ES (Electromagnetic Support) senses and characterizes emissions. EP (Electromagnetic Protection) makes our own systems resistant. EA (Electromagnetic Attack) jams, deceives, or destroys threat sensors.
You cannot jam intelligently a signal you have not first intercepted and characterized.
It does not break it. It adds its own received power to the noise, so the receiver works only when \(S/(N + J) \ge SNR_{\min}\) — the same \(SNR_{\min}\) as with the jammer off. The jamming dwarfs the thermal noise \(N\), so in practice the test is \(S/J \ge SNR_{\min}\).
The ratio of two Friis calculations into the same receiver: \(SNR_\text{comm} = \dfrac{P_{T,\text{sig}}G_{T,\text{sig}}G_R\lambda^2/(4\pi R_\text{sig})^2}{P_{T,\text{jam}}G_{T,\text{jam}}G_R\lambda^2/(4\pi R_\text{jam})^2}\).
\(G_R\), \(\lambda^2\), and \((4\pi)^2\) all cancel, leaving the equation sheet's row, \(SNR_\text{comm} = P_{T,\text{sig}}G_{T,\text{sig}}R_\text{jam}^2/(P_{T,\text{jam}}G_{T,\text{jam}}R_\text{sig}^2)\). The reading writes \(R_\text{txrx}\) for \(R_\text{sig}\).
That the receive antenna has the same gain toward both the transmitter and the jammer, and that the jammer is on the victim's frequency, inside its bandwidth. A receive antenna that nulls the jammer's bearing breaks it. What is left to fight over is power, gain, and above all the ratio of ranges, squared.
The victim receiver. \(R_\text{sig}\) runs from the transmitter to it and \(R_\text{jam}\) from the jammer to it — never from the jammer to the transmitter.
Because \(SNR_\text{comm} \propto R_\text{jam}^2\). A jammer twice as far away is four times less effective. Geometry beats power.
The echo (radar range equation) over the jamming (Friis into the radar's own antenna): \(SNR_\text{rad} = \dfrac{P_T\,G_T\,RCS}{P_{T,\text{jam}}\,G_{T,\text{jam}}\,4\pi R^2}\). It assumes the jammer is at the target's range: self-screening (the target carries it) or an escort flying with the target, so one \(R\) serves both paths. True stand-off radar jamming needs two ranges, which is outside this course.
The jammer's signal travels one way (\(1/R^2\)) while the radar's echo travels two (\(1/R^4\)). So \(SNR_\text{rad} \propto 1/R^2\): far out the jamming wins, and the echo gains on it only as the target closes.
The range at which \(SNR_\text{rad}\) reaches the radar's \(SNR_{\min}\): \(R_{BT} = \sqrt{\dfrac{P_T\,G_T\,RCS}{P_{T,\text{jam}}\,G_{T,\text{jam}}\,4\pi\,SNR_{\min}}}\), in meters because \(RCS\) is in m². Inside it the radar sees through the jamming.
It does not move the radar equation's detection range. It adds a second, tighter limit, the burn-through range: a jammed radar detects only inside it.
The aircraft is never closer to the radar than its own altitude (30,000 ft is \(30{,}000 \times 0.305 = 9{,}150\) m), so that range is never reached: the radar never burns through. A small burn-through range is a jammer that works, not a mistake.
Spread spectrum (power density below the noise floor), frequency hopping, power management (transmit the least that closes the link), and narrow beams.
Because \(SNR_\text{comm}\) is only linear in \(P_{T,\text{sig}}\) but goes as the square of range. Shortening the link, or using EP so the jammer cannot concentrate power in your band, buys far more.
Chaff (false returns), flares (IR decoys), towed and active decoys, and anti-radiation missiles that home on the radar's own emissions.