The RWR is a set of ears around the aircraft. It hears radars, recognises them by their "voice" and tells the crew who is looking, from which direction and how dangerous it is.
In practiceIn the cockpit a search radar ticks now and then, a lock becomes a continuous tone and a launch sounds a different alarm. The pilot reacts: changing course, using the jammer or chaff, or manoeuvring. Helicopters and transport aircraft have an RWR too.
The Radar Warning Receiver is the most widespread ESM system: a set of wideband antennas around the platform (typically four, one per quadrant), receivers and a processor that listens continuously for radar emissions and warns the crew: who is illuminating me, from where, and how dangerous is it?
What the RWR extracts from every intercepted emission:
- Identity: frequency, PRF/PRI, PW and scan characteristics (Pulse radar) against the library → radar type and associated weapon system.
- Direction: amplitude or phase comparison between the antennas → a bearing (coarse, but good enough to react and to point jammers/decoys).
- Mode — the most important: from the PRF, waveform and illumination pattern the RWR deduces what the radar is doing (Target tracking by radar: the Target Tracking Radar): an occasional sweep = search; frequent, directed illumination = acquisition; continuous illumination at high PRF = track/lock; CW illumination or an approaching new emitter = missile guidance (Semi-Active Radar Homing, Active Radar Homing). Each step means the opponent's fire control sequence (The fire control sequence) is progressing.
The presentation: an azimuth display around an own-platform symbol, with threat symbols at their bearing (priority towards the centre), plus audio — the classic soundscape in which a search radar "ticks" and a lock becomes a continuous tone. The RWR prioritises: a tracking fire-control radar at short range shouts, a distant early warning radar (Characteristics of the Early Warning (EW) radar) whispers.
| RWR hears… | Meaning | Typical response |
|---|---|---|
| search sweeps (low PRF, periodic) | someone is searching; you are (still) a plot | reconsider route/altitude, EMCON |
| acquisition (more frequent, directed) | a TTR is trying to catch you (Target acquisition and tracking) | manoeuvre, terrain masking, jammer ready |
| lock / track (continuous, high PRF) | a fire-control solution is being built | break manoeuvre, ECM programme, chaff |
| CW / missile guidance / "pitbull" | a weapon is on its way (Homing guidance) | last-second manoeuvre + expendables/decoy |
Limitations — and therefore additions: an RWR only hears what transmits. A passive IR missile (Passive homing), a fully passively guided attack or an LPI radar (Frequency Modulated Continuous Wave radar) does not appear on the display, or appears late. In dense signal environments the RWR also has to untangle thousands of pulses per second (de-interleaving), and its bearing is too coarse for weapon employment. That is why it never stands alone: the MAWS (Missile Approach Warning System) sees what the RWR cannot hear, and together they feed the countermeasures computer that controls the whole package from Electronic Counter Measures.