Electromagnetic warfare (EW) is military action involving the use of electromagnetic (EM) and directed energy to control the EM spectrum or to attack the enemy.

- Electromagnetic Attack (EA) - Electromagnetic Protection (EP) - Electromagnetic Support (ES)

$$ SNR = \frac{P_{Signal}}{P_{Noise}} $$

As noise power increases, SNR decreases. A lower SNR makes communication more difficult.

Stand-off jamming is a jamming scenario where the jammer is separate from the transmitter and receiver.

$$ SNR = \frac{P_{T} G_{T} R_{jam}^{2}}{P_{jam} G_{jam} R_{txrx}^{2}} $$

- Jamming power, $P_{jam}$ - Jamming antenna gain, $G_{jam}$ - Distance to the target receiver, $R_{jam}$

As the jammer moves closer to the receiver, $R_{jam}$ decreases and SNR decreases. This makes communications jamming more effective.

- Chirp signals - Frequency hopping - Direct-sequence spread spectrum (DSSS)

A chirp signal is a signal whose carrier frequency sweeps up or down across a range of frequencies at a set rate. This provides some resistance to jamming.

Frequency hopping uses multiple carrier frequencies and a pseudo-random noise (PRN) code to jump between frequencies. The transmitter and receiver must stay synchronized.

DSSS spreads a signal over a wider bandwidth by sampling at a higher rate and multiplying by a PRN code. This makes the signal harder to detect and jam.

$$ SNR = \frac{P_{RADAR} G_{RADAR} (RCS)}{4\pi P_{jam} G_{jam} R^{2}} $$

As $R$ gets smaller, SNR gets bigger. This means RADAR jamming becomes less effective as the jammer gets closer, which is the opposite of communications jamming.

Burn through is the point where the RADAR can overcome the jamming and detect the target. It occurs when the jammer becomes ineffective.