Radar is an instrument to detect approaching or stationary objects and their direction. For instance, an approaching space craft or any airplane is determined by radar. The word RADAR is actually an acronym for Radio Detection and Ranging. It uses electromagnetic waves to achieve its mission. Radars were first used by ships to detect icebergs.


Brief History:



Many scientists have contributed to the development of the modern radar. However, the idea was greatly developed by a Scottish physician named Robert-Watson Watt at the time of the Second World War and radars were widely used since then.


The Basic Physics involved –Echo and Doppler Shift


Echo: The basic principle of radar is based on ‘echo’ which can be understood by a simple experiment which is often stated in any physics book.  Stand near a hill or any desolate place and let out a scream; simultaneously start a stopwatch and note down the time. The voice, after getting reflected off the surface travels back. This is the ‘echo’; note down the time of its arrival.


Doppler shift: This is also popularly known by carefully hearing the sound of a horn of a moving car. The difference perceived in the sound as it approaches and recedes is known as Doppler shift.


In the first case, by knowing the speed of sound and the time gap between screaming and the first ‘echo’, the distance between you and the hill can be calculated. In the second case, by measuring the pitch difference, the speed of the car is determined. Combing these two would lay the foundation for radar, only difference being that the above experiments used sound waves while most radars use high-energy radio waves.


Operation of a Radar


Powerful radiations of long wavelength, called radio waves are sent out from an antenna and their energy is detected after they bounces off a remote object. As radio waves move through the air at the speed of light, the distance of the object can be calculated by the time of return of the reflected electromagnetic waves. This approximate distance is known as the slant range, ‘R’, and is calculated by applying the following formula:

R=c-t/2 where c is the speed of light (3*10 8 meters per second) and t is the time taken




The direction is determined basically by the directivity of the antenna.



Primary components of the radar equipment


Transmitter: The magnetron generates  high-intensity radio waves while the antenna shoots them out in short bursts lasting for about a microsecond. The transmitter is then turned off.


Duplexer: This component switches the antenna alternatively between the transmitter and the receiver so that only one is used.


Receiver: This component has an antenna which listens to the “echo” produced by the radio waves, as a result of reflection from a remote target. The receiver then amplifies the waves and provides the video signals on the display screen.


In some radars, the transmitter antenna and the receiver antenna are the same so that the same antenna is used for transmitting as well as receiving. Also, there is a recording device in most of the radars to store the pulses for later processing.






Types and uses of Radars


♦  Aviation and Defence industry: Here, radars are used by airports to guide the planes for smooth and safe landing, by detecting the proximity of an aircraft to the earth. Radars may also be mounted on the plane to detect nearby objects. Sometimes, for aerial views, Side-Looking Air-borne Radars are used where radar antennas are mounted on aircraft to send a beam of waves to the ground at an angle perpendicular to the aircraft’s flight path. Radars are present in military aircrafts to locate the target of missiles and enemy planes. Radars also find use in police vehicles, as Doppler Radars, to track passing vehicles.


♦  Meteorological industry: Weather Radars detects and measures the amount of precipitation in the clouds. Meteorologists are thus able to predict an approaching storm, if any.


♦  Biological Research: Radars are used in tracking the migratory habits of birds and their presence in certain localities.


♦  Marine industry: Radars, more specifically sound radars or sonars that work on sound waves, are used by ships as an aid to navigation. They are also used in submarines to communicate with or perceive other vessels.


Not long from now, radars will find prominent use in space industry also.

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