Re: [OT] Longbow Hellfire (was Re: GMS Air)

Christopher Ruhl wrote:
> I'll leave the final call to some of the brighter list members, but
from all the literature I've read on the Longbow system, the
millimetric-wave radar is a passive system.  I know it seems
contradictory, but it is supposed to detect the disturbances in radio
frequencies caused by large masses like tanks and have the definition
to identify them by type.

	I'm pretty sure the radar is active but incorporates a passive
receiver system as your following quote points out:

> My immediate reference for this is Army Technology's Apache entry at
<http://www.army-technology.com/projects/apache/index.html> under the
heading of Missiles ("The Longbow fire control radar incorporates an
integrated radar frequency interferometer for passive location and
identification of radar emitting threats.

	Note that the radar _incorporates_ the interferometer? Basically
it
can "hear" radar "pings", a passive sensor. With the interferometer, it
can then give an angle/bearing to the source of the ping, much like
knowing where a sound comes from, when using your ears.

> An advantage of millimetre wave is that it performs under poor
visibility conditions and is less sensitive to ground clutter. The
short wavelength allows a very narrow beamwidth which is resistant to
countermeasures.").

	Here's what the radar send out, when it goes active, MMW.

So basically the radar is in passive mode "listening" for opposing
radar "pings". When in active mode, the radar sends out a "ping" of MMW
energy in the desired arc and "listens" for echoes. The MMW Hellfire is
ARH, but, I believe, it can travel along a bearing, flying blind, so as
to minimise enemy response time to the active radar homing "pings" the
missile itself can send and receive.

Andrew Martin
Al.Bri@xtra.co.nz
http://members.xoom.com/AndrewMartin/
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