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

In article ,
David McArthur wrote:

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

Stealthing bridges and buildings isn't something new and
from this little information it's hard to tell if the
suggested solution is something suitable for aircraft,
ships or vehicles.
--
Urban Fredriksson http://www.canit.se/%7Egriffon/
Just because something is obvious doesn't mean it's true.

Urban Fredriksson wrote in message ...
In article ,
David McArthur wrote:

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

Stealthing bridges and buildings isn't something new and
from this little information it's hard to tell if the
suggested solution is something suitable for aircraft,
ships or vehicles.

Well if you can make the blades of a wind generator less visible to radar, then surely the same techniques could be applied (or have
already been applied) to reducing the Radar Cross-Section (RCS) of propellor-driven aircraft such has the Hercules or Osprey..?

In article , wrote:

In article ,
David McArthur wrote:

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

Stealthing bridges and buildings isn't something new and
from this little information it's hard to tell if the
suggested solution is something suitable for aircraft,
ships or vehicles.

Look to elementary education for stealth -- invisible playmates,
homework-eating dogs, often the homework itself, etc.

"Arved Sandstrom" wrote in message ...
"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

Thanks for the links - it sounds like an intriguing problem.
The bit that caught my attention on the interview was the specific
reference to destructive interference - I'm curious to know what sort
of materials (or arrangement of materials) would be able to produce a
phase difference(?) that would nullify the incoming radar signal?

David

David McArthur wrote:

....snipped...
Thanks for the links - it sounds like an intriguing problem.
The bit that caught my attention on the interview was the specific
reference to destructive interference - I'm curious to know what sort
of materials (or arrangement of materials) would be able to produce a
phase difference(?) that would nullify the incoming radar signal?

David

There were several consumer-oriented stealth-related books that were
published at the end of the 1980s. They should have sufficient general
details. Try:

- Stealth, Doug Richardson, Orion Books, NY, 1989.
- Stealth Aircraft, Bill Sweetman, Motorbooks International, 1986.
- Stealth Technology, J. Jones, Aero, 1989.

Or for something a bit more detailed, see:
- Radar Cross Section, Eugene F. Knott, John F. Shaeffer, Michael T.
Tuley, Artech House Radar Library, 1993, 2nd ed.

A certain David McArthur did scribble:

Thanks for the links - it sounds like an intriguing problem.
The bit that caught my attention on the interview was the specific
reference to destructive interference - I'm curious to know what sort
of materials (or arrangement of materials) would be able to produce a
phase difference(?) that would nullify the incoming radar signal?

David

The use of dielectric materials with a reflective backing with an overall
quarter wavelength thickness would suffice. For total destructive
interference you want it in antiphase, or a half wavelength out of phase. A
RAM with quarter wavelength thickness would give you this property. The
stealth books Stephen Poe listed will have a more full explanation.

--�
rgds

BMFull