Military radars are also subject to direct attack by conventional weapons or by antiradiation missiles (ARMs) that use radar transmissions to find the target and home in on it. ECM can consist of (1) noise jamming that enters the receiver via the antenna and increases the noise level at the input of the receiver, (2) false target generation, or repeater jamming, by which hostile jammers introduce additional signals into the radar receiver in an attempt to confuse the receiver into thinking that they are real target echoes, (3) chaff, which is an artificial cloud consisting of a large number of tiny metallic reflecting strips that create strong echoes over a large area to mask the presence of real target echoes or to create confusion, and (4) decoys, which are small, inexpensive air vehicles or other objects designed to appear to the radar as if they are real targets. The purpose of hostile electronic countermeasures (ECM) is to degrade the effectiveness of military radar deliberately. Electronic countermeasures (electronic warfare) Interference is not as easily ignored by automatic detection and tracking systems, however, and so some method is usually needed to recognize and remove interference pulses before they enter the automatic detector and tracker of a radar. Well-trained operators are not often deceived by interference, though they may find it a nuisance. Signals from nearby radars and other transmitters can be strong enough to enter a radar receiver and produce spurious responses. Loss of radar energy due to atmospheric absorption, when propagation is through the clear atmosphere or rain, is usually small for most systems operating at microwave frequencies. Since it is not predictable or reliable, ducting can in some instances be more of a nuisance than a help. This results in the formation of what are called radar holes in the coverage. Ducts can sometimes extend the range of an airborne radar, but on other occasions they may cause the radar energy to be diverted and not illuminate regions below the ducts. Ducting over water is more likely to occur in tropical climates than in colder regions. The atmosphere can form “ducts” that trap and guide radar energy around the curvature of the Earth and allow detection at ranges beyond the normal horizon. This usually increases the detection range at low angles to a slight extent. The decrease in density of the Earth’s atmosphere with increasing altitude causes radar waves to bend as they propagate through the atmosphere. There are other atmospheric phenomena that can affect radar performance as well. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!Īs was mentioned, rain and other forms of precipitation can cause echo signals that mask the desired target echoes.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.
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