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How does Radar Work?

Police officers use radar to determine the speed of passing vehicles.
England developed radar in the late 1930s and used the system to detect German planes during World War II.
Radar is an acroynm for Radio Detection And Ranging.
Radar uses radio waves, which have the highest frequency on the electromagnetic spectrum.
Radio telescopes record changes in the radar waves they have bounced off of distant objects, such as the planet Mars, to gain data on their targets.
A warship's radar unit can be rotated to track an individual target or sweep over a broad area.
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  • Written By: Michael Pollick
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  • Last Modified Date: 22 August 2014
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The concept of using radio waves to detect objects goes back as far as 1902, but the practical system people know as radar began in the late 1930s. British inventors, aided by research from other countries, developed a rudimentary warning system that could detect objects moving towards the coastline of England. The system used high-frequency radio waves to detect German planes and calculate their distance. This purpose lead to the term, which is actually an acronym for RAdio Detection And Ranging.

The principle behind this technology may sound confusing at first, but a simple experiment can demonstrate the basics. A person with a very accurate stopwatch and super hearing is facing the side of a mountain somewhere in the distance. She holds the stopwatch in one hand and starts timing as she screams as loudly as she can towards the mountain. When the first echo of her voice can be heard, she stops timing. She has now become a basic radar unit — since she knows how fast sound travels, she can calculate the distance between herself and the mountain by using the elapsed time on the stopwatch.

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Radar works on many of the same principles demonstrated in this experiment. Instead of one person screaming, a powerful radio beam is sent out at a specific frequency. When this burst of radio energy strikes a solid object, at least part of that energy will be reflected back to the transmitter. This signal may not be very strong, but a sensitive electronic receiver can amplify it. The transmitter and receiver are usually mounted close together, much like a person's mouth and ears.

By calculating the speed of the radio waves and the time it takes for the signal to bounce off the object and hit the receiver, a radar operator can gauge the distance between himself and the object. Moving the transmitter to different points allows the operator to receive multiple returns. All of these individual reflections are combined to estimate the size of the object or objects being struck.

The technology has improved considerably since the days of World War II, but the underlying principles are still the same. Calculations about an object's speed and direction are made from the results of transmitter and receiver data. When a radar antenna is seen spinning in place, it is sending out thousands of signals and receiving them just as quickly.

The radio frequencies on modern systems are now largely in the microwave range, unlike the shortwave radio frequencies used by the British inventors. Radar jammers use matching frequencies to confuse the receivers looking for authentic ones, but microwave frequencies are much more difficult to jam.

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anon963294
Post 7

@repoman: Radars use either a moving target receiver or the doppler effect to filter out stable objects. A moving target receiver uses an in phase signal and and a out of phase signal.

If the receiver determines the phase shift for both is 0 then the target is considered stationary and is dropped from the final product. A doppler receiver uses the change in frequency (i.e., doppler shift) to determine if the target is stationary or not.

anon307744
Post 6

If we use ultrasonic waves instead, what will happen?

anon226409
Post 4

One reason that solid or stable objects may not appear on a radar screen is the degree of tilt of the radar dish. A typical weather radar dish rotates 360 degrees in a protective dome, and the operator can select how high in the sky the readings should be. This can mean thousands of feet if the meteorologist is looking at the tops of storm clouds. Unless the building is 500 stories high, the radar waves aren't going to bounce off it and return to the receiver.

If the operator tilted the radar dish to nearly ground level, however, a lot of houses and other solid objects would show up on the screen. As it stands, some radar screens do show stable objects close to the physical radar station. Meteorologists usually refer to this indistinct blob as "ground clutter".

repoman
Post 3

Why are homes and stable objects not shown on a radar? Can anyone please help me with this question as soon as possible.

anon37401
Post 2

It is more difficult to jam microwave frequencies than radio wave frequencies because microwaves are smaller, meaning they can have more frequencies. The more frequencies there are, the more that must be jammed.

petal
Post 1

Why is it more difficult to jam microwave frequencies than radio wave frequencies in case of a radar?

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