Radar Lecture 1.ppt in Telecomunication engineering

what is radar and how it is working
Radar, which stands for Radio Detection and Ranging, is a system that uses radio waves to determine the distance, direction, and radial velocity of objects relative to a site. Radar works by transmitting radio waves into the air and measuring the time it takes for the waves to bounce back after reflecting off an object.

1. Radar and Navigation Systems
Lecture 1

2. Learning Objectives
•Know the application of radar system
•Comprehend basic operation of a simple pulse radar system
•Know the following terms: pulse width, pulse repetition frequency,
carrier frequency, peak power, average power, and duty cycle
•Know the block diagram of a simple pulse radar system

3. Radar: Acronym for Radio Detection and Ranging
Radar is a remote sensing technique: Capable of gathering information
about objects located at remote distances from the sensing device.
Two distinguishing characteristics:
1.Employs EM waves that fall into
the microwave portion of the
electromagnetic spectrum
(1 mm < < 75 cm)
2.Active technique: radiation is
emitted by radar – radiation
scattered by objects is detected
by radar.

4. Why microwaves?
Microwaves can penetrate haze, fog and snow readily, and rain and hail
less readily, so radar can “see through” these conditions.
An elementary radar system

5. Two Basic Radar Types
•Pulse Transmission
Continuous WaveContinuous Wave

6. Classification of radar systems

7. Radar Frequencies

8. Applications of Radar
•Air Traffic control
•Aircraft navigation
•Ship safety
•Remote Sensing
•Law enforcement
•Military

9. What does a conventional radar measure?
1. Distance to an object or collection of objects
Determined by the time it takes energy to travel to the objects
and return at the speed of light.
2
tc
r


2. Azimuth and elevation angle to the object(s)
Determined by the pointing angles of the antenna.
3. Physical properties of the object(s)
Determined by the magnitude of the backscattered power.
r = 1 km t = 6.67 s
r = 100 km t = 0.667 ms

10. Pulse duration (s) and pulse length (h, meters)
Pulse repetition period (msec) and pulse repetition frequency (s
-1
)
Duty Cycle (= T
r)
Meteorological radars send out pulses of energy with relatively long
periods of “listening” between pulses. Pulses are required, rather
than continuous waves, to determine the distance to the target.

11. Second Trip Echo: an echo from a pulse that is not the most recent pulse

12. Pulse repetition frequency (PRF): The frequency that pulses are
transmitted, measured in hertz (s
-1
)
Pulse repetition period (T
r
): The time between pulses (typical
value 1 ms)
Maximum Unambiguous Range (r
max
): The maximum distance that an object can
be located such that a pulse arriving at the object can return to the radar before
another pulse is emitted.
Definitions
)(22
max
PRF
ccT
r
r


13. Pulse Transmission
•Pulse Width (PW)
•Length or duration of a given pulse
•Pulse Repetition Frequency (PRF)
•Frequency at which consecutive pulse are transmitted
•Pulse Repetition Time (PRT=1/PRF)
•Time from beginning of one pulse to the next
•Inverse of PRF
•PW determines radar’s
•Minimum detection range
•Maximum detection range
•PRF determines radar’s
•Maximum detection range

15. Radar- RAdio Detection
And Ranging
Transmits microwaves
Elevation position, ∅
Azimuth Position, Ѳ
National Weather Service

16. Pulse Diagram
PRTPRT
PWPW
““Listening”Listening”
TimeTime
PRT=1/PRFPRT=1/PRF
Carrier Freq.

17. hello
Compare to: Acoustic Echo-location

18. hello
Acoustic Echo-location

19. hello
distance
Acoustic Echo-location

20. Hi !!
Hi !!
time
t = 2 x range / speed of sound
Example: range = 150 m
Speed of sound ≈ 340 meters/second
t = 2 X 150 / 340 ≈ 1 second

21. RADAR Echolocation
(RADAR ~ RAdio Detection And Ranging)
“Microwave Echo-Location”
Microwave
Transmitter
Receiver
Tx
Rx

22. Target Range
time
t = 2 x range / speed of light
measure t, then determine Range
Example: t = .001 sec
Speed of light = c = 3x10
8
meters/second
Range = .001 x 3x10
8
/ 2 = 150,000 m = 150 km
Tx
Rx

23. Range ambiguity
The radar time is set to zero each time a pulse is transmitted
If echo signals from the first pulse arrive after the second pulse
transmission, ambiguity arises
Maximum unambiguous range

24. Pulse Radar Components
SynchronizerSynchronizer TransmitterTransmitter
Display UnitDisplay Unit ReceiverReceiver
PowerPower
SupplySupply
ANT.ANT.DuplexerDuplexer
R
F

O
u
t
E
c
h
o
In
Antenna Control

25. Radar Equation
•The radar equation relates the range of a radar to the
characteristics of the transmitter, receiver, antenna, target,
and environment.
•It is useful for determining the maximum distance from the
radar to the target
•it can serve both as a tool for understanding radar operation
and as a basis for radar design.
•However it cannot give the precise value. Why??
•Statistical nature of noise and signal
•Fluctuation & uncertainty of the target
•Propagation effect of the wave
•Losses
•Are affecting the calculation
•We will consider each one separately.

29. The Radar Equation- Considerations
of various parameters
•As I pointed out earlier there are many factors which we have
to consider in the range equation. They affect the calculation.
•But we can model them and mathematically find the model
and insert in the range equation.
•Noise is in the system and it is random. So we have to have
probability.
•If affects the detection. So we have to get SNR
•Pulse repetition frequency
•Cross section of the target exposed to the wave we send

30. Questions?