DefenseTech
Dec 7, 2007
The Poor Man's Stealth Detector
cheap-stealth.jpg
Details of a formerly secret project to defend Swedish airspace against
stealthy cruise missiles using a radical but inexpensive radar system were
revealed at a conference in Oslo this week. The Associative Aperture
Synthesis Radar (AASR) was approaching the hardware-test stage when it was
cancelled in 2000 after eight years of work -- because there was no imminent
cruise-missile threat any more. It has only recently been declassified and
this was one of the first open, formal briefings on the project.
The AASR was designed to take advantage of the principle that a target's
bistatic radar cross section -- where the radar receiver and transmitter are
in different places -- may be affected minimally or not at all by stealth
measures aimed at conventional radars. In particular, it exploits the
"shadow" RCS behind the target, which depends entirely on the target's
geometrical cross-section. The radar was also designed to operate in the UHF
band where radar absorbent material (RAM) is less effective.
Developer Hans Hellsten of Saab Microwave Systems told the conference that
the AASR used a number of novel techniques. Each transmitter would transmit
on stepped frequencies so that receivers could tell where a signal came
from. This made it possible to determine the length of the signal path, so
that if a signal was picked up at several nodes it was possible to determine
the target's location precisely.
One disadvantage: the transmitter and receiver had to be on opposite sides
of the target, so it could not be detected until it had entered the defended
airspace. To get around that problem and still intercept targets in a timely
manner, Swedish planners expected to exploit the system's accuracy -- it
could locate targets within 1.5 m -- and command-guide a high-speed missile
on to the target.
But because the system used range rather than bearing to locate its targets,
the antennas did not need to have accurate bearing resolution. Also, the
system's use of UHF, its independence from target RCS and the fact that
bistatic systems have long pulse times meant that the necessary power was
modest.
The result was a price that caused sharp intakes of breath among the
delegates. Each of the 900 nodes was expected to cost no more than 1 million
Swedish kroner (about $156,000) and the entire system would be in the 1
billion kroner ($156 million) realm -- pretty much chickenfeed by defense
standards.
Read more from our Aviation Week friends at Military.com.
-- Christian
December 7, 2007 08:06 AM
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