Чтение общенаучной литературы. Кытманова О.А. - 36 стр.

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37
Pioneers of Radar
From the early days of radio, scientists knew that very short radio waves could be
reflected from solid objects. Heinrich Hertz, who discovered how to generate radio
waves, was aware of this. Guglielmo Marconi, the pioneer of radio on whom there
is a separate article, outlined a system like modern radar in 1922 but did no
practical work on it. In 1925, the American scientists Gregory Breit and Merle
Tuve began a series of experiments to find the height of the reflective part of the
atmosphere, called the ionosphere, and used a technique later used widely in radar.
However, it was the threat of war in the 1930s that gave a big boost to the
development of radar.
In 1935 the British government asked the scientist R. A. (later Sir Robert)
Watson-Watt to look into the possibility of a "death ray" using radio waves. He
told them such a ray was impossible but instead suggested that radio waves might
be used to detect aircraft long before they could be seen or heard. A practical
demonstration followed. On 26 February 1935, Watson-Watt succeeded in
detecting a bomber aircraft using radio waves.
The ability to give early warning of enemy air raids was so important that
Watson-Watt's ideas were quickly adopted. By the time World War II started in
1939, some 40 secret radar stations had been built around the south and east coasts
of England.
They were called "RDF" (standing for "radio direction finding") stations. While
the British were in the lead, both the United States and Germany were also
developing radar systems. In 1940, the public were told something of the secret,
and newspapers called the new system "radiolocation". However, in 1942, Britain
officially adopted the American word "radar" which stands for "Radio Detection
And flanging". By this time the radar principle had been.
The radar screen on a vessel carrying the radar antenna shown in the top diagram
indicates the location and distance of the shore, an island, and a ship The indicator,
or trace, sweeps the screen as the radar antenna rotates
extended to a number of other purposes besides aircraft and ship detection. Guns
were being armed by radar and radar was also fitted to night fighters to help them
find and attack enemy bombers. Radar-aimed bombing de-\ ices were also
developed.
So radar was first developed for wartime use. Since the 1940s, however, radar
hay come to play an important part in navigation, both at sea and in the air. How
do these different radars work?
How a Simple Radar Works
A simple radar system, as found on many merchant ships, has three main parts.
These are the antenna unit (scanner), the transmitter/receiver or "transceiver" and
the visual display unit.
The antenna is about 2 or 3 meters (7 or 10 feet) wide and focuses pulses of
microwave radio energy into a narrow vertical beam. The frequency of the radio
waves is usually about 10,000 MHz (that is 10,000 million, or 10 billion, cycles
per second! - equal to a wavelength of 3 centimeters (just over 1 inch). The
antenna is rotated (turned round) at a speed of from 10 to 25 revolutions per minute

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