCI
=
10
log
(
n
p
)
5.5
dB
(1.84)
Note that as
becomes very large, the integration loss approaches
.
n
P
n
P
The subject of integration loss is treated in great levels of detail in the litera-
ture. Different authors use different approximations for the integration loss
associated with non-coherent integration. However, all these different approxi-
mations yield very comparable results. Therefore, in the opinion of these
authors the use of one formula or another to approximate integration loss
becomes somewhat subjective. In this topic, the integration loss approximation
reported by Barton and used by Curry will be adopted. In this case, the non-
coherent integration loss which can be used in the radar equation is
1
+
SNR
(
SNR
)
1
L
NCI
=
----------------------------
(1.85)
(
)
1
It follows that the SNR when
pulses are integrated non-coherently is
n
P
(
SNR
)
1
n
P
(
SNR
)
1
----------------------------
(
SNR
)
NCI
=
-------------------------
=
n
P
(
SNR
)
1
×
(1.86)
L
NCI
1
+
(
SNR
)
1
1.7.3. Detection Range with Pulse Integration
The process of determining the radar sensitivity or equivalently the maxi-
mum detection range when pulse integration is used is as follows: First, decide
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