In article , Jeff Liebermann writes:
Thanks and interesting. I discarded synthetic aperture imaging
because I assumed that either the sensor array or the object being
imaged had to be moving roughly perpendicular to each other. That
seems to be the case with SAR (synthetic aperture radar). I'll read
some more (later) as I have no experience with the technology.

You mean you were planning a 30,000 foot eyeball and no way to
aim it?

Yes, you are probably right - there would be issues with off-axis
imaging, especially if the individual antennas were widely spaced.

Unfortunately what I know beyond what I talked about is rather
sketchy, but I do know that synthetic apertures are used for
optical telescopes. Instead of a single, perfectly polished
mirror, you place multiple mirrors somewhat distant from one
another and use optical magic (smoke and mirrors?) to put it
all together for form an image.

Anyway, if you have a telescope mirror with holes in it, you
have tradeoffs.

I'm guessing that what happens is that there are
aliasing effects. If the spacing along, say, the
x axis, is s and wavelength is w, you will have
alaising - images of off-axis points that appear
to be on-axis, for example - and I would expect
those to be at angles

arcsin ( N w / s )

relative to the normal (read arcsin as
"the angle whose sine is")

If you want to see something that is off axis, you
might be able to leverage this if each antenna
is directional and blocks most energy from outside
a main lobe narrow enough that, for small N
at least, the antanna only picks up signals from
one of the aliased angles and blocks the adjacent
ones - kind of like an RF amp passband that allows
a desired frequency through and not its image
frequency.

And you might be able to tune the pattern so the
nulls in the pattern at least partially null
out aliases at the N-1 and N+1 angles, where
you would have to have some lobe width adjustment
if you wanted to use this technique for more
than just a single value of N.

If you don't want to use a dish, perhaps you
could use a 'Pringles can' antenna with a dipole
at the far end of a long cylinder - your "telescope
body".

You would feed measured magnitude and phase from
each antenna to your computer to have it produce
an image.

And if you were really good, and used a UHF
illumination source, you would interfere
the illumination source with the received
signals and via holographic techniques
produce true 3D.

Just speculation. But if it's doable I
would guess the military has already done it.

George