What Is Radar The word “radar” was invented by scientists of the United States Navy during World War II. The word comes from the first letters in the term “radio detection and ranging.””Detection,” as used here, means finding an object or target by sending out a radio signal that will bounce back off the target as a radio echo. “Ranging” means measuring the distance to the target from the radar set(the device tat sends out the radio signal and picks up the returning echo). Radar set on the ground uses radio echoes to locate aircraft, ships, and other objects. Radar sets can locate artificial satellites and spacecraft thousands of kilometres from the earth.
They can find such “targets” even in darkness, smoke, clouds, fog, or rain. Radar is also used in weather prediction to locate storm systems.An airplane can carry a radar setet to aid in determining the airplane’s ground speed.
Ships can carry radar to detect icebergs, other ships, and aircraft. Radar can do more than find a target. It can tell how fast and in which direction the target is moving. This information can be used to direct the firing of guns and missiles to protect a country against attack.In peacetime, radar can help navigate ships, land planes in a fog, and guide astronauts.
Radar can help control street traffic and assist the police in finding speeding automobiles. Radar sets come in many sizes. A small set, made for use in a guided missile, is not much larger than a coffeepot.
The larger sets used to study distant planets may oupy a building many stories high.The size of a radar set depends on the job it is expected to do. But all radar sets, regardless of their size, use the principle of the echo. How Radar Works Radar sets produce radio signals.
They radiate(send out) these signals into space with a transmitter. When a radio signal strikes an object such as an airplane, part of the signal is reflected back to the radar antenna.The signal is picked up there as a radar echo. A radar set changes the radar echo into an image that can be seen on a screen. A radar set also gives the direction of the target and its distance from the set.
How Radar Began In 1900 a radio pioneer, Nikola Tesla, noticed that large objects can produce reflected radio signals that are strong enough to be picked up. He knew that reflected radio signals are really radio echoes.So he predicted that such echoes could be used to find the position and course of ships at sea. But nothing was dine about it until just before World War II. In 1935, Robert A. Watson)Watt and other British scientists developed a system of radio echoes that could detect approaching aircraft. This later developed into the radar system that proved effective against German air raids on Britain in World War II.
An important step in making radar possible had taken place in the United States in 1925.The new idea was to send out the radio signals in short bursts, called Pulses. This was so important because if you imagine that you are about to shout across a canyon to make an echo.
If you shout a long sentence, the first words will come back before you can finish the last words. It would be impossible to hear the echo clearly because it would be mixed with your own speech. But suppose you shout a short word, such as “Hello” The echo comes back crisp and clear with no interference.
Now suppose a radio signal is given off in a short burst, or pulse, and is reflected from an object. The echo comes back clearly.But if the radio signal lasts a long time, the echo comes back while the signal is still going out. The radar operator cannot detect the echo at all. By using echoes, you can find out how far away the reflecting wall of a canyon is. Sound travels through the air at a speed of about 335 meters (1,100 feet) a second.
If the sound takes 1 second to hit the canyon wall and return, it must have gone 335 meters.But that is the distance of the round trip the wall and back. The wall must be half that far away, or 167.5 meters(550 feet). To find the distance to an echo)making surface, count the seconds it takes for the echo to return. The multiply the number of seconds by 167.5 meters.
A radar set works on the same principle.It sends out a very short radio signal. Then it counts the time it takes for the echo to cone back. Radio signals travel at a known speed which is 300,000 kilometres (186,000 miles) a second (the speed of light).
If the radio signal comes back in 1/1000 second, then the round trip is 300 kilometres (186 miles). The target must be half that far, or 150 kilometres (93 miles), away.The location of the target in relation to the radar is found in a different way. The radar antenna sends ut radio pulses in a narrow beam, much like the beam of a flashlight.
The antenna (and its beam) is slowly rotated through all possible directions, searching the entire sky for targets. An echo comes back, to strike the plane. When an echo comes back, it can be seen on a screen.This shows the radar operator where the radar beam hit the plane and ,therefore, the location of the plane. Between 1935 and 1939, a network of radar stations was built along the coast of Britain.
These radar sets gave early warning of attacking planes an missiles. Germany had also developed radar ground stations before the beginning of World War II. The United States developed radar systems during the war and later created both early) warning (DEW) lines of radar extending the coverage of radar detection system. Later developments included the ballistic)missile)early warning system(BMEWS) and the combining of radar equipment with high)speed digital computers.Radar Systems A radar set, also called a radar system, has four main parts)a transmitter, and antenna, a receiver, and a indicator. The transmitter produces the short radio pulses. Each pulse lasts only about 1/1,000,000 second.
There are usually about 200 or 300 pulses produced each second. The same antenna is used both to send out the radio pulses and to pick up the echoes.The returning echoes are sent to the receiver, where their strength is increased. The echoes then go to the indicator, which shows the range and direction of the target to the operator. On the indicator the echoes appear …