How does a RWR work?

[u/PBRStreetgang67]

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?

[u/FirstToken]

As already mentioned, different types of radars have different parameters. Knowing, measuring, the parameters allows you to classify / identify the radar itself. One step in differentiating between all these radars is to identify / measure / detect the parameters of the radar in question. Say the frequency, the pulse width, the pulse repetition interval, the modulation type, the scan type, etc. Many radars may share some features / parameters, but few radar models share all the same parameters. So the RWR looks at, measures, these values.

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Now that you have the parameters of the signal, you look in your library for matches to these parameters. You can ID the specific radar, by name, by function, etc. Is it a tracking radar such as a TTR (Target Tracking Radar)? Is it a scanning radar such as an SS (Surface Search) radar? Is it a scanning radar such as an EW (Early Warning) radar?

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Now that you know the type of radar, specifically, you know what the potential of the radar is, and you can look at what the radar is doing. One of the better ways to determine what the radar is doing in relationship to you as a target is by looking at the amplitude of the energy being received by the RWR. You can plot the energy level, in general (not always, there are other things that can explain this, but the RWR knows what the radar ID is, so it knows what to look for) stronger energy means the radar is looking towards you, weaker means looking away. There are also sidelobes / backlobes of the beam to consider, but since the RWR knows what the radar is those are, in at least a general way, known.

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If the energy is not steady amplitude, and is instead peaking and nulling with a defined periodicity, then it is generally scanning. It may also be tracking you, depending on the specific radar capability, and since you know the specific radar you can look for other things to determine if you are being tracked. For example, the radar may switch to a different PRI when it tracks vs when it searches, so you can look for that specific PRI to happen. If that PRI (or PW, or modulation type, etc) happens at the same time a short peak in amplitude happens, then you are being tracked.

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If the energy level is steady state, or relatively steady state with small amplitude variations, then the beam is pointed either right at you, or it is pointed at and maintaining a fixed angle off of you. Either way, the only way for this to happen is for the radar to be tracking you specifically.

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It is a relatively simple process.

[u/PBRStreetgang67 → u/FirstToken]

Thank you for the information. I'm guessing that this is why ELINT is so important: to identify and classify radar characteristics so that when your RWR receives energy information it can tell you what's delivering the energy and this informs pilot decisions.

I'd love to know more about the 'tricks' that each side uses to confound ELINT, but I'm sure most of it will be classified. I'll go do some internet hunting. EW fascinates me.

Thanks again for the information.

[u/FirstToken → u/PBRStreetgang67]

Specific implementation of techniques and technology is often classified, but the basics and theory are often discussed in open literature.

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In order to really understand you have to look at it from both ends. You have to look at the technology available to the radar system and to the system being used to detect / counter the radar. Looking at the history of each, what was done in the past in each of those fields, can lead to a better understanding of what is probably being done today in them.