[extropy-chat] LASER: DARPA's HELLADS small laser weapon makes headway

[J. Andrew Rogers]

On 9/2/05 3:34 AM, "Eugen Leitl" <eugen at leitl.org> wrote:
> On Thu, Sep 01, 2005 at 11:44:34PM -0700, J. Andrew Rogers wrote:
> 
>> State-of-the-art active radar systems do not detectably radiate at all,
>> another very, very slick piece of American military technology.  It is how
> 
> I don't see how this is supposed to be possible. Are you sure you're not
> meaning passive radar?


Nope, not passive radar, though on some levels it shares principles.  I am
not an authority on the details of it, and the real details are classified.

The problem with passive radar is that you do not control the
characteristics or power of the radiator that is illuminating the target, so
one has to measure background and then do cross-correlation to find patterns
allowing for variation and uncertainty in the reference.  This limits range
and resolution.  This new type of active radar uses an ultra-wide band
radiator that mimics background RF in all respects, but since the computer
has perfect knowledge of the background 'noise', it can extract far more
detail at far more range than traditional passive radar.

A few advanced countries are using UWB radar for their weapon systems, which
is much more resistant to ECM than traditional radar and is harder to detect
at a distance due to the lower power in a given band.  However, most of
these systems still generate a signature that an advanced ECM package could
detect.  The special feature the US state-of-the-art UWB radar used in
stealthy systems is that the mimicry of background RF is supposedly nearly
perfect such that you can be looking directly at it at quite close range and
never see it unless you have the 'key' required to decrypt the background RF
one is looking at.  In short, by the time the other guy has a prayer of
detecting the radiator, you will be in visual range (and the other guy will
have long since died).  And of course, these same platforms can also be
keyed off of AWACs and other external radiators for some proper passive
radar.

I guess this would be an example of an almost perfectly efficient RF data
communication technology, though not used as such in the radar application.


As I said, I don't know all the technical details beyond what I've gleaned
from radar tech guys who've worked on a lot of military radar systems.
Supposedly this is an incremental evolutionary convergence of advanced RF
technology that the US has been perfecting for a long time.  The radar
packages used in many more conventional combat aircraft platforms use UWB
radiators, but in a more traditional low probability of intercept
configuration that can be detected if the ED/ECM is very slick, due
primarily to the fact that it does not look like background RF noise.


J. Andrew Rogers