Alex Webster
Writ 340
5/2/14
Radar: Turning Echoes into Info
Abstract: Radar, or radio detection and ranging, uses the reflection of radio waves to determine
the position and speed of objects. The radar sends out radio waves and measures how long it
takes for them to return, allowing the radar to determine the objects position. Change in
frequency caused by the Doppler effect can also be measured, allowing the speed of the object to
be determined. Radar was originally created for military purposes such as detecting enemy
aircraft. Later it was applied to other technologies such as guided missiles. In modern times, the
application of radar has extended well beyond the military and into civilian use. Weatherman,
policemen, NASA, car manufacturers, and more, all make use of radar. Radar may not be visible
in everyday life, but its effects are felt every day.
A captain is informed by his crew that something is approaching, and approaching fast!
He turns to look at the crew member and sees him pointing at a screen with a bright green line
moving around in circles. As it rotates, green dots
appear and then gradually fade away on the screen.
The dots move closer and closer to the center of the
screen until finally the captain actually sees planes
flying above, moving in on their position. But how did
the crew member know they were even out there in the
Figure 1: Radar display comonly found in modern
military ships and planes [2].
first place? What was making the dots show up on the
screen? The answer is radar, and it is one of the most useful technologies the military has ever
created.
Why It Was Created
Radar, which is actually an acronym (see Figure 2), is a method of using the reflection of
radio waves to determine the location and speed of objects at a distance. Radar was first
Webster 2
discovered at the beginning of the 20th century [4]. As early as 1922, US Naval officers had
discovered electromagnetic energy could be used to find ships, even in heavy fog where vision
was limited [4]. Prior to WWII, the British began
searching for ways to further utilize
electromagnetic energy. British physicist Robert
Watson-Watt was tasked with using
electromagnetic waves to build a “death ray” to
destroy enemy aircraft. While the death ray was
unsuccessful, Watson-Watt did discover radio waves could easily detect aircraft. His work led to
the creation of the first full scale, practical radar system and led to the establishment of the
“Chain Home” system of radar stations in Britain [9].
These systems proved invaluable to the British during the war. In particular, during the
Battle of Britain in the summer of 1940, British radar was able to locate and track the German
Luftwaffe planes. This gave the British Royal Air Force the upper hand, allowing them to stop
the Germans from invading Great Britain [9]. Radar gave the Allies a great advantage over their
enemies and would continue to be developed by the military for use in the detection of objects.
Soon the civilian world would begin adopting radar and applying it to everything from ships, to
aircraft, to roads. Radar has remained as one of the most reliable ways to track and determine the
positioning of objects. As technology has developed throughout the years, the use of radar has
developed as well. Since World War II radar has been adapted for use in astronomy,
meteorology, motor vehicle safety, and more. Today radar continues to be an incredibly
important piece of technology.
Webster 3
How It Works
Radar makes use of radio waves to locate objects. Radio waves are found on the
electromagnetic spectrum of radiation. Electromagnetic radiation is a form of energy that moves
through space as waves. The electromagnetic
spectrum (See Figure 4) is the range of
frequencies over which electromagnetic radiation
exists and includes infrared, ultraviolet, and even
visible waves [6]. Radio waves have the largest
wavelength on the spectrum. While visible light
Figure 3: Basic characteristics of an electromagnetic wave.
Frequency is the number of peaks per unit of time.
has wavelengths from 300 – 700 nanometers, radio waves have wavelengths from 1 millimeter to
100 kilometers [10]. What makes radio waves so special is that they are completely invisible,
harmless, can travel long distances, and carry a lot of energy, which makes them easy to detect
[3]. These are the same reasons radio waves are used in transmitting music to, well, your radio.
Whereas your radio is looking to pick up incoming radio waves, radar systems receive their own.
Figure 4: The electromagnetic spectrum. Each type is characterized by its wavelength and frequency [5].
Webster 4
Radar is able to locate and track objects by observing the reflection of radio waves [13].
When radio waves are sent out, they travel in a straight line until coming into contact with an
object, such as a boat or plane. When the radio wave makes contact with the object, the wave is
scattered, with some of its energy being reflected back towards the source. This works in the
same way an echo does. The sound waves travel out, reflect off a wall, and come back, allowing
you to hear your own voice. In the same way you are able to hear your voice after it is reflected,
radar systems are able to observe the reflected energy. The radar calculates how long it took the
wave to return and, using the speed of the wave, is able to calculate the distance the object is
away from the radar [13]. Radio waves travel at about the speed of light, or 186,000 miles per
second. This means it only takes 10.7 microseconds, or about a millionth of a second, for the
radar to send out and receive the signal [13]. This is one way in which radar calculates position.
But how can we determine how fast the object is moving?
The easiest method for calculating speed is done by looking at the position of the object
being measured at varying times. A radio wave is sent out and the position of the object being
observed is recorded. At a set time later, another wave is sent out and the position is marked
again. The radar system then calculates the distance moved by the object and divides it by how
long it was in between the signals [14]. This allows the radar to give the average speed of the
object on the screen.
Anyone can use this method to calculate speed. Say you are on a road trip. If it took you
6 hours to travel from Los Angeles to San Francisco (about 380 miles), you could easily
calculate that you traveled at an average speed of about 63 miles per hour. Radar does this as
well, just much quicker and many more times. However, this method has its limitations. If there
are numerous objects on the screen at once, it can be difficult to track which signal belongs to
Webster 5
which. In addition, if the measurement devices on the radar are not powerful enough, they can
only give broad estimates for the speed. Increasing the power of the measurement devices means
a much more expensive radar system. In order to avoid high costs or inaccurate speed
measurements, a different technique is used.
The second method radars use to determine speed is by using the Doppler effect. You
may have noticed the Doppler effect every day and not realized it. The Doppler effect describes
the change in the pitch of a sound coming from a moving source. For instance, you might hear a
police siren coming down the road towards you. As the police car passes you, however, you
notice the siren suddenly changes and sounds much deeper than before. This is the Doppler
effect in action.
The Doppler effect happens because as the source moves towards you, each sound wave
being produced starts at a position closer
to you than the last one. Therefore, each
wave takes a bit less time to reach you
than the last one. This makes it appear
that the frequency of the waves is higher
than it actually is, as more waves reach
Figure 5: Depiction of the Doppler effect [3].
you in a shorter time. The opposite
happens as the source moves away. Each wave takes longer to reach you than the previous,
causing an apparent decrease in the frequency of the wave [3]. This shifting frequency causes the
observed change in sound as the siren passes by. As the police car moves towards you, the sound
waves from the siren are being compressed. As the car moves away, the sound waves are being
pulled apart.
Webster 6
So why is this useful to radar? When radio waves bounce off an object in the distance, the
movement of the object causes the Doppler effect to occur on the radio waves [3]. If the object is
moving towards the radar, the radio waves are compressed and the returning radio waves have a
higher frequency. Special instruments built into the radar can determine these frequencies and
use them to calculate how fast the object was moving towards or away from the radar. Now that
we understand how radar calculates position and speed, let us look at how it is used.
How The Military Uses It
Radar was originally developed during WWII to detect aircraft and the military has
continued to use it with great success. Most military ships, planes, and bases are equipped with
radar systems [3]. This allows the military to detect everything from enemy ships, to planes, to
submarines, to incoming missiles from miles and miles away. Radar is still the best method the
military has for detecting threats. That is not the end of radars uses however. One of the most
important applications of radar is in tracking systems.
The use of radar in tracking systems led to the creation of the guided missile. Radar can
quickly detect targets and give information on their position and speed. A small scale radar
system can be placed inside of a
missile. This allows the missile to
analyze its target in mid-flight. After a
Figure 6: Radar guided missile make use of the high speed of radio wave
reflection to detect targets and adjust its path.
radar guided missile is launched, it
begins sending out radio waves, learning the position and movement of its target. The missile
then uses onboard computers to adjust its own flight based on where the target is heading. This
Webster 7
allows the missile to guide itself to the target without needing any assistance from the pilot [7].
The radar guided missile is referred to as a fire and forget missile. Pilots do not have to do any
work after they launch the missile, the radar does all the work for them!
Radar is not a fool proof system for the military, however. Modern advances have limited
the usefulness of radar to the military. Modern stealth planes such as the Lockheed F-117
Nighthawk are designed with strange angles, lines,
and edges. This odd shape deflects radio waves
away from the radar instead of back at it, keeping
the radar from picking up the reflected waves [7].
When being followed by a missile, planes release
metallic strips known as chaff. The chaff reflects
Figure 7: Modern stealth planes are nearly invisible on
radar [1].
lots of radio waves instead of just a few, making the missile believe there are many targets
instead of just one [7]. Radar jammers have been created that send the same frequency radio
wave signal at an enemy radar. This causes the radar to believe waves are being reflected back
from everywhere, all the time, stopping it from making any calculations [7]. These systems
provide valuable defense for military aircraft and can save lives. However, these anti-radar
technologies limit the usefulness of radar as an offensive tool for the military.
Radar will continue to prove indispensable as a detection tool for the military. However,
its usefulness as an offensive tool is diminishing. Radar systems are beginning to be replaced by
new systems, such as lasers. While this is true, it is not the end of the story for radar. Radar has
been successfully adopted by civilians as well.
Webster 8
How Everyone Else Uses It
While the military was adapting radar for use in weapons, civilians were finding
innovative uses for radar in every field imaginable. Cops for example make great use of the
Doppler effect by determining who to give tickets to with their radar guns [3]. Like the military,
air traffic controllers use radar to monitor aircraft as they approach airports. Commercial aircraft
even have systems that detect the incoming radio
waves and send back specialized signals that state
their identification code and altitude [10]. NASA uses
radar to detect asteroids and satellites, and to study the
far reaches of space. They also use it to map the
terrain of planets, including Earth itself [3].
Meteorologists use radio waves of a different length
Figure 8: Meteorologists are able to track hurricanes
using radar [8].
than other radar systems. These special radars use
radio waves that reflect off from water instead of metal. This allows storm systems to be tracked
and levels of precipitation to be measured [3].
While these innovations have proven invaluable to the modern world, the future of radar
is just as promising. Scientists are currently looking at ways to use radar to detect weapons
concealed by people, making airport security a breeze [12]. Cars are beginning to use radar to
detect fast approaching objects and avoid collisions. Radar allows cars to detect the speed and
position of vehicles around them. Just as the self-guided missile uses this information to follow
targets, cars can use this information to adjust its path by automatically braking, accelerating,
and steering. This allows cars to brake to avoid collisions and maintain safe spacing from
Webster 9
vehicles next to them. Self-driving cars could become common sooner than you think and radar
makes them possible [11].
Radar began by helping the Allies win WWII and continues to live up to those lofty
expectations every day. Perhaps most importantly though, radar makes the door at the grocery
store open when you walk up [3]. And who doesn’t love that?
Biography
Alex Webster is currently a junior studying mechanical engineering at the University of Southern
California. He hopes to acquire a master’s degree in mechanical engineering before entering the
defense industry.
Alex Webster
(619) 756-0498
awwebste@usc.edu
Webster 10
Bibliography
[1] Allmon II, Staff Sgt. Aaron. F-117 Nighthawk. Digital image. Wikipedia. N.p., 6 Aug. 2002.
Web. 11 Mar. 2014. <http://en.wikipedia.org/wiki/File:F-117_Nighthawk_Front.jpg>.
[2] Baba, Toshinori. Radar Display. Digital image. Wikipedia. N.p., 13 June 2009. Web. 11 Mar.
2014. <http://en.wikipedia.org/wiki/File:Yokosuka_02.JPG>.
[3] Brian, Marshall. "How Radar Works." HowStuffWorks. HowStuffWorks.com, 01 Apr. 2000.
Web. 18 Feb. 2014. <http://science.howstuffworks.com/radar.htm>.
[4] Browne, J. Celebrating Radar Technology. 50 Vol. NEW YORK: Penton Business Media,
Inc. and Penton Media Inc, 2011. Print.
[5] The Electromagnetic Spectrum. Digital image. Growblu. N.p., n.d. Web. 11 Mar. 2014.
<http://growblu.com/research-and-development/measuring-light>.
[6] “Electromagnetic Spectrum.” The Penguin Dictionary of Science. Penguin, 2009. Print.
[7] Electronic Warfare. 6 Vol. New York: McGraw-Hill, 2007. Print.
[8] Hurricane Frances. Digital image. NOAA. N.p., 9 May 2004. Web. 11 Mar. 2014.
<http://www.noaanews.noaa.gov/stories2004/s2311.htm>.
[9] Radar. ABC-CLIO, 2005. Print.
[10] “Radar.” The Penguin Dictionary of Science. Penguin, 2009. Print.
[11] Richard, Russell. "HOW IT WORKS: Radar, Laser Systems Compete." The Globe and Mail
(1936-Current): G12. 2007. Print.
[12] Sarabandi, Kamal. "A New Use For Weapons-Detecting Radar System." Tech Briefs TV.
Remcom, 08 Apr. 2013. Web. 13 Feb. 2014. <http://video.techbriefs.com/video/Weaponsdetecting-radars-Mconne>.
[13] Schneider, E. G. "Radar." Proceedings of the IEEE 84.12 (1996): 1775-827. Print.
[14] “Speed.” The Penguin Dictionary of Science. Penguin, 2009. Print.