PRESENTATIONPRESENTATION

CONTEMPORARAY STUDENTS

NAME: AZIZ ZOAIB & NOMAN SARWER

ID: FA06-BS-0013 & FA06-BW-0005

COURSE: LST (LINEAR SYSTEM THEORY)

TOPIC: RADARS AND DOPPLER EFFECT

ABOUT RADAR

Radar (radio detection and ranging) is an electronic system

for transmitting electromagnetic signals and receiving echoes

from objects of interest (targets).

Most radars work by transmitting a pulse of electromagnetic

energy at a target and then listening with a receiver for the

reflected echo from the target. Since electromagnetic waves

travel at the velocity of light [186,411 miles (300,000

kilometers) per second]

CONTD

The time delay between the transmitted pulse and the received echo can be used to determine the distance to thetarget (distance = speed × time).

Radar is standalone system active system having its own transmitter, receiver, antenna, processor etc.

In radar strong radio waves are transmitted and receiver listens for scattered echoes very weak but can be amplified easily.

SIMPLE RADAR DIAGRAM

RADAR FUNCTIONS

TRANSMITTER:• Generate radio waves• Perform modulation• Amplification to high power

RECIEVER:• High sensitivity• Very low noise• Ability to discern a received signal from background noise

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PROCESSING & CONTROL:It regulates the rate at which pulses are sent (PRF). Synchronizes the

function between Transmitter, Receiver, display, duplexer etc.

DUPLEXER:A switch to alternatively connect Tx and Rx to antenna. Protects

receiver from high power of transmitter during transmission it aligns to

transmitter. After pulse has been sent, it aligns antenna to receiver.

CONTD

ANTENNA:Takes radar pulses from transmitter and puts into the air. Focuses energy

into the well designed beam. Antenna is of two types

1) Physically moving

2) Electronically steered

DISPLAY:Presents received information to the operator. It is of two types

1) PPI (Plan Position Indicator)

2) A-scope or A-scan

PPI IMAGE

SOME HISTORY

1886-88: Hertz demonstrated the Generation, reception and

scattering of e.m waves.

1903-04: Hulsmeyer developed and patented a primitive form for

ships collision avoidance radar for ships.

1925: Beginning of Pulsed Radars.

1937: CHAIN HOME RADAR SYSTEM in Britain designed by

Prof Watson Watt.

1941: US, FM band Early Warning Radar at Oahu made.

RADAR TYPES

Detection and search radars

Missile guidance systems

Battlefield and reconnaissance radar

Air Traffic Control and navigation

Space and range instrumentation radar systems

Weather-sensing Radar systems

Radars for biological research

MAIN TYPES OF RADAR

There are two main types of radar:

1)Primary Radar

Continuous wave Radar Pulse Radar

2)Secondary Radar

PRIMARY RADARS

1)CONTINUOS WAVE RADAR:Continuous-wave radar system is a radar system where a known stable

frequency continuous wave radio energy is transmitted and then received from any reflecting objects. The return frequencies are shifted away from the transmitted frequency based on the Doppler effect if they are moving.

The main advantage of the CW radars is that they are not pulsed and

simple to manufacture.

CW radars also have a disadvantage because they cannot measure range. Range is normally measured by timing the delay between a pulse being sent and received, but as CW radars are always broadcasting, there is no delay to measure.

PRIMARY RADARS

2)PULSE RADAR: The PULSE radar is the more conventional radar, which transmits a burst

of radar energy and then waits for the energy (or echo) to be reflected back to the antenna. After a specific period of time (depending on how far the radar is searching) another pulse will be sent followed by another listening period. Since radar waves travel at the speed of light, range from the return can be calculated.

BASIC PULSE RADAR TERMS: Pulse Duration Pulse Repetition Time Pulse Repetition Frequency Listening Time

BASIC RADAR TERMS

1)PULSE DURATION: The time a radar set is transmitting radio frequency (RF) energy. It is also

referred to as pulse width (PW). Pulse duration is measured in millionths of a second or microseconds (usec).

2)PULSE REPETITON TIME: This is the time required to complete one transmission cycle. It is the time

from the beginning of one radar pulse to the beginning of the next. It is the reciprocal of our next term, Pulse Recurrence Frequency (PRF).   This term represents the period for one transmission cycle.

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3)PULSE REPETITON FREQUENCY: The PRF equals the number of pulses per second the radar transmits. If

you want the radar to look at long ranges, a low PRF is required (this allows time for the radar energy to be reflected by the target and to return to the antenna before the next pulse is transmitted). For shorter ranges, a higher PRF can be used.

4)LISTENING TIME:

Listening time is the part of the Rest Time that the radar can receive and process the echoes of radar returns. It is measured is usec.

SYNTHETIC APERTURE RADAR(SAR)

The SAR mode of the APG-70 provides the Strike Eagle aircrews with a capability unmatched by any other fighter. SAR technology provides a resolution (or the ability to see closely spaced objects clearly as opposed to one large return) over 100 times greater than a conventional radar.

SAR technology starts with the antenna. The larger the antenna -- the better the resolution. Since fighters are limited in size, one way around this is to have the radar take several "snapshots" of an area on the ground. This simulates a much larger antenna (it also requires a high powered computer). Since the F-15E is flying at around 9 miles per minute, the range and azimuth to the target constantly changes. Range is calculated conventionally (addressed above). The azimuth is measured by the Doppler Shift. By taking the Doppler shifts from numerous radar returns of the same area, the computer is able to provide the phenomenal resolution required for a near photo quality presentation.

SAR

Photo of Airfield SAR Image of Airfield

DOPPLER EFFECT

The Doppler effect, named after Christian Doppler, is the change

in frequency and wavelength of a wave for an observer moving

relative to the source of the waves. It is commonly heard when a

vehicle sounding a siren approaches, passes and recedes from an

observer.

CONTD

• Waves from siren are compressed towards the observer.• Intervals between waves diminish frequency increases. • Waves from siren are stretched when siren moves away from

the observer, wavelength increases frequency decreases.

Thus this change in Frequency tells us that the source is coming

closer or separating.

Rate of change of frequency could be used to determine the

speed.

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Change in frequency is called Doppler shift in frequency and

change in wavelength is called Doppler shift in wavelength.

If frequency increases than the transmitted frequency than the

target is approaching and if the frequency decreases than the

transmitted frequency than the target is receding.

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The radiation emitted by an object moving toward an observer is

squeezed; its frequency appears to increase and is therefore said

to be blueshifted. In contrast, the radiation emitted by an object

moving away is stretched or redshifted.

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STATIONARY RADAR & STATIONARY TARGET:

If the radar and target both are stationary than than Doppler shift

is measured by td=2R/C or R=C.td/2

STATIONARY RADAR & MOVING TARGET:

If the radar is stationary and target is moving then the doppler

shift in frequency is given by fd= 2V/C.f

DOPPLER EFFECT IN OTHER APPLICATIONS

• Doppler Radar uses the Doppler effect for electromagnetic waves to predict the weather.

• The Doppler shift for light is used to help astronomers discover new planets and binary stars.

• Echocardiography - a medical test using ultrasound and Doppler techniques to visualize the structure of the heart.

NAV/AIDS

The RADAR is basically used only for location and detection. But when the aircraft is in air so we need to define routes for that aircraft. Navigation Equipments is used for this purposes.

Some Equipments of NAV/AIDS at CAA (Civil Aviation Authority)

DME (DISTANE MEASURING EQUIPMENT NDB (NON-DIRECTIONAL BEACON) ILS (INSTRUMENT LANNDING SYSTEM)

1) GLIDE SCOPE

2) LOCALIZER

CAA (Civil Aviation Authority)

The CAA has installed 9 radars throughout the country at: 1) Karachi (both primary and secondary) 2) Lahore (both primary and secondary) 3) Islamabad (both primary and secondary) 4) Rojhan (secondary radar) 5) Lakpass (secondary radar) 6) Pasni (secondary radar)

Q/A .?