They are especially dangerous because they can clutter up a radar with false targets making it easier for an attacker to get within weapons range and neutralize the radar. Corner reflectors can be fitted on decoys to make them appear larger than they are, thus furthering the illusion that a decoy is an actual aircraft. Some decoys have the capability to perform electronic jamming or drop chaff. Decoys also have a deliberately sacrificial purpose i.e. defenders may fire guided missiles at the decoys, thereby depleting limited stocks of expensive weaponry which might otherwise have been used against genuine targets. Electronic jamming Electronic jamming is a form of electronic warfare where jammers radiate interfering signals toward an enemy's radar, blocking the receiver with highly concentrated energy signals. The two main technique styles are noise techniques and repeater techniques. The three types of noise jamming are spot, sweep, and barrage. Spot jamming or spot noise occurs when a jammer focuses all of its power on a single frequency. This overwhelms the reflection of the original radar signal off the targets, the "skin return" or "skin reflection", making it impossible to pick out the target on the radar display. This technique is only useful against radars that broadcast on a single frequency, and can be countered by changing the frequency or other operational parameters like the pulse repetition frequency (PRF) so the jammer is no longer broadcasting on the same frequency or at the right times. While multiple jammers could possibly jam a range of frequencies, this would consume many resources and be of little effect against modern frequency-agile radars that constantly change their broadcasts. Sweep jamming is a modification of spot jamming where the jammer's full power is shifted from one frequency to another. While this has the advantage of being able to jam multiple frequencies in quick succession, it does not affect them all at the same time, and thus limits the effectiveness of this type of jamming. Although, depending on the error checking in the device this can render a wide range of devices effectively useless. Barrage jamming is a further modification of sweep jamming in which the jammer changes frequencies so rapidly it appears to be a constant radiator across its entire bandwidth. The advantage is that multiple frequencies can be jammed essentially simultaneously. The first effective barrage jammer was introduced as the carcinotron in the early 1950s, and