Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!linac!att!cbnews!cbnews!military
From: mmitchel@msd.gatech.edu (Mark A. Mitchell)
Newsgroups: sci.military
Subject: Re: Airborne Radar
Message-ID: <1991Mar4.211320.8298@cbnews.att.com>
Date: 4 Mar 91 21:13:20 GMT
References: <1991Feb28.052606.10693@cbnews.att.com>
Sender: military@cbnews.att.com (william.b.thacker)
Organization: Ramblin' Wrecks from Georgia Tech
Lines: 58
Approved: military@att.att.com



From: mmitchel@msd.gatech.edu (Mark A. Mitchell)

yarvin-norman@CS.YALE.EDU (Norman Yarvin) wrote:
}
}                                     First, in a radar searching for
}airplanes, to get a three-dimensional picture the beam must be scanned over
}all combinations of two angles.

Precise radars are rarely used for hemispherical searches.  Most systems
or implacements or ships (etc.) have multiple systems: search radars,
target acquisition radars, and target track radars.  (The first two functions
and even all three are sometimes combined.)  The typical search radar 
rotates in azimuth and has a "fan" beam of some sort in elevation to
cover most of a hemisphere (generally speaking, angles close to the zenith
are ignored.)

}                                                     Do many of them simply
}not determine height?  Do they determine height in some other manner than
}scanning the beam TV-style?

Yes, some simple search radars do not determine height or elevation angle.
Many do, however, and there are a number of ways to acheive this.  One
method is a set of stacked elevation beams.  Phased arrays and frequency-
scanned arrays used this method.  A number of other methods are described
in [1].

}Second, radars on fighters seem to be located in the nose cone, and to point
}forward.  The AWACS planes seem to have a large radar, in the shape of a
}disc attached to the top of the plane.  What is the mechanism these radars
}use to scan their beams?  I know of two classes of mechanisms: phased-array
}grids, and the rotation of an antenna.

Those are probably the predominant methods.  There are others, such as
frequency-scanning, frequency-selective scanning lenses, feed scanning,
etc.  [1] provides more detail than most anyone could need.

}                                                                 Is the
}AWACS's disk shielding a rotating antenna?  And what sort of mechanism can
}fit in a fighter's nose?

Yes, the AWACS disk is a rotating radome and search antenna.  Phased-arrays,
mechanically scanned reflectors, and mechanically scanned (non-phased-)
arrays are used in the nosecones of fighter aircraft.

}Second, the limit on a radar's range is due to a combination of antenna
}geometry and output power.  Is it the AWACS's superior antenna or its higher
}power that gives it range advantages over fighter radars?

Both, but especially the antenna size and unlimited azimuth scan.

[1] _Microwave_Scanning_Antennas_,_Vol._I_, ed. R.C. Hansen, Peninsula
    Publishing, Los Altos, CA, 1985, pp. 163-165.
     
--
"If all else fails, immortality can always |  Mark A. Mitchell  Georgia Tech 
 be assured by a spectacular error."       |  mmitchel@msd.gatech.edu