Re: Can LPI be assisted by intentional noise generation?
- From: "Eunometic" <eunometic@xxxxxxxxxxxx>
- Date: 31 Aug 2006 07:41:49 -0700
Mike Dennis wrote:
"eponymous cowherd" <no@xxxxxxxxxxx> wrote in message
news:no-BC04F2.18215329082006@xxxxxxxxxxxxxxxxxxx
LPI radar is supposed to emit pseudo-noise which is meant to resemble
the peaks and valleys of background radiation. No matter how random the
LPI's emissions, it will still raise the overall level of radiation.
Could the effectiveness of LPI be increased by having AWACs, satellites,
etc, emit randomly rising and falling levels of radiation across the
spectrum, thus making it more difficult to notice the increase caused by
an LPI radar?
This is exactly correct. Think of the reverse scenario: How easy would it
be to pick up LPI
when there's no background noise?
Decreasing the S/N signal to noise ratio by raising the noise level
would surely work, however it could backfire.
Imagine instead of a radar warning receiver a 'radiometer' or
radiometers pinpoint the noisy radiation sources and then analyses
them. If the signals and their location were recorded and he
reflections they cause recorded it might be possible to build up the
envirnoment and track objects in the same way that some radars can use
mobile phone towers, TV and radio stations.
The radiation source then becomes more of a light source.
In WW2 the germans actually used chain home low emisions to opperate a
very effective early warning radar system.
If you think that is fare fetched than think again: some German guy
working in the US has actually worked out how to make gallium arsenide
intergrated circuits. That apparently means that analog to digital
conveters and microprocessors can be constructed that are so fast that
it is not necessary to have an analog front end. All the demodulation
and signal processing could be done digitally. It will have a big
effect on AESA style radars as well.
LPI isn't just spread spectrum. Using an active array antena means
that the systems is not reliant on a predicable raster scan or spiral
scan but builts up its pattern randomely.
To understand spread spectrum you must understand fourier series and
the Fast Fourier Transform. Any arbitray waverform can be described by
a series of sine and cosine waves of various freqencies, phases and
amplitudes. Perhaps thousands of them. Imagine all of these
modulated to carry the signal or pulse. Unless the 'enemy' knows the
pseudo random sequence generating these and unless synchronised with it
he will have trouble locating these thousands of freqencies or
demodulating them or distinquishing them from the background noise.
There are other ways as well. Impulse radar for instance.
.
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