Graphics Programs Reference
In-Depth Information
The choice of an operating frequency that can fulfill the design requirements
is driven by many factors, such as aperture size, antenna gain, clutter, atmo-
spheric attenuation, and the maximum peak power, to name a few. In this
design, an operating frequency is selected. This choice is somewhat
arbitrary at this point; however, as we proceed with the design process this
choice will be better clarified.
f
=
3
GHz
Second, the transportability (mobility) of the radar drives the designer in the
direction of a smaller aperture type. A good choice would be less than 5 meters
squared. For now choose . The last issue that one must consider is
the energy required per pulse. Note that this design approach assumes that the
minimum detection SNR (13 dB) requirement is based on pulse integration.
This condition is true because the target is illuminated with several pulses dur-
ing a single scan, provided that the antenna azimuth beamwidth and the PRF
choice satisfy Eq. (1.81).
2.25
m
2
A
e
=
The single pulse energy is . Typically, a given radar must be
designed such that it has a handful of pulsewidths (waveforms) to choose from.
Different waveforms (pulsewidths) are used for definite modes of operations
(search, track, etc.). However, for now only a single pulse which satisfies the
range resolution requirement is considered. To calculate the minimum single
pulse energy required for proper detection, use Eq. (1.57). More precisely,
E
=
t
τ
4(
3
kT
e
FLR
4
SNR
1
G
2
λ
2
σ
E
t
τ
=
=
---------------------------------------------------
(1.92)
All parameters in Eq. (1.92) are known, except for the antenna gain, the detec-
tion range, and the single pulse SNR. The antenna gain is calculated from
4π
A
e
λ
2
4π 2.25
×
0.1
G
=
------------
=
-----------------------
=
2827.4
⇒
G
=
34.5
dB
(1.93)
)
2
(
where the relation (
λ
=
cf
⁄
) was used.
In order to estimate the detection range, consider the following argument.
Since an aircraft has a larger RCS than a missile, one would expect an aircraft
to be detected at a much longer range than that of a missile. This is depicted in
missile detection range. As illustrated in this figure, the minimum search ele-
vation angle is driven by the missile detection range, assuming that the mis-
siles are detected, with the proper SNR, as soon as they enter the radar beam.
Alternatively, the maximum search elevation angle is driven the aircraftÓs
position along with the range that corresponds to the defenseÓs last chance to
intercept the threat (both aircraft and missile). This range is often called Ðkeep-
out minimum rangeÑ and is denoted by
R
a
R
m
θ
1
θ
2
R
min
. In this design approach,
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