Phased array radars

In article , Glenfiddich
wrote:

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?

A flat phased array antenna can instantly swing its beam
electronically to point *anywhere* ahead but can NOT look
'behind' the plane of the antenna array. And its efficiency
falls off as it squints to extreme port or starboard...

Therefore, to get 'all-round' coverage you either add more arrays
(facing left, right and rear, as you see on the bridge structure of
many modern ships) - or physically swing the one antenna you already
have.

Adding a turntable to a single antenna sounds like an engineer's
answer to the design problem.
A simple, robust rotator, being very 'old-tech', is probably a lot
cheaper and more reliable than 3 more arrays...

OK for big platforms like AWACS or E-2C, but problematic for fast-movers.
From an engineering standpoint...

--
Harry Andreas
Engineering raconteur

In article , "The
Enlightenment" wrote:

Some phased arrays rotate but and are only phase steered in the
vertical for height finding purposes. For instance the antenna on
US AWACS aircraft use this technique, though the Israeli AWACS use
fixed antena inside the dome.

This technique goes back to the 2nd world war. (I think the German
radars Wassermann and Jagdschloss used it as did the radars for the
Soviet missiles SA1 and SA2)

Alternatively and cluster of 4 antena as seen on the USN Aegis system
can be used. There must be great difficulty in integrating the 4
antena to work together.

Having a phased array is pretty important these days. Modern fighter
tactics involve splitting in such a way that the enemy can not track
the multiple targets with a mechanical antenna anymore and using this
as an opportunity to attack.

As with most things, there are pro's and con's.
AESAs let you track more targets effectively instantly, when the nose is
pointed in the right direction.
But a mechanically scanned array has a larger off-boresite look angle.
Above statements for fighter aircraft, not surveillance types.

--
Harry Andreas
Engineering raconteur

(B2431) wrote in message ...
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?

Dan, U.S. Air Force, retired

The new Sampson phased array on the UK's Type 45 is a rotating 2-faced
array - think it rotates at around 60 rpm.
David