Figure 1: Constellation for stand-off jamming
Support Jamming is the term for a procedure in which the jammer supports the attack by jamming from a stand-off area. The jamming power therefore usually acts via a sidelobe of the radar’s antenna radiation pattern and is therefore also called sidelobe jamming. Depending on the size of this sidelobe, the jamming power must be much larger than by self-protection or escort jamming. With a sidelobe size of -20 dB on average, the jammer must provide 20 dB more jamming power, which in this case means 100 times more power output. (This is why keeping the size of the sidelobes as small as possible is also an essential performance characteristic for a radar).
According to the free-space path loss, this necessary jamming power is also distance-dependent. If sufficient power reserves are available, the jammer can operate farther away from the radar, thus farther away than the attack force to be protected. This constellation is called stand-off jamming (SOJ). It has the advantage that the jammer is relatively safe from attack far away from the combat action. The disadvantage is that the jamming effect is reduced due to the long distance or a higher transmitting power must be applied.
If only low power reserves are available, the jammer must operate at a shorter range than the attack force. He is thus more at risk, but the jamming power is more effective, and the attack aircraft is better protected. This constellation is called stand-in jamming (SIJ).
- EIRPJam = equivalent isotropic radiated power of the jammer;
- EIRPRadar = equivalent isotropic radiated power of the radar transmitter;
- RJ = distance radar - jammer [m]
- RT = distance radar - attack aircraft [m]
- σ = radar cross section (RCS) of the attack aircraft [m²]
Compared to self-protection or escort jamming, this equation additionally includes the side-lobe attenuation and the ratio of the different ranges. For the jamming carrier, the simple free-space path loss applies with the square of the range; for the radar, the free-space path loss applies to both the outbound and return paths, hence the fourth power of the range.