radar missile frequency
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Posted by Adam Chapman on May 13, 2008, 2:10 pm
Please log in for more thread options 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 | ||||||||||||||||||||||||||||||||||
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Posted by Adam Chapman on May 13, 2008, 2:20 pm
Please log in for more thread options sorry i should have noted taht the high absortion at 60 and 120GHz is due to the resonant frequency of oxygen in the atmosphere | ||||||||||||||||||||||||||||||||||
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Posted by Bert Hyman on May 13, 2008, 2:20 pm
Please log in for more thread options adam.chapman@student.manchester.ac.uk (Adam Chapman) wrote in
> 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 | ||||||||||||||||||||||||||||||||||
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Posted by Adam Chapman on May 13, 2008, 2:29 pm
Please log in for more thread options > 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 | ||||||||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on May 14, 2008, 1:10 am
Please log in for more thread options On Tue, 13 May 2008 11:10:46 -0700 (PDT), Adam Chapman
>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>
The earlier versions are laser guided.
<http://en.wikipedia.org/wiki/AGM-114_Hellfire> <http://www.janes.com/defence/air_forces/news/jalw/jalw001013_1_n.shtml> <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 | ||||||||||||||||||||||||||||||||||
>
> 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