Radar Communication

(BEC714D)

Module 1
Introduction to RADAR

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 SYLLABUS
• Module-1
Introduction to RADAR: Basic Radar, Simple
Radar equation, Radar Block diagram, Radar
Frequencies, Applications of Radar.
The RADAR Equation: Detection of signals in
Noise, Receiver Noise and SNR, Integration of
Radar Pulses, Radar Cross section of Targets,
Radar Cross section Fluctuations, Transmitter
Power, Pulse Repetition Frequency, Antenna
parameters, System Losses.
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 Learning Resources:
Text Books:
1) Merrill L. Skolnik, “Introduction to RADAAR Systems”, 3rd edition, Mc
Graw Hill Education (India) Private Limited, 2016 (Reprint), ISBN 978-0-
07-044533-8.
2) Habibur Rahman, “Fundamental Principles of RADAR”, CRC Press, 2019,
ISBN: 978-1-138-38779-9.

Reference Books:
3) Mark A Richards, James A. Scheer, William A. Holm, “Principles of
Modern RADAR”, Yesdee Publishing Private Ltd, , 2012, ISBN: 978-93-
80381-29-9.
4) Bassem R. Mahafza, “ Radar Systems Analysis and Design using
MATLAB”, 4th edition, CRC press, 2022, ISBN 978-0-367-50793-0.

5) J.C. Toomay, Paul J. Hannen; “Principles of Radar”, Third Edition, PHI

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Learning Pvt Ltd., 2011, ISBN : 978 81-203-4155-9.
Basic Radar
• RADAR is a contraction of the words
“Radio Detection and Ranging”.
• Radar is an electromagnetic system.
• It is used for the detection & location of reflecting
objects such as –
 Aircrafts
 Ships
 Spacecraft
 Vehicles
 People
 Natural Environment
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 Origin of RADAR
• Radar history began in the late 19th century with Heinrich Hertz's experiments
showing radio waves reflect off metallic objects.
• The theory was based on James Clerk Maxwell's work on electromagnetism.
• In 1904, German inventor Christian Hulsmeyer patented a simple radar-like
device for ship collision avoidance in fog.
• True modern radar systems using short pulses for range and direction
determination were developed mainly in the 1930s.
• From 1934 to 1939, eight countries (UK, Germany, US, USSR, Japan,
Netherlands, France, Italy) independently developed radar technologies,
mostly for military uses.
• Britain’s Robert Watson-Watt demonstrated practical aircraft detection radar in
1935, leading to the Chain Home system operational by 1938.
• The US Navy coined the term RADAR (Radio Detection and Ranging) around
1939-1940.
• Early US radars included SCR-268(Signal Corp Radio number) and SCR-270
used for antiaircraft control and aircraft detection, with SCR-270 detecting the
Pearl Harbor attack in 1941.
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• Radar played a critical role in World War II(1939-45) for air
defense & early warning. The development of the cavity
magnetron in the UK enabled smaller, higher resolution radars
during the war.
• Key post-war advances included travelling wave tubes, phased
array radars, higher frequencies for better resolution, and digital
signal processing with computers.
• In the 1950s, Doppler radar techniques, moving target indication,
and portable sentry radars were developed for battlefield use.
• Cold War radar innovation included side-looking airborne radar to
monitor enemy borders and vast early warning radar networks.
• Discoveries like radio wave ionosphere reflection allowed radars
to overcome terrain limits and extend range.
• Later technological improvements increased radar power and
range, enabling missile launch detection from thousands of miles
away.
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Basic Radar (Contd.)
• Radar operates by radiating energy into space
& detecting the echo signal reflected from an
object, or target.
• The reflected energy that is returned to the
radar –
Indicates the presence of a target.
Determines location along with other target-
related information (by comparing the received
echo signal with the transmitted signal).
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Basic Radar (Contd.)
• Radar can perform its function at long or short
distances & under conditions impervious to
optical & infrared sensors.
• It can operate in –
 Darkness
 Haze
 Fog
 Rain
 Snow
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Basic Radar (Contd.)
• Radar’s important attributes are –
 It has ability to measure distance with high
accuracy.
 It has ability to operate in all weather
conditions.
• The basic principle of radar is illustrated in
Fig.1.1.

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Basic principle of RADAR

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Basic Radar (Contd.)
• A transmitter (in the upper left portion of the figure),
generates an electromagnetic signal (such as a short
pulse of sinewave).
• This signal is radiated into space by an antenna.
• A portion of the transmitted energy is intercepted by the
target.
• This intercepted energy is reradiated by the target in
many directions.
• The reradiation directed back towards the radar is
collected by the radar antenna.
• The radar antenna now delivers it to a receiver.
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Basic Radar (Contd.)
• In the receiver, it is processed to detect the presence of the
target & determine its location.
• A single antenna is usually used on a time-shared basis.
• This is useful for both transmitting & receiving when the
radar waveform is a repetitive series of pulses.
• The range, or distance, to a target is found by measuring
the time it takes for the radar signal to travel to the target
& return back to the radar.
• The target’s location, in angle, can be found from the
direction in which the narrow-beamwidth radar antenna
points, when the received echo signal is of maximum
amplitude.
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Basic Radar (Contd.)
• If the target is in motion, there is a shift in the frequency of the echo
signal due to the doppler effect.
• This frequency shift is proportional to the velocity of the target
relative to the radar (also called the radial velocity).
• This frequency shift is called the doppler frequency shift.
• The doppler frequency shift is widely used in radar.
• It is the basis for separating desired moving targets from fixed
(unwanted) “clutter” echoes reflected from the natural environment
such as –
 Land
 Sea
 Rain
• Radar can also provide information about the nature of the target
being observed.
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Basic Radar (Contd.)
• The term radar is a contraction of the words radio detection
and ranging.
• The name reflects the importance placed by the early workers in
this field on the need for a device to –
 Detect the presence of a target.
 To measure the range of the target from it.
• Modern radars can extract more information from a target’s
echo signal than its range.
• Still, the measurement of range is one of its most important
functions.
• There are no competitive techniques other than radar that can
accurately measure long ranges in both clear & adverse weather.

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Basic Radar (Contd.)
[Range to a Target]
• The most common radar signal, or waveform, is a series of
short-duration pulses.
• These pulses are somewhat rectangular-shaped &
modulating a sinewave carrier.
• This is sometimes called a pulse train.
• The range to a target is determined by the time T R it takes
the radar signal to travel to the target & back.
• Electromagnetic energy in free space travels with the speed
of light, which is c=3*(10^8) m/s.
• Thus, the time for the signal to travel to a target located at a
range R & return back to the radar is 2R/c.
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 Basic Radar (Contd.)
[Range to a Target]
• The range to a target is then
R= (cTR)/2 ---------------------------- [1.1]
• With the range in kilometers or in nautical miles, & T
in microseconds, Eq.(1.1) becomes
R(km)=0.15 TR (μs) or R(nmi)=0.081 TR (μs)
• Each microsecond of round-trip travel time
corresponds to a distance of 150 meters, 164 yards,
492 feet, 0.081 nautical mile, or 0.093 statute mile.
• It takes 12.35 μs for a radar signal to travel a nautical
mile & back.
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Basic Radar (Contd.)
[Maximum Unambiguous Range]
• Once a signal is radiated into space by a radar, sufficient time
must elapse to allow all echo signals to return to the radar before
the next pulse is transmitted.
• The rate at which pulses may be transmitted, therefore, is
determined by the longest range at which targets are expected.
• If the time between pulses TP is too short, an echo signal from a
long-range target might arrive after the transmission of the next
pulse.
• In such a situation, it will be mistakenly associated with the next
pulse rather than the actual pulse transmitted earlier.
• This can result in an incorrect or ambiguous measurement of the
range.
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 Basic Radar (Contd.)
[Maximum Unambiguous Range]
• Echoes that arrive after the transmission of the next
pulse are called second-time-around echoes (or multiple-
time-around echoes if from even earlier pulses).
• Such an echo would appear to be at a closer range than
actual & its range measurement could be misleading.
• This is because it is not known that it is a second-time-
around echo.
• The range beyond which targets appear as second-
time-around echoes is the maximum unambiguous
range, Run.

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Basic Radar (Contd.)
[Maximum Unambiguous Range]
• The maximum unambiguous range is given by,
Run = (cTp)/2 = c/(2fP) ------------------- [1.2]
where TP = pulse repetition period = 1/f P, and
fP= pulse repetition frequency (prf), usually given in
hertz or pulses per second (pps).
• A plot of maximum unambiguous range as a function
of the pulse repetition frequency is shown in Fig.1.2.
• The term pulse repetition rate is sometimes used
interchangeably with pulse repetition frequency.
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Basic Radar (Contd.)
[Radar Waveforms]
• The typical radar utilizes a pulse waveform, an example
of which is shown in Fig.1.3.
• The peak power in this example is P t = 1 MW, pulse
width τ = 1 μs, and pulse repetition period T P = 1 ms =
1000 μs.
• The pulse repetition frequency fP is 1000 Hz, which
provides a maximum unambiguous range of 150 km, or
81 nmi.
• The average power (Pav) of a repetitive pulse-train
waveform is equal to (Pt*τ)/TP = Pt*τ*fP .
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Basic Radar (Contd.)
[Radar Waveforms]
• Hence, the average power in this case is
(106 * 10-6)/10-3 = 1 kW.
• The duty cycle of a radar waveform is defined
as the ratio of the total time the radar is
radiating to the total time it could have
radiated.
• This is τ/TP = τ*fP , or its equivalent Pav/Pt.
• In this case, the duty cycle is 0.001.

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Basic Radar (Contd.) [Radar Waveforms]

• The energy of the pulse is equal to Pt*τ, which is 1 J (joule).

• If the radar could detect a signal of 10 -12 W, the echo would be
180 dB below the level of the signal that was transmitted.
• A short-duration pulse waveform is attractive since the strong
transmitter signal is not radiating when the weak echo signal is being
received.
• A very long pulse is needed for some long-range radars to achieve
sufficient energy to detect small targets at long range.
• A long pulse, however, has poor resolution in the range dimension.
• Frequency or phase modulation can be used to increase the spectral
width of a long pulse to obtain the resolution of a short pulse.
• This is called pulse compression.
• Continuous wave (CW) waveforms have also been used in radar.

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Basic Radar (Contd.)
[Radar Waveforms]
• CW radars have to receive while transmitting.
• CW radars, hence, depend on the doppler frequency shift of the echo
signal.
• This shift is caused by a moving target.
• It is used to separate, in the frequency domain, the weak echo signal
from the large transmitted signal & the echoes from fixed clutter
(land, sea, or weather).
• It is also used to measure the radial velocity of the target.
• A simple CW radar does not measure range.
• However, it can obtain range by modulating the carrier with
frequency or phase modulation.
• Eg. Radio altimeter that measures the height (altitude) of an aircraft
above the earth.
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Basic Radar (Contd.)
[Radar Waveforms]
• Pulse radars that extract the doppler frequency shift are of 2
types-
 Moving Target Indication (MTI) Radars or
Pulse Doppler Radars.
• The above types depend on their particular values of pulse
repetition frequency & duty cycle.
• An MTI radar has a low prf & a low duty cycle.
• A pulse doppler radar, on the other hand, has a high prf and a
high duty cycle.
• Almost all radars designed to detect aircraft use the doppler
frequency shift.
• This is to reject the large unwanted echoes from stationary clutter.
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The Simple Form Of The Radar Equation
• The radar equation relates the range of a radar to the
characteristics of the –
 Transmitter
 Receiver
 Antenna
 Target
 Environment
• It is useful for -
 Determining the maximum range at which a particular
radar can detect a target.
 Understanding the factors affecting radar performance.
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The Simple Form Of The Radar Equation (Contd.)

• In this section, the simple form of the radar

range equation is derived.
• If the transmitter power Pt is radiated by an
isotropic antenna (one that radiates uniformly
in all directions), the power density at a
distance R from the radar is given by,

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The Simple Form Of The Radar Equation (Contd.)

• Power density is measured in units of watts per

square meter.
• Radars, however, employ directive antennas (with
narrow beamwidths) to concentrate the radiated
power Pt in a particular direction.
• The gain of an antenna is a measure of the
increased power density radiated in some direction
as compared to the power density that would
appear in that direction from an isotropic antenna.
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The Simple Form Of The Radar Equation (Contd.)

• The maximum gain G of an antenna may be

defined as

• The power density at the target from a

directive antenna with a transmitting gain G is
then

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The Simple Form Of The Radar Equation (Contd.)
• The target intercepts a portion of the incident energy
& reradiates it in various directions.
• It is only the power density reradiated in the
direction of the radar (the echo signal) that is of
interest.
• The radar cross section of the target determines the
power density returned to the radar for a particular
power density incident on the target.
• It is denoted by σ and is often called, for short,
target cross section, radar cross section, or simply
cross section.
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The Simple Form Of The Radar Equation (Contd.)

• The radar cross section is defined by the

following equation :

• The radar cross section has units of area, but it

can be misleading to associate the radar cross
section directly with the target’s physical size.
• Radar cross section is more dependent on the
target’s shape than on its physical size.
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The Simple Form Of The Radar Equation (Contd.)

• The radar antenna captures a portion of the

echo energy incident on it.
• The power received by the radar is given as
the product of the incident power density times
the effective area Ae of the receiving antenna.
• The effective area is related to the physical
area A by the relationship Ae=ρaA, where
ρa= antenna aperture efficiency.

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The Simple Form Of The Radar Equation (Contd.)

• The received signal power Pr (watts) is then

• The maximum range of a radar R max is the

distance beyond which the target cannot be
detected.
• It occurs when the received signal power P r
just equals the minimum detectable signal S min.
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The Simple Form Of The Radar Equation (Contd.)

• Substituting Smin=Pr in Eq.(1.6) and rearranging

the terms gives

• This is the fundamental form of the radar range

equation. It is also called for simplicity, the radar
equation or range equation.
• The important antenna parameters are the
transmitting gain & the receiving effective area.
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The Simple Form Of The Radar Equation (Contd.)

• The transmitter power Pt has not been

specified as either the average or the peak
power.
• It depends on how Smin is defined. Here, Pt
denotes the peak power.
• If the same antenna is used for both
transmitting & receiving, as it usually is in
radar, from antenna theory, we have

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The Simple Form Of The Radar Equation (Contd.)

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The Simple Form Of The Radar Equation (Contd.)

• These three forms of the radar equation given by

Eqs. (1.7), (1.9), and (1.10) are basically the same,
but with different interpretations.
• These simplified versions of the radar equation do
not adequately describe the performance of actual
radars.
• Many important factors are not explicitly included.
• Hence, it predicts too high a value of range,
sometimes by a factor of two or more.

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Radar Frequencies
• Conventional radars operate in what is called the microwave region
(a term not rigidly defined).
• Operational radars in the past have been at frequencies ranging from
about 100 MHz to 36 GHz.
• During World War II, letter codes such as S,X, and L were used to
designate the distinct frequency bands for microwave radar
development.
• The original purpose was to maintain military secrecy; but the letter
designations were continued after the war.
• They were a convenient shorthand means to readily denote the
region of spectrum at which a radar operated.
• Their usage is the accepted practice of radar engineers.
• Table 1.1 lists the radar-frequency letter-band designations approved
as an IEEE Standard.
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Band Nominal Frequency Range Specific ITU Radar Ranges Typical Applications
Over-the-horizon (OTH) radar,
HF 3 – 30 MHz – ionospheric propagation for very long-
range surveillance
Early warning radars, foliage
VHF 30 – 300 MHz 138–144, 216–225 MHz
penetration, long-range surveillance
Missile detection, space surveillance,
UHF 300 – 1000 MHz 420–450, 850–942 MHz
long-range tracking, foliage penetration
Air traffic control (ATC), en-route
L-band 1 – 2 GHz 1215–1400 MHz surveillance, early warning, long-range
weather radar
Weather radar (Doppler), terminal ATC
S-band 2 – 4 GHz 2300–2500, 2700–3700 MHz
radar, marine radar, surface surveillance

Weather monitoring, satellite altimeters,

C-band 4 – 8 GHz 5250–5925 MHz maritime navigation, some airport
surveillance radars

Fire-control radar, airborne intercept

radar, police speed radar, marine
X-band 8 – 12 GHz 8500–10,680 MHz
navigation radar, high-resolution
imaging

Tracking radars, missile guidance, short-

Ku-band 12 – 18 GHz 13.4–14.0, 15.7–17.7 GHz
range high-resolution surveillance

Short-range targeting, experimental

K-band 18 – 27 GHz 24.05–24.25 GHz
radars, police speed radars

High-resolution imaging, missile

Ka-band 27 – 40 GHz 33.4–36 GHz seekers, spaceborne cloud/precipitation
radars

Experimental high-resolution radars,

V-band 40 – 75 GHz 59–64 GHz
automotive collision-avoidance systems
Millimeter-wave imaging radar,
W-band 75 – 110 GHz 76–81, 92–100 GHz automotive radar (adaptive cruise
control), concealed weapon detection
126–142, 144–149, 231–235, 238–248 Advanced imaging radars, terahertz
mm-wave 110 – 300 GHz
GHz security scanners, atmospheric research
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Applications of Radar
• Radar has been employed to detect targets on the ground, on
the sea, in the air, in space, & even below ground.
• The major 8 areas of radar application are mentioned below.
 Military
 Remote Sensing
 Air Traffic Control (ATC)
 Law Enforcement & Highway Safety
 Aircraft Safety & Navigation
 Ship Safety
 Space
 Other

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Applications of Radar (Contd.)
• Military :
 Radar is an important part of air-defense systems as
well as the operation of offensive missiles & other
weapons.
 In air defense, it performs the functions of surveillance
& weapon control.
 A missile system might employ radar methods for
guidance & fuzing of the weapon.
 The military has been the major user of radar & the
major means by which new radar technology has been
developed.
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Applications of Radar (Contd.)
• Remote Sensing :
 All radars are remote sensors, but, this term is used
to imply the sensing of the environment.
 4 important examples of radar remote sensing are
Weather Observation ( weather forecast).
Planetary Observation (eg. Mapping of Venus
beneath its visually opaque clouds).
Short-range below-ground probing.
Mapping of sea ice to route shipping in an efficient
manner.
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Applications of Radar (Contd.)
• Air Traffic Control (ATC) :
 Radars have been employed around the world to
safely control –
Air traffic in the vicinity of airports
(Air Surveillance Radar, or ASR).
Air traffic en route from one airport to another
(Air Route Surveillance Radar, or ARSR).
Ground vehicular traffic.
Taxiing aircraft on the ground (Airport Surface
Detection Equipment, or ASDE).
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Applications of Radar (Contd.)
• Law Enforcement & Highway Safety :
 The radar speed meter, is used by police for
enforcing speed limits (A variation is used in
sports to measure the speed of a pitched
baseball).
 Radar has been considered for making vehicles
safer by warning of pending collision, actuating
the air bag, warning of obstructions or people
behind a vehicle.
 It is also employed for detection of intruders.
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Applications of Radar (Contd.)
• Aircraft Safety & Navigation :
 The airborne weather-avoidance radar outlines regions of
precipitation & dangerous wind shear to allow the pilot to
avoid hazardous conditions.
 Low-flying military aircraft rely on terrain avoidance &
terrain following radars to avoid colliding with
obstructions or high terrain.
 Military aircraft employ ground mapping radars to image
a scene.
 The radio altimeter is also a radar used to indicate the
height of an aircraft above the terrain & as a part of self-
contained guidance systems over land.
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Applications of Radar (Contd.)
• Ship Safety :
 Radar is found in ships & boats.
 This is for collision avoidance & to observe
navigational buoys, especially when the
visibility is poor.
 Similar shore-based radars are used for
surveillance of harbors & river traffic.

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Applications of Radar (Contd.)
• Space :
 Space vehicles have used radar for rendezvous
& docking, & for landing on the moon.
 They have also been used for planetary
explorations, especially the planet earth.
 Large ground-based radars are used for the
detection & tracking of satellites & other space
objects.

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Applications of Radar (Contd.)
• Other :
 Radar has also found application in industry
for the noncontact measurement of speed &
distance.
 It has been used for oil & gas exploration.
 Entomologists & Ornithologists have applied
radar to study the movements of insects &
birds, which cannot be easily achieved by
other means.
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Advantages of RADAR
• It can identify objects through darkness, haze, fog, rain and
snow.
• RADAR signal can penetrate through insulators such as
rubber and plastic materials.
• RADAR can identify stationary and moving objects.
Disadvantages of RADAR
• It can not identify the details like the human eyes in closed
distance.
• It can not identify the colour of the target.
• It can not identify the targets underwater because water
attenuates radio waves.
• It cannot detect objects placed behind conducting materials
such as metal sheets which block or reflect radar signals.
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RADAR Antenna Configurations

• Bistatic: The transmit and receive antennas are at

different positions as viewed from the target(e.g.,
ground transmitter and airborne receiver).
• Monostatic: The transmitter and receiver are
colocated as viewed from the target (i.e., the
same antenna is used to transmit and receive).
• Quasi-monostatic: The transmit and receive
antennas are highly separated but still appear to
be at the same location as viewed from the
target(e.g., separate transmit and receive antennas
on the same aircraft).
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 Block diagram of RADAR
• The operation of pulse RADAR is described with a simple block
diagram.
• There are two sections of RADAR system
1) Transmitter 2) Receiver

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Prediction of Range Performance

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Detection of signals in noise

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Figure 2.1 Envelope of the RADAR receiver output as a function of time
(or range).
A,B and C represent signal plus noise. A and B would be valid detections but C is a missed
detection.

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Receiver noise and Signal to Noise Ratio

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Integration of RADAR pulses

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 The cathode-ray-tube (CRT) display shows the radar echoes as blips or traces.
 The eye and brain of the radar operator naturally integrate these blips over time— meaning, the operator can
observe repeated echoes and mentally “add them up” to detect a target that may not be visible in a single radar
pulse.

• Example: If a target is weak and its echo is faint, it might be missed in one pulse. But when many pulses are
displayed on the CRT, the eye notices the consistent spot appearing at the same location, and the brain integrates
this information → allowing detection.
• So, the statement highlights that human vision and perception work together with the radar display as an
integration method.
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Radar cross section of targets

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Simple Targets

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Transmitter Power

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PRF and Range ambiguities

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 System Losses
• The losses within the radar system is called system
losses. The losses in a radar system reduce the
signal-to-noise ratio at the receiver output.
1)Microwave plumbing losses : There is always
loss in the transmission line that connects the
antenna to the transmitter and receiver. In addition
there can be loss in the various microwave
components, such as duplexer, receiver protector,
rotary joints, directional couplers, transmission line
connectors, bends in the transmission lines and the
mismatch at the antenna.
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a) Transmission line losses: Generally same
transmission line used for both transmission and
reception , the loss to be inserted in the radar eq
is twice the one way loss. At lower radar
frequencies, the transmission line introduces
little loss. At higher radar frequencies
attenuation may not be small and may have to be
taken in account. In practical the transmitter and
receiver should be placed close to the antenna to
keep the transmission line loss small.

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b) Duplexer loss: the loss due to a gas duplexer
that protects the receiver from the high power of
the transmitter is generally different on
transmission and reception. It also depends on
the type of duplexer used.

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2) Antenna Losses :
a) Beam shape loss: In radar equation antenna gain is assumed
as constant at its maximum value but in practice as a search
antenna scans across a target, it does not offer its peak gain to all
echo pulses. When the system integrates several echo pulses
maximum antenna gain occurs when the peak of antenna beam is
in direction of target.

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b) Scanning loss: When a radar antenna scans rapidly compared
to round trip time of the echo signal, the antenna gain may not
be same for transmission and while receiving of echoes. This
results in the direction of additional loss called the Scanning
loss. The scanning loss is most significant in long range
scanning radars, such as space surveillance and ballistic missile
defense radars.
c) Radome: The loss introduced by radome is decided by its
type and operating frequency. A commonly used ground based
metal space frame radome offers a loss of 1.2dB for two way
transmission.
d) Phased array losses: Some phased array radars have
additional transmission line losses due to the distribution
network that connects the receiver and transmitter to multiple
elements of array. These losses reduces antenna power gain.
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3) Signal Processing Losses: For detecting targets in
clutters and in extracting information from the radar
echo signals is very important and lossless signal
processing is necessary. Various losses accounted during
signal processing are:

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4) Losses in Doppler-Processing Radar:
There can be an eclipsing loss in pulse doppler radars
when echoes from (ambiguous) multiple-time around
targets arrive back at the radar at the same time that a
pulse is being transmitted. MTI doppler processing also
introduces loss due to the shape of the doppler
(velocity) filters if the target velocity does not
correspond to the maximum response of the doppler
filter. Fill pulses in MTI and pulse doppler radar
sometimes are necessary, but they represent wasted
pulses from the point of view of detection of signals in
noise.

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5) Collapsing Loss :
When additional noise samples are integrated with
signal + noise pulses, this added noise causes
degradation called Collapsing Loss.
The collapsing loss is given by,

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6) Operator Loss:
• Most modern high-performance radars provide
the detection decision automatically without the
intervention of a human operator.
• Processed information is presented directly to an
operator or to a computer for some other action.
• In the early days of radar, operators were
depended upon to find targets on a display.
• Sometimes when the radar range performance
was less than predicted, the degradation of
performance was attributed to an operator loss.
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7) Equipment degradation:
• It is not uncommon for radars operated under field
conditions to have lower performance than when they
left the factory.
• This loss of performance can be recognized and
corrected by regularly testing the radar, especially with
built-in test equipment that automatically indicates
when equipment deviates from specifications.
• It is not possible to be precise about the amount of loss
to be assigned to field degradation .
• From 1 to 3dB might be used when no other
information is available.
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8) Propagation Effects:
• The propagation effects of radar wave has significant
impact on losses.
• Propagation effects are not computed under system
loss but under propagation factor.
• Major effects of propagation on radar performance
are :
1) Reflection from earth’s surface
2) Refraction
3) Propagation in atmospheric ducts
4) Attenuation in clear atmosphere

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