Path: utzoo!utgpu!watserv1!watmath!att!cbnews!military
Newsgroups: sci.military
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Message-ID: <1990Sep2.061113.3550@cbnews.att.com>
Date: 2 Sep 90 06:11:13 GMT
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From: sun!sunburn.West.Sun.COM!gtx!qip!john (John Moore)
Subject: Re: Anti-radiation missle capabilities?
Keith Lewis (lewis@saint) writes:
]
]In article <1990Aug21.024249.220@cbnews.att.com> Will Martin <wmartin@STL-06SIMA.ARMY.MIL> writes:
]
]>Can anti-radiation missiles, which usually are used against radars operating
]>in the UHF or microwave range, be used against targets emitting lower
]>frequencies, like HF radio? Could such a missile be used to home in on the
]>antenna of a transmitter being used to jam shortwave broadcast reception,
]>for example?
]
]In order to home in on a transmitting antenna, the missile needs a recieving
]antenna (or three) of its own.  The size of a given design of antenna
]is some fraction (preferably 1) of the wavelength (inversly proportional
]to the frequency) of the broadcast you want to home in on.  Radar is
]measured in centimeters.  HF is measured in meters.  So for *Optimal*
]design, you would make the antennae a number of meters in size.
]
]Whether you really need this optimization I can't say.  There may be other
]designs that are effective, or maybe the radar antennae will work *well enough*
]to take out a powerful transmitting antenna.

You definitely don't. Consider a hand-held transistor radio. It is
quite sensitive, but has an antenna about .5"x.5"x4". It is also
extremely directional. You can verify this by orienting the
long part of the loopstick antenna towards a radio station. When it
is precisely lined up, the station will fade out.

Likewise, a Loran C receiver operates on 100 KHz, which is a wavelength
of 3000 meters. I have seen them with small vertical antennas.

Small aperture antennas are not very directional, except where symmetry
causes a cancellation effect. Hence, a seeker head using this would
be a bit tricky - probably requiring moving parts, and would be 
sensitive to multiple signal sources.  However, for pulsed radars, 
it should be possible to discriminate between the multiple sources.

John Moore   asuvax!anasaz!john