radar missile frequency


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

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

Reply to
Adam Chapman

snipped-for-privacy@student.manchester.ac.uk (Adam Chapman) wrote in news: snipped-for-privacy@m3g2000hsc.googlegroups.com:


Reply to
Bert Hyman

- snipped-for-privacy@m3g2000hsc.googlegroups.com:

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

Reply to
Adam Chapman

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

  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.

That would be the AGM-114L Longbow missile:

The earlier versions are laser guided.

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.

Reply to
Jeff Liebermann

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

Reply to
danny burstein

Ceylon is now known as 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:

I'm not too worried as the US military is negotiating with Hollywood for a license to produce the Klingon cloaking device:

which should restore our defensive supremacy.

Reply to
Jeff Liebermann

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.

Reply to
danny burstein

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.
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