Phased array radars

[B2431]

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

[Jake McGuire]

(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?

Phased arrays might buy you 60 degrees of beam steering each way. If
you want 360 degree coverage you need multiple arrays like on the
TICOs and BURKEs, or you can rotate one array. In the latter case, a
phased array buys you scanning in elevation to determine target
altitude, and if you're sneaky you can scan side to side independently
of the antenna rotation as an ECCM technique.

-jake

[Regnirps]

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

[B2431]

>From: (Regnirps)
>
<snip>

>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

Civilian colour weather radar sets show up occasionally on e-bay. As a matter
of fact that's what got me to finally break down and ask the question.

Dan, U.S. Air Force, retired

[The Enlightenment]

"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

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.

[Jim Yanik]

(B2431) wrote in
:

>>From: (Regnirps)
>>
><snip>
>
>>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
>
> Civilian colour weather radar sets show up occasionally on e-bay. As a
> matter of fact that's what got me to finally break down and ask the
> question.
>
> Dan, U.S. Air Force, retired

Uh,I don't believe weather radars are phased arrays. It would be
overkill,and an unnecessary expense.

The color part come from computer processing of the radar return

--
Jim Yanik
jyanik-at-kua.net

[Keith Willshaw]

"Jim Yanik" > wrote in message
.. .
> (B2431) wrote in
> :

> Uh,I don't believe weather radars are phased arrays. It would be
> overkill,and an unnecessary expense.
>

http://www.oudaily.com/vnews/display.v/ART/2003/04/28/3eaca4e76e2d2?in_archive=1

Keith

[B2431]

>From: Jim Yanik

>
(B2431) wrote in
:
>
>>>From: (Regnirps)
>>>
>><snip>
>>
>>>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
>>
>> Civilian colour weather radar sets show up occasionally on e-bay. As a
>> matter of fact that's what got me to finally break down and ask the
>> question.
>>
>> Dan, U.S. Air Force, retired
>
>Uh,I don't believe weather radars are phased arrays. It would be
>overkill,and an unnecessary expense.
>
>The color part come from computer processing of the radar return
>
>--
>Jim Yanik
>jyanik-at-kua.net

I could be wrong about its function, but there was a phased array system for
civil aircraft on e-bay a week or so ago.

Dan, U.S. Air Force, retired

[Jim Yanik]

"Keith Willshaw" > wrote in
:

> http://www.oudaily.com/vnews/display.v/ART/2003/04/28/3eaca4e76e2d2?in_
> archive=1
>

This article says that the phased array radar is NEW in this
application(weather radar),and was just introduced at a first site.

I may have ASSumed that he was referring to weather radar used by TV
stations and metrological stations,not airborne civilian aircraft
instrumentation.

Apologies.


--
Jim Yanik
jyanik-at-kua.net

[Howard Berkowitz]

In article >, Jim Yanik
> wrote:

> "Keith Willshaw" > wrote in
> :
>
> > http://www.oudaily.com/vnews/display.v/ART/2003/04/28/3eaca4e76e2d2?in_
> > archive=1
> >
>
> This article says that the phased array radar is NEW in this
> application(weather radar),and was just introduced at a first site.
>
> I may have ASSumed that he was referring to weather radar used by TV
> stations and metrological stations,not airborne civilian aircraft
> instrumentation.
>
> Apologies.

Maybe eBay spelled it wrong, and it was an old, fazed radar sold by
somebody's buddy A. Ray, who used to be run a radar in an EC-121 or the
like? I tell ya, it's pitiful to see a hard-working radar, that didn't
plan for retirement, up on the auction block. Radars like that don't
believe in reality any more, just thinking life is nothing but
reflections.

[Harry Andreas]

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

[Harry Andreas]

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

[David McArthur]

(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