How Does Aviation Radar Work?
Radar is an acronym for Radio Detection and Ranging. At its simplest, an aircraft radar system consists of a transmitted radio signal aimed by an antenna in a particular direction, and a receiver that detects the echoes of any objects in the path of the signal. The transmitter consists of an electronic circuit that oscillates at a specific frequency, much higher than those used for TV or radio broadcasts. This signal is sent out in small bursts of electromagnetic energy, called pulses, through which the antenna produces a narrow beam. The distance between the target and the antenna is determined by the time it takes between transmitting the pulse and receiving the echo. Because the radar signal travels at the speed of light, which is constant, a radar system can easily determine how far away an object is and how fast it is traveling.
Air traffic control radars use a beam shaped like a fan, horizontally narrow and vertically wide, to detect high-flying aircraft. The beam scans around in a circle every two to three seconds, and displays echoes on a circular screen called a plan-position indicator. The controller can track these echoes, or “blips,” on the display to determine where the aircraft is headed. This method is called primary radar, but despite its name, is infrequently used in modern times due to the number of aircraft in the sky. Secondary radar is more popular, and features a coded pulse sequence sent to the aircraft and a transponder on the aircraft which generates a coded return, which contains information about the aircraft.
Despite its enormous utility, radar does have its limits. Aircraft flying low enough can fly beneath a radar system’s sweep, and range is a concern as well. The further out a radar system projects, the exponentially greater power requirements become for the system; to double a radar’s range, transmitted power must be boosted by a factor of sixteen. This is why typical radar systems used to track aircraft have ranges of 100 kilometers. Weather can also negatively affect long-range radar due to attenuation.
Because electromagnetic waves “bounce off” of objects that conduct electricity, aircraft made from carbon fiber composites, wood, and canvas produce very small radar echoes. Specific shapes can also deflect radar signals away from the receiver rather than towards it. Stealth aircraft like the F-117 Nighthawk and B-2 stealth bomber are designed around this principle.
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