Barrage jamming

"Barrage" refers to systems that send signals in many bands of frequencies compared to the bandwidth of any single radar.

Early barrage jammers in World War II used photomultiplier tubes to amplify a wideband noise source,[1] An improved approach appeared with the introduction of the carcinotron in the early 1950s, a vacuum tube that generates microwaves whose frequency can be adjusted across a very wide band simply by changing the input voltage.

Combining this with extremely powerful signals and highly focused antennas allowed new radars to overpower the jammers, "burning through" the jamming.

Simple techniques, like turning off the receivers when the antenna was pointed close to the jammer, allowed the radar to continue tracking other targets.

A well developed instance of this was deployed by the RAF in their RX12874 network, which could track jammer-carrying aircraft with accuracy equal to a radar.

This image shows the effect of four carcinotron-carrying aircraft on a typical 1950s early warning radar. The aircraft are located at the 4 and 6 o'clock positions, which are completely filled with noise.