Radar and Stealth Technology

By Blake Sharin

Outline

• Background• Radar

– How radar works– Echo and Doppler Shift– Understanding Radar

• Stealth Technology– History– How it works– Future

Who uses Radar Systems?

• Radar is used everyday– Air Traffic Control– Police– NASA– Military– Meteorologists

Echo and Doppler Shift

• Echo occurs because some of the sound waves in your shout reflect off of a surface (either the water at the bottom of the well or the canyon wall on the far side) and travel back to your ears.

• The length of time between the moment you shout and the moment that you hear the echo is determined by the distance between you and the surface that creates the echo.

Echo and Doppler Shift (Contd.)• Doppler shift occurs when sound

is generated by, or reflected off of, a moving object.

• Doppler shift in the extreme creates sonic booms.

• Let's say there is a car coming toward you at 60 miles per hour (mph) and its horn is blaring. You will hear the horn playing one "note" as the car approaches, but when the car passes you the sound of the horn will suddenly shift to a lower note. It's the same horn making the same sound the whole time. The change you hear is caused by Doppler shift.

Echo and Doppler Shift (Contd.)

• Combine Echo and Doppler shift– If you send out a loud sound toward a car

moving toward you, some of the sound waves will bounce off the car (an Echo).

– Because the car is moving toward you, the sound waves will be compressed. Therefore, the sound of the echo will have a higher pitch than the original sound you sent.

– If you measure the pitch of the echo, you can determine how fast the car is going.

Understanding Radar

• The echo of a sound can be used to determine how far away something is.

• The Doppler shift of the echo can determine how fast something is going.

• Sound radar creates what is known as sonar.– Boats and Submarines

• You could use the same principles with sound in the air, but sound in the air has a couple of problems

What are the problems? Solutions?

• Sound doesn't travel very far – About a mile at the most.

• Almost everyone can hear sounds, so a "sound radar" would definitely disturb the neighbors.

• Because the echo of the sound would be very faint, it is likely that it would be hard to detect.

• Radar therefore uses radio waves instead of sound.– Radio waves travel far, are

invisible to humans and are easy to detect even when they are faint.

How are Airplanes Measured?

• The idea is for the radar antenna to send out a burst of radio energy, which is then reflected back by any object it happens to encounter.

• The radar antenna measures the time it takes for the reflection to arrive, and with that information can tell how far away the object is.

• The metal body of an airplane is very good at reflecting radar signals, and this makes it easy to find and track airplanes with radar equipment.

Stealth Technology• The goal of stealth technology is

to make an airplane invisible to radar. There are two different ways to create invisibility:

– The airplane can be shaped so that any radar signals it reflects are reflected away from the radar equipment.

– The airplane can be covered in materials that absorb radar signals.

• Most conventional aircraft have a rounded shape. This shape makes them aerodynamic, but it also creates a very efficient radar reflector.

• The round shape means that no matter where the radar signal hits the plane, some of the signal gets reflected back

Stealth Technology (Contd.)

• A stealth aircraft, on the other hand, is made up of completely flat surfaces and very sharp edges.– When a radar signal hits a

stealth plane, the signal reflects away at an angle

• Surfaces on a stealth aircraft can be treated so they absorb radar energy.

• The overall result is that a stealth aircraft like an F-117A can have the radar signature of a small bird rather than an airplane.

Stealth Technology (Contd.)

• The only exception is when the plane banks.– There will often be a

moment when one of the panels of the plane will perfectly reflect a burst of radar energy back to the antenna.

• Is it ironic that stealth planes resemble UFO Drawings and sightings?

Future of Stealth Technology

• In the future, stealth technology will not only be incorporated in fighters and bombers but also in ships, helicopters, tanks and transport planes.

References

• http://www.lowobservables.com/

• http://people.howstuffworks.com/