On 21 May 2004 19:14:11 GMT, (B2431) wrote:

I have seen phased array aircraft radars that look as if they still
mechanically sweep the dish. I thought the entire reason for phased arrays was
so they wouldn't need to mechanically move. I know how phased arrays work in
principle, but that's as far as I go. What am I missing here?

The basic reason is that the apparent size (area) of the array goes down by the
cosine of the angle off center. That means resolution and the amount of
reflected energy it can "see" degrades unless you can point the plane of the
array at the object of interest. Uhm, cosine of 45 degrees is .707 (something
from high school about holding your arms like swept wings and thinking Boeing
707 : ) so that isn't too bad but by 60 degrees you have cut the apparent size
in half.

There is also today some rather advanced processing in small packages
(naturally) that used to be on big platforms and sats. The example that comes
to mind is "spotlighting", which uses synthetic aperture type processing and
tracks an object or ground target getting more information with each ping.
Ultimately, image reconstruction methods similar to tomography can be used to
build a picture of the target. In spotlighting the ground you can get a great
picture. If an air target stays on heading there can be a pretty good picture
of that too.

Anyway, for these to work well the plane of the array needs to be normal to the
target. I'm just amazed the darn things work so well, and when will I be able
to get one surplus?

-- Charlie Springer