January 10, 2011 · 1:57 am
AESAs
aim their "beam" by broadcasting radio energy that interfere
constructively at certain angles in front of the antenna. They improve
on the older passive electronically scanned radars by spreading their
broadcasts out across a band of frequencies, which makes it very
difficult to detect over background noise. AESAs allow ships and
aircraft to broadcast powerful radar signals while still remaining
stealthy. Above is AESA on F22
The AN/APG-77 is a multifunction radar installed on
the F-22 Raptor fighter aircraft. It is one of the most advanced radar
today. More than 100 APG-77 AESA radars have been produced to date by
Northrop Grumman, and much of the technology developed for the APG-77 is
being used in the APG-81 radar for the F-35 Lightning II. The APG-77v1
was installed on F-22 Raptors from Lot 5 and on. This provided full
air-to-ground functionality (high-resolution synthetic aperture radar
mapping, ground moving target indication and track (GMTI/GMTT),
automatic cueing and recognition, combat identification, and many other
advanced features).
APG-77 is based on Active Electronically Steered
Array (AESA) technology. The AESA includes multiple individual active
transmit/receive (T/R) elements within the antenna. Depending upon the
precise implementation, there may be anywhere between 1000 and 2000 of
these individual T/R elements which, together with the RF feed, comprise
the AESA antenna. As for the passive ESA, these elements are highly
redundant and the radar can continue to operate with a sizeable
percentage of the devices inoperative. This graceful redundancy feature
means that the radar antenna is extremely reliable; it has been claimed
that an AESA antenna will outlast the host aircraft. The fact that the
transmitter elements reside in the antenna itself means there is no
standalone transmitter – there is an exciter but that is all. As before,
there is clearly a need for a receiver as well as an RDP and signal
processor. The active T/R elements are controlled in the same way as the
phase shifters on the passive ESA, either by using a beam-steering
computer (BSC) or by embedding the beam-steering function in the RDP.
The ability to control many individual T/R modules
by software means confers the AESA with immense flexibility of which
only a few examples are: First each radiating element may be
controlled in terms of amplitude and phase, and this provides superior
beam-shaping capabilities for advanced radar modes such as
terrainfollowing, synthetic aperture radar (SAR) and inverse SAR (ISAR)
modes. Secondly Multiple independently steered beams may be configured using partitioned parts of the multidevice array. Thirdly
If suitable care is taken in the design of the T/R module, independent
steerable beams operating on different frequencies may be accommodated
and Finally The signal losses experienced by the individual T/R
cell approach used in the AESA also bring considerable advantages in
noise reduction, and this is reflected in improved radar performance.
The
AN/APG-80 system is described as "agile beam", and can perform
air-to-air, search-and-track, air-to-ground targeting and aircraft
terrain-following functions simultaneously and for multiple targets. As a
SAR system utilizing NG's fourth-generation transmitter/receiver
technologies, it has a higher reliability and twice the range of older,
mechanically-scanned AN/APG-68 radar systems. Above is F-16 APG-80 Radar
One dramatic improvement is the noise figure; it is
especially significant achieving such an improvement so early in the RF
front end. This results in a remarkable range improvement for the AESA
radar. A number of US fighter aircraft are being fitted or retrofitted
with AESA radars, these are F-22 Raptor, F-18E/F (Upgrade version)
fitted with AN/APG-79, F-16E/F (Block 60) fitted with AN/APG-80, F-15
and F-35 fitted with AN/APG-81. Taking for example F-16, it is
interesting to see a dofference in performance between two batches
(Block 50) and Block 60. Former had target detection radar range of 50
miles, which was improved to 70 miles with AESA radards (for reference
F-22 covers 125miles range). The F-16 Block 60 (now the F-16E/F) shows
an improvement from 45 to 70 nm (þ55%), while the F-15C range has
increased from 60 to 90 nm (þ50%). Apart from the obvious improvement in
range, it has been stated by a highly authentic source that AESA radar
confers 10–30 times more in radar operational capability compared with a
conventional radar (Report of the Defense Science Board Task Force,
2001).
The F-16E (single seat) and F-16F (two seat) are
newer F-16 variants. The Block 60 version is based on the F-16C/D Block
50/52 and has been developed especially for the United Arab Emirates
(UAE). It features improved AN/APG-80 Active Electronically Scanned
Array (AESA) radar, avionics, conformal fuel tanks (CFTs), and the more
powerful GE F110-132 engine. However the batch bought by Pakistan Air
Force (F-16C/D) is equipped with AN/APG-68 (V)9 Radar Systems. Only the
Block 60 aircraft, destined for the UAE, are to be equipped with a more
advanced version – the Active Electronically Scanned Array (AESA) radar.
The APG-68(V)9 offers 30 percent increase in detection range, improved
search-while-track mode (four vs. two tracked targets) and larger search
volume and improved track while scan performance. Its single target
track performance has also been improved. On air/ground missions, the
new radar becomes an effective sensor, utilizing its high-resolution
synthetic aperture radar mode, which allows the pilot to locate and
recognize tactical ground targets from considerable distances. Although
previous radars had some Synthetic Aperture Radar (SAR) capabilities,
the new version generates imagery-class (2 feet resolution) high
resolutions pictures, comparable to pictures delivered by the most
modern commercial satellites. These pictures can be acquired from very
long range, at all weather conditions and provide an effective,
real-time source for the targeting of long range, precision guided
weapons. The radar also has increased detection range in sea
surveillance mode, and enhanced ground moving target identification and
mapping capability. The radar features an inertial measurement unit that
improves dynamic tracking performance and provides an auto-boresight
capability, which increases accuracy.
Red Storm Rising
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