"John Larkin" wrote in message
...
On Wed, 22 Aug 2007 17:17:23 +0800, "Tom Potter"
wrote:


"John Larkin" wrote in
message
. ..
On Tue, 21 Aug 2007 15:41:13 -0500,
(Hal Murray) wrote:

No, but I have enough years of experience with RF in general and radar
in particular to know building a phased array requires precise phase
(or frequency) control and you can't do that with an ultra wideband
device, which has a bandwidth of 500 Mhz.

At a minumum!


What is the bandwidth of modern radars? I'd expect it to be
wide and using spread spectrum tricks to make jaming harder.

Spiffy modern radars hop and chirp, both of which broaden the working
bandwidth.

With modern signal processing, wider radar bandwidth improves
resolution. You can do all sorts of fun stuff with 1000 antennas and a
few teraflops of compute power.

All the major powers - US, Russia, France, Germany, China, Israel, UK
- are working on HPM weapons and array radars. The Brits call their
projects "Suave" and "Virus." MBDA and BAE are major players.

Google "mbda hpm" and "bae hpm", and believe it or don't.

John

It seems to me,
that with modern electronics and information technology,
that a high resolution, handheld, RADAR system is possible.

You could quasi-randomly modulate (Variable transmit and listen periods),
a solid state microwave oscillator (Gunn Diode)
with a digital code with good correlation properties (Gold Code),

cross-correlate the echoes received when in the listen mode
with the Gold Code, then cross-correlate the correlations
from the echoes with stored geo-patterns downloaded
from a Google-Earth like data base covering the area of operation,

compare adjacent (In time) echo returns to spot moving targets,
then present the pattern on a small, solid state, color display
that shows the Google-Earth like picture of the area,
with super-imposed moving targets.

One would not need a directional antenna,
nor high power for such a device,
but it would be necessary to sweep the device around
to build up a good correlation of
the area as one's body and other things
would block the signals and,
even though the Google-Earth like picture,
and the location of the RADAR would still be valid,
but blocked moving targets would not be detected.

Note that if a map of the area of operation is downloaded
into the system, and a set of times from the radar to fixed
targets is compared to the map, one could quickly correlate the
map with the echoes and determine where one is.

With such a device, one could move around,
and see where they were on a moving Google-Earth-like picture,
and see the moving targets about them,
perhaps even colored and shaped by the RADAR signatures
of the targets. (People, cars, tanks, trains, an incoming missle, etc.)

Note that for many situations that such a device could replace GPS.
Just like GPS, after the device determines where one is,
it would be able to compute changes in position quickly.

Hey maybe, I should patent this device?


I'd like to have a short-range imaging radar, sort of like my Flir
handheld thermal imager, as a sort of super stud finder.

Imagine a pc board covered with etched patch antennas, one or more
step-recovery-diode impulse generators, and a lot of sampling
receivers. Run it at several MHz, do a lot of averaging and signal
processing, and reconstruct the image. Maybe use Wii type
accelerometers so as the array is moved around, additional signal
paths can be crunched in to enhance resolution without blurring. The
microwave side of the hardware would be dirt cheap, and the signal
processing would have a high engineering cost but would also be cheap
in production.

Take a look at McEwan's patents for an idea of how the hardware would
work. He was mostly looking at stuff like auto collision detection,
1-dimensional ranging, but imaging is quite feasible if you dump
enough DSP onto the problem.

Firemen could use this for smoke penetration, or cops could spot bad
guys in the next room, and I could spot cats under beds without having
to crawl around on the floor.

John

Note that John's idea for a hand-held RADAR
differs from mine.

The one I propose would use Google Maps
to correlate with the RADAR data, and to display
where the user was, and the moving targets about him,

whereas John's RADAR would be provide a two,
and perhaps three dimensional picture of the
targets in its' range.

John's RADAR would use techniques like those
used in medical imaging I suppose.

--
Tom Potter

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