radar missile frequency

Hello,

First of all sorry if this is off topic, I couldn't find a group on
radar.

I was wondering why radar guided missiles use such a high frequency.
Looking at a graph I have showing atmoshperic absorbtion of radar
waves; there are two very high peaks (indicating high absorption) at
60GHz and 120GHz. This is due to resonant frequencies of atmospheric
molecules. The hellfire missile's radar seeker operates at 94GHz and
the
Apache Helicopter uses a 35GHz radar. Absorption at the helicopter's
and missile's frecuencies is fairly similar so it can't be anything
to
do will design operating range.


It must be something to do with either antenna size or resolution,
but
no idea which or why. Can anybody please point me in thre right
direction?


Thanks for any help
Adam

On May 13, 7:10*pm, Adam Chapman
<adam.chap...@student.manchester.ac.uk> wrote:
> Hello,
>
> First of all sorry if this is off topic, I couldn't find a group on
> radar.
>
> I was wondering why radar guided missiles use such a high frequency.
> Looking at a graph I have showing atmoshperic absorbtion of radar
> waves; there are two very high peaks (indicating high absorption) at
> 60GHz and 120GHz. This is due to resonant frequencies of atmospheric
> molecules. The hellfire missile's radar seeker operates at 94GHz and
> the
> Apache Helicopter uses a 35GHz radar. Absorption at the helicopter's
> and missile's frecuencies is fairly similar so it can't be anything
> to
> do will design operating range.
>
> It must be something to do with either antenna size or resolution,
> but
> no idea which or why. Can anybody please point me in thre right
> direction?
>
> Thanks for any help
> Adam

sorry i should have noted taht the high absortion at 60 and 120GHz is
due to the resonant frequency of oxygen in the atmosphere

adam.chapman@student.manchester.ac.uk (Adam Chapman) wrote in
news:229196f5-8852-45b9-ac3a-53e091c48700@m3g2000hsc.googlegroups.com:

> First of all sorry if this is off topic, I couldn't find a group on
> radar.

sci.engr.radar+sonar

--
Bert Hyman | St. Paul, MN | bert@iphouse.com

On May 13, 7:20*pm, Bert Hyman <b...@iphouse.com> wrote:
> adam.chap...@student.manchester.ac.uk (Adam Chapman) wrote innews:229196f5-8852-45b9-ac3a-53e091c48700@m3g2000hsc.googlegroups.com:
>
> > First of all sorry if this is off topic, I couldn't find a group on
> > radar.
>
> sci.engr.radar+sonar
>
> --
> Bert Hyman | St. Paul, MN | b...@iphouse.com

thanks,
didn't come up when searching google groups for "radar" for some reason

On Tue, 13 May 2008 11:10:46 -0700 (PDT), Adam Chapman
<adam.chapman@student.manchester.ac.uk> wrote:

>First of all sorry if this is off topic, I couldn't find a group on
>radar.

As others have noted:
sci.engr.radar+sonar

>I was wondering why radar guided missiles use such a high frequency.

1. Resolution. The higher the frequency, the greater the ability to
resolve detail and separate multiple objects.
2. Antenna gain. The higher the frequency, the higher the gain of a
given antenna of a fixed diameter.

>Looking at a graph I have showing atmoshperic absorbtion of radar
>waves; there are two very high peaks (indicating high absorption) at
>60GHz and 120GHz. This is due to resonant frequencies of atmospheric
>molecules. The hellfire missile's radar seeker operates at 94GHz and
>the
>Apache Helicopter uses a 35GHz radar. Absorption at the helicopter's
>and missile's frecuencies is fairly similar so it can't be anything
>to
>do will design operating range.
>It must be something to do with either antenna size or resolution,
>but
>no idea which or why. Can anybody please point me in thre right
>direction?
>

That would be the AGM-114L Longbow missile:
<http://www.fas.org/man/dod-101/sys/missile/agm-114.htm>
<http://en.wikipedia.org/wiki/AGM-114_Hellfire>
<http://www.janes.com/defence/air_forces/news/jalw/jalw001013_1_n.shtml>
The earlier versions are laser guided.

<http://www.rfcafe.com/references/electrical/atm_absorption.htm>

I'm not sure where you got your frequencies from, but the AGM-114L
runs at 94GHz at which there is minimal atmospheric attenuation. It's
the perfect place for a missile radar. The reason they switched from
optical to RF guidance is that optical does work in all weather
conditions, while 94GHz works well enough. The radar is also immune
to optical countermeasures and less susceptible to detection.

The 60 and 120Ghz frequencies are at the peaks in atmospheric
absorption. These are sometimes use for short range radar, where
stealth is important. The more atmospheric attenuation, the small the
effects of ground based radar detection or jamming. These frequencies
are also popular for communications above the atmosphere (i.e. between
orbital devices) as they cannot be sniffed by ground based receivers.

>Thanks for any help
>Adam
>
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

In <itqk249euvpcd9l0493umu3cmqsf9pulnj@4ax.com> Jeff Liebermann <jeffl@cruzio.com> writes:

>The 60 and 120Ghz frequencies are at the peaks in atmospheric
>absorption. These are sometimes use for short range radar, where
>stealth is important. The more atmospheric attenuation, the small the
>effects of ground based radar detection or jamming. These frequencies
>are also popular for communications above the atmosphere (i.e. between
>orbital devices) as they cannot be sniffed by ground based receivers.

Sure, that'll keep the Russkies from finding
them. But it won't protect us from the Ceylons.

--
__________________________________________________ ___
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

On Wed, 14 May 2008 14:03:33 +0000 (UTC), danny burstein
<dannyb@panix.com> wrote:

>Sure, that'll keep the Russkies from finding
>them. But it won't protect us from the Ceylons.

Ceylon is now known as Sri Lanka.
<http://en.wikipedia.org/wiki/Sri_Lanka>
Last time I checked, the US and Ceylon are still on good terms.

I think you mean either the old or new Cylons:
<http://en.wikipedia.org/wiki/Cylon_%28Battlestar_Galactica%29>
I'm not too worried as the US military is negotiating with Hollywood
for a license to produce the Klingon cloaking device:
<http://en.wikipedia.org/wiki/Cloaking_device>
which should restore our defensive supremacy.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In <6h3m24dlhlno39iq4pl7bupl7ucuabmalh@4ax.com> Jeff Liebermann <jeffl@cruzio.com> writes:

>I think you mean either the old or new Cylons:
><http://en.wikipedia.org/wiki/Cylon_%28Battlestar_Galactica%29>
>I'm not too worried as the US military is negotiating with Hollywood
>for a license to produce the Klingon cloaking device:
><http://en.wikipedia.org/wiki/Cloaking_device>
>which should restore our defensive supremacy.

But just remember that even an invisible
ship, when passing through a cloud, leaves
a visible trail.

And now with all the RF out there, it's a pretty hefty
cloud wherever you go.


--
__________________________________________________ ___
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Adam Chapman wrote:
> I was wondering why radar guided missiles use such a high frequency.

As I understand your question, you're asking why targeting radar
uses such high frequencies in spite of the atmospheric absorption
at those frequencies.

Electronic microscopes can discern down to only around 200 nanometers,
but an electron microscope down to 2 nanometers. Likewise 60 Gig and
higher frequency radar can discerne smaller objects than 5 Gig. And
the beam is narrower for better aiming

As for incidental attenuation, you simply avoid the ""black hole"
bands. You have water absorption bands at 22, 183 and 323 GHz, and
oxygen absorption bands at 60 and 118 GHz. So those are the frequency
ranges you don't want to use.

I had to look in my collection of books for citations.

An FCC document of NOTICE OF PROPOSED RULE MAKING "Allocations
and Service Rules for the 71-76 GHz, 81-86 GHz and 92-95 GHz
Bands" has good explanations.

Likewise "Radar Handbook" (19990) and "Radio Meteorology" (1968).

79 Gig looks good for long distance. Maybe Navas should issue a
"Warning: 79 GHz is not secure" alert.