Wind Turbines and stealth

"David McArthur" wrote in message
om...
Interesting piece on Radio 4 this morn (UK): Wind turbines apparently
play havoc with ATC radars.
Qinetiq, the UK defence research agency is looking at a solution:-
Adding 'electromagnetic elements' between some of the layers of the
glass fibre.
The chap they were interviewing from Qinetiq said that the result was
"Destructive Interference" causing the cancelling out of the radar
energy.

...I wonder if this is some military stealth concepts making the jump
to civilan applications.

Comments?

A quick Google shows that there is a fair amount of comment on the general
problem: http://www.qinetiq.com/casestudies/2003/case_study.html and
http://www.countryguardian.net/modradar.htm , for starters. This is probably
the best report I found on the Web:
http://www.bwea.com/aviation/ams_report.html (Incidentally, this last has a
three-part PDF report and an excellent HTML summary).

Some of the problems evidently have been solved using existing (known)
techniques - filtering through electronics and software. The Doppler return
from a wind turbine resembles that of a/c (more to the point, apparently
most ATC radars just pick up Doppler; they don't do fine analysis of the
Doppler, though), but the object itself is not moving, so they simply do
so-called "plot" or "track" filtering.

As an aside, it makes me wonder if a helicopter hovering would then not also
completely get filtered out by an ATC radar? It's been 2 decades since I
took antenna theory and electronics, so I have no idea. But it's an
interesting speculation.

I think the remaining problem that they are trying to solve is the possible
large radar cross-section of a wind-turbine. Add in the fact that one
actually typically has entire wind-farms, and one has such a large return
that discriminating out a much smaller Doppler signal in the vicinity
becomes quite difficult. I don't grok the actual scope of the problem, but
according to what I gather from the articles, solving this problem by
modifying radar installations is much more labour-intensive and costly than
mitigating the Doppler return problem. So I am not surprised to hear that
they are looking at using turbine material mods to reduce RCS.

AHS