Science Fair Project Encyclopedia
Electronic countermeasures (ECM) are any sort of electrical or electronic device designed to "spoof" radar, sonar, or other detection systems. They may be used both offensively or defensively in any method to deny targeting information to an enemy. The system may make there appear to be many separate targets or make the real target appear to disappear or move about randomly. It is used effectively to protect aircrafts from guided missiles. Most air forces use them to protect their aircraft from attack.
ECM is practiced by nearly all military units — land, sea or air. Aircraft are the primary weapons in the ECM battle because they can "see" a larger patch of earth than a sea or land based unit. When employed effectively, ECM can keep aircraft from being tracked by surface-to-air missiles and air-to-air missiles.
ECM is a function of the electromagnetic spectrum or frequency of energy that is directed toward a target. Every type of radar functions in the electromagnetic spectrum and can be sensed by the proper equipment. Since radar works very much like an echo you hear if you yell into a chasm or canyon, it can be timed and identified by the frequency at which it operates. For example, if you strum an open low "A" string on a guitar, it resonates at a frequency of 440 hertz. The sound waves travel out like ripples in a pond and in all directions. When the waves reach the other side of the canyon, they are reflected or bounced back toward the source. The sound arrives at your ear after a short time and you hear the "echo". If someone on he other side of the canyon has a guitar tuned to 442 hz and they strum it as soon as they hear the sound from your guitar, their sound will reach you at approximately the same time as your echo. This combination of sounds will sound strange to you. A radar system is much more accurate while it listens for the echo. If it sends out 440 Hz, it expects to "hear" a reflected 440 Hz. If the sound comes back at 442 or 445 Hz, then the radar receiver or "ear" can be confused.
ECM deals with jamming, covering from and eliminating threats. Many sophisticated methods of jamming an electromagnetic signal exist. Covering involves overpowering a signal so that the radar receiver is overwhelmed and cannot process the echo. Elimination consists of anti-radiation missiles and bombs that home in on the radar signal and destroy the source.
Another kind of ECM is more offensive in theory. It involves using an electromagnetic pulse (EMP) to overdrive or burn out all electronics. This can be used to destroy the enemy's ability to communicate quickly, even though nowadays many communication centers, mobile or fixed, are protected against EMP. EMP is, however, also a very good psychological weapon as it renders all TVs, radios, computers and cell phones useless.
Examples of dedicated electronic countermeasures aircraft
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