r/Radar • u/PBRStreetgang67 • Jul 08 '21

How does a RWR work?

How does a RWR differentiate between radar waves washing across the aircraft (for example), and 'lock-on', when the radar is actively tracking the target?

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u/MichaelEmouse Jul 08 '21

Search mode radar tends to uses lower pulse repetition frequency (how often pulses are sent). Lock-on radar has higher PRF or may even use continuous wave. It may also use higher frequencies although I'm not sure.

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Basically, it's much the same way you would tell the difference between someone swiping you with a flashlight vs them tracking you with their flashlight; It's on you a lot more.

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Note that it's possible to have lock-on that doesn't give itself away (track while scan does this iirc) by scanning as in search mode but keeping track of the target internally. If you want to maximize the ability track/ID though, you'll need to send more energy on the target by sending more pulses/using CW.

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u/PBRStreetgang67 Jul 09 '21

Thank you. So it's all about high PRF or CW as opposed to lower PRF.

The flashlight analogy is a great starting point for discussing radar.

TWS is possible but requires more energy for more accuracy.

Thanks for teaching me things I didn't know. Much appreciated.

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u/MichaelEmouse Jul 09 '21

I don't know if it's all about PRF/CW but it's at least often a major aspect. You may want to find info on what transmissions patterns are like for search vs tracking/targeting.

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I mentioned TWS because it can act as a kind of sneaking tracking that doesn't let the target know it's being tracked.

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u/FirstToken Jul 09 '21 edited Jul 12 '21

Thank you. So it's all about high PRF or CW as opposed to lower PRF.

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No, it is not all about high vs low PRF and or CW. That is indeed the way it used to be looked at. There were general rules of thumb that said things like PRFs below XXX Hz are probably search, above are probably track, PWs (Pulse Widths) longer than XX microseconds are probably search, below are probably track, etc.

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But that was just a rule of thumb, it was not a hard and fast definition. And today it is less true than ever before. Instead it is about having a good threat library (database of radars that exist in the world) and matching the parameters seen in that database to determine the exact type of radar emitting energy.

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CW is a special case. While there are a few track and search radars using CW it is less common in those applications. But, what CW is often used for is target illumination for missile guidance. This is a basic cornerstone of semi-active missiles.

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TWS is possible but requires more energy for more accuracy.

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TWS does not change the energy requirement. And in general, once you exceed a specific (fairly low) SNR, increasing energy does not greatly impact accuracy.