Radar: A Silent Eye in the Sky

Daniel Brosk Period Two

Today\'s society relies heavily on an invention taken for granted: radar.
Just about everybody uses radar, whether they realize it or not. Tens of
thousands of lives rely on the precision and speed of radar to guide their plane
through the skies unscathed. Others just use it when they turn on the morning
news to check the weather forecast.

While radar seems to be an important part of our everyday lives, it has
not been around for long. It was not put into effect until 1935, near World War
II. The British and the Americans both worked on radar, but they did not work
together to build a single system. They each developed their own systems at the
same time. In 1935, the first radar systems are installed in Great Britain,
called the Early Warning Detection system. In 1940, Great Britain and the
United States install radar aboard fighter planes, giving them an advantage in
plane-to-plane combat as well as air-to-ground attacks.

Radar works on a relatively simple theory. It\'s one that everybody has
experienced in their lifetime. Radar works much like an echo. In an echo, a
sound is sent out in all directions. When the sound waves find an object, such
as a cliff face, they will bounce back to the source of the echo. If you count
the number of seconds from when the sound was made to when the sound was heard,
you can figure out the distance the sound had to travel. The formula is:
(S/2) X 1100 = D (Half of the total time times 1100 feet
per second equals the distance from the origin to the reflection point)

Of course, radar is a much more complicated system than just somebody
shouting and listening for the echo. In fact, modern radar listens not only for
an echo, but where the echo comes from, what direction the object is moving, its
speed, and its distance. There are two types of modern radar: continuous wave
radar, and pulse radar.

Pulse radar works like an echo. The transmitter sends out short bursts
of radio waves. It then shuts off, and the receiver listens for the echoes.
Echoes from pulse radar can tell the distance and direction of the object
creating the echo. This is the most common form of radar, and it is the one
that is used the most in airports around the world today.

Continuous wave radar works on a different theory, the Doppler Theory.
The Doppler Theory works on the principle that when a radio wave of a set
frequency hits a moving object, the frequency of the wave will change according
to how the object is moving. If the object is moving toward the Doppler radar
station, the object will reflect back a higher frequency wave, If it is moving
away, the frequency of the wave will be lower. From the change in frequency,
the speed of the target can This is the type of radar that is used to track
storms, and the type of radar used by policemen in radar guns.

These are the basics of radar. But, there is a lot of machinery and
computer technology involved in making an accurate picture of what is in the sky,
on the sea, or on the road. Most radar systems are a combination of seven
components (See Appendix A). Each component is a critical part of the radar
system.

The oscillator creates the actual electric waves. It then sends the
radio waves to the modulator.

The modulator is a part of the timing system of a radar system. The
modulator turns on and off the transmitter, creating the pulse radar effect. It
tells the transmitter to send out a pulse, then wait for four milliseconds.

The transmitter amplifies the low-power waves from the oscillator into
high-power waves. These high-power waves usually last for one-millionth of a
second.

The antenna broadcasts the radar signals and then listens for the echoes.


The duplexer is a device that permits the antenna to be both a sending
device, and a receiving device. It routes the signal from the transmitter to
the antenna, and then routes the echoes from the objects to the receiver.

The receiver amplifies the weak signals reflected back to the antenna.
It also filters out background noise that the antenna picks up, sending only the
correct frequencies to the signal processor.

The signal processor takes the signals from the receivers, and removes
signals from stationary objects, such as trees, skyscrapers, or mountains.
Today, this is mostly done by computers.

And last, but not least, we come to