In the radar's receiver two signals compete: the echo from the target and the jammer's noise. Whichever is stronger wins. A jammer flying along with the target wins at long range, but loses as the radar gets closer.
In practiceOn a SEAD mission, jamming aircraft such as the EA-18G Growler fly with the strike package. Planners work out at what range the enemy radars will burn through, and set the route and weapon release so that the attackers stay outside that range for as long as possible.
Jamming is not an on/off switch but a trial of strength. The radar receives two things at once: the echo from the target (the signal, S) and the jammer's interference (the jamming, J). The J/S ratio (jamming-to-signal) decides who wins: if J is much larger than S, the target drowns in the noise; if S becomes larger than J, the radar sees the target again — this is called burn-through.
The crucial point is the difference in how each depends on range. The target echo travels the path twice (out to the target and back) and therefore weakens with R⁴ (Radar). The signal from an accompanying (self-screening) jammer travels the path once and weakens only with R². That makes such a jammer astonishingly effective at a distance — but as the target approaches, the R⁴ echo rapidly overtakes the R² jamming, and the radar breaks through.
The burn-through range is the range at which the radar starts to see through the jamming. For an accompanying jammer (simplified):
Rbt = √( (J/S)required · Pt · Gt · σ · (Bj/Br) / (4π · ERPjammer) )
Play with the values and you will recognise the trade-offs from Stand-off vs stand-in jamming:
- More jammer ERP → a shorter burn-through range: the radar has to come closer before it breaks through. This is exactly the advantage of stand-in jamming: being close effectively means a higher ERP at the radar.
- Wider jammer bandwidth (high Bj/Br, e.g. barrage jamming) → a longer burn-through range: the power is spread out, so less of it falls within the radar's narrow band. Narrow (spot) jamming is therefore more effective per watt.
- Larger RCS or a more powerful radar → a longer burn-through range: a strong radar against a large target “burns” through sooner.
SEAD/DEAD is where everything comes together: passive homing in the ARM (Missile Guidance), electronic attack as soft kill (Electronic Counter Measures), the operator's dilemma around emission control (Doctrine & EMSO), and the hard physics of J/S and burn-through (Radar). The key lesson for the EW specialist: because of the R²-versus-R⁴ law, an accompanying jammer is disproportionately powerful — whoever understands the geometry and the J/S balance understands why air defences can be suppressed without destroying every system.