OpenRA - Red Alert Wiki

The Mobile Radar Jammer defends nearby units against many missiles. Any guided missile is affected. This includes the missiles of: MiGs, submarines, mammoth tanks, chrono tanks, Longbows, etc. If it's homing - it's affected.

The Mobile Radar Jammer can jam an enemy's radar dome by getting sufficiently close. This will hide the enemy's minimap, as if the dome is powered down. When a players radar dome gets jammed, a powered down sound is played.

The unit has 2 circles around it indicating the effect radiuses. The smaller red one is the radius where missiles are deflected, the larger blue shows the radius for jamming the radar dome.

Mobile radar jammer effect radius

Mobile Radar Jammer effect radiuses while deflecting the missiles of a MiG.