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From: henry@zoo.toronto.edu (Henry Spencer)
Newsgroups: sci.military
Subject: Re: Airborne Radar
Message-ID: <1991Mar4.211916.9162@cbnews.att.com>
Date: 4 Mar 91 21:19:16 GMT
References: <1991Feb28.052606.10693@cbnews.att.com> <1991Mar1.053903.944@cbnews.att.com>
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From: henry@zoo.toronto.edu (Henry Spencer)
>From: nak%archie@att.att.com (Neil A Kirby)
>Video footage shows that the entire disk on the E-3 AWACS rotates.  I'm not
>sure about the hawkeye.

Likewise.  At least one of the earlier Navy radar aircraft had a fixed
radome with a rotating antenna inside, but that approach was discarded
as inferior.

>Most modern fighters used phased array grids in the nose.

Actually, most modern fighters use mechanically-scanned flat-plate antennas.
True phased-array antennas, with all or most of the scanning done by phase
shifting, are just starting to be practical for fighters.  The problem with
phased arrays is all the electronics needed to make them work; modern
semiconductors are just now getting to the point of making them viable for
combat aircraft.

It's easy to be confused by the flat-plate antennas.  These can be
considered as phased arrays that point in one fixed direction, at right
angles to the plate.  Building this kind of antenna is not that big a
deal; it's making the phase relationships, and hence the beam direction,
variable that costs heavily in electronics.  The flat-plate antennas have
various advantages over the old dish antennas, but they share the property
that they have to be mechanically scanned.

I think the only combat aircraft in active service that has a phased-array
antenna is the B-1B, which got a significant reduction in head-on radar 
cross-section out of replacing the B-1A's dish with a phased-array antenna
tilted somewhat downward.  Several of the next-generation fighter radars
are planned to be phased arrays, but I don't believe any of them is flying
yet.
-- 
"But this *is* the simplified version   | Henry Spencer @ U of Toronto Zoology
for the general public."     -S. Harris |  henry@zoo.toronto.edu  utzoo!henry