The early warning radar stands at the front of the chain: warn as early as possible, coarsely if need be. Every design choice follows from that single task — and can be explained entirely with Radar:
| Characteristic | Typical choice | Why (reference) |
|---|---|---|
| Frequency | low: VHF/UHF/L-band | little attenuation → long range; a long wavelength is also better against stealth (Frequency bands) |
| Transmit power | very high | range costs power to the 4th power (Inverse square law) |
| PRF | low (hundreds of Hz) | large maximum unambiguous range: R = c/(2·PRF) (Maximum Unambiguous Range) |
| Pulse width | long, with pulse compression | a lot of energy per pulse for range; compression saves the resolution (Pulse compression and pulse integration) |
| Antenna | large, fan beam, often 2D | wide elevation coverage; height is not needed in this phase (2D and 3D radar) |
| Scan rate | slow (5–12 revolutions/min) | long time-on-target per revolution → pulse integration (Pulse compression and pulse integration) |
| Accuracy | coarse (degrees, hundreds of metres) | only needs to be good enough to cue a tracker |
The result: detection ranges of 300–500 km or more against conventional targets. The weaknesses are the mirror images of the strengths: coarse resolution (several targets merge, Angular resolution), slow updates (a fast target covers kilometres between two revolutions), vulnerability to low flyers below the radar horizon, and — inevitably — an enormous, continuous emission that ESM can see at an even greater distance than the radar's own range.
EW radars are the "tripwire" of an integrated air defence system (IADS). For mission planning their position and frequency band tell you: where can you get through low/masked, and from which point on have you been seen? Their low frequencies also make them hard to jam with self-protection jammers, which are built mainly for tracker bands.
