Radar Systems: Lecture Notes ON

Smartzworld.com Smartworld.
asia
LECTURE NOTES
ON
RADAR SYSTEMS
IV B.Tech II semester (JNTUH-R13)
ELECTRONICS AND COMMUNICATION ENGINEERING
jntuworldupdates.org Specworld.in
Smartzworld.com Smartworld.asia
SYLLABUS
UNIT–I:
BASICS OF RADAR: Introduction, Maximum unambiguous Range, Simple form of Radar Equation Radar
Block diagram and Operation Radar Frequencies and Applications, Prediction of Range Performance,
Minimum Detectable Signal, Receiver Noise, Modified Radar Range Equation, Illustrative problems
RADAR EQUATION: SNR, Envelope Detector, False Alarm Time and Probability, Integration of Radar Pulses,
Radar Cross Section of Targets (simple targets - sphere, cone-sphere), Transmitter Power, PRF and Range
Ambiguities, System Losses (qualitative treatment), Illustrative Problems.
UNIT–II:
CW AND FREQUENCY MODULATED RADAR: Doppler Effect, CW Radar – Block Diagram, Isolation
between Transmitter and Receiver, Non-zero IF Receiver, Receiver Bandwidth Requirements, Applications of CW
radar, Illustrative Problems.
FM-CW Radar, Range and Doppler Measurement, Block Diagram and Characteristics (Approaching/ Receding
Targets), FM-CW altimeter, Multiple Frequency CW Radar.
UNIT–III:
MTI AND PULSE DOPPLER RADAR: Introduction, Principle, MTI Radar with - Power Amplifier Transmitter
and Power Oscillator Transmitter, Delay Line Cancellers – Filter Characteristics, Blind Speeds, Double
Cancellation, And Staggered PRFs. Range Gated Doppler Filters, MTI Radar Parameters, Limitations to MTI
Performance, MTI versus Pulse Doppler radar.
UNIT–IV:
TRACKING RADAR: Tracking with Radar, Sequential Lobing, Conical Scan, Monopulse Tracking Radar–
Amplitude Comparison Monopulse (one- and two coordinates), Phase Comparison Monopulse, Tracking in Range,
Acquisition and Scanning Patterns, Comparison of Trackers.
UNIT–V:
DETECTION OF RADAR SIGNALS IN NOISE: Introduction, Matched Filter Receiver – Response
Characteristics and Derivation, Correlation Function and Cross-correlation Receiver, Efficiency of Nonmatched
Filters, Matched Filter with Non-white Noise.
RADAR RECEIVERS: Noise Figure and Noise Temperature, Displays – types. Duplexers – Branch type and
Balanced type, Circulators as Duplexers. Introduction to Phased Array Antennas – Basic Concepts, Radiation
Pattern, Beam Steering and Beam Width changes, Series versus Parallel Feeds, Applications, Advantages and
Limitations.
TEXT BOOKS:
1.Introduction to Radar Systems Merrill I Skolnik, TMH Special Indian Edition, 2nd edition, 2007
REFERENCES:
1. Introduction to radar systems-Merrill I.Skolnik 3rd Ed., TMH, 2001
2. Radar: Principles, Technology, Applications- Byron Edde, Pearson Education, 2004
3. Radar Principles- Peebles, Jr. P.Z Wiley, New York, 1998
UNIT-I
NATURE OF
RADAR
INTRODUCTION:
The name Radar stands 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 < l < 75 cm)
2. Active technique: radiation is emitted by radar – radiation scattered by objects is

detected by radar.
Radar is an electromagnetic system for the detection and location of

objects (Radio Detection and Ranging). Radar operates by transmitting a particular type of
waveform and detecting the nature of the signals reflected back from objects.
Radar can’ t resolve detail or color as well as the human eye (an optical frequency
passive scatter meter).
Radar can see in conditions which do not permit the eye to see such as darkness,
haze, rain, smoke.
Radar can also measure the distances to objects. The elemental radar system consists of
a transmitter unit, an antenna for emitting electromagnetic radiation and receiving the
echo, an
Energy detecting receiver and a processor.
A portion of the transmitted signal is intercepted by a reflecting object (target) and is

reradiated in all directions. The antenna collects the returned energy in the backscatter
direction and delivers it to the receiver. The distance to the receiver is determined by measuring
the time taken for the electromagnetic signal to travel to the target and back.
The direction of the target is determined by the angle of arrival (AOA) of the reflected
signal. Also if there is relative motion between the radar and the target, there is a shift in
frequency of the reflected signal (Doppler Effect) which is a measure of the radial component
of the relative velocity. This can be used to distinguish between moving targets and stationary
ones.
Radar was first developed to warn of the approach of hostile aircraft and for directing
anti aircraft weapons. Modern radars can provide AOA, Doppler, and MTI etc.
10
RADAR RANGE MEASUREMENT
11
T get
• Target range =
2
where c = eed of light
= round trip time
12
The simplest radar waveform is a train of narrow (0.1μs to 10μs) rectangular

pulses modulating a sinusoidal carrier the distance to the target is determined from the
time T R taken by the pulse to travel to the target and return and from the knowledge
that electromagnetic energy travels at the speed of light.
Since radio waves travel at the speed of light (v = c = 300,000

km/sec)
Range =
c×time/2
The range or distance, R = cTR/2
R (in km) = 0.15TR (μs) ; R (in nmi) = 0.081TR (μs)
NOTE:
 1 nmi = 6076 feet =1852 meters.

 1 Radar mile = 2000 yards = 6000 feet
 Radar mile is commonly used unit of distance.
NOTE:
Electromagnetic energy travels through air at approximately the speed of light:-
13
1. 300,000 kilometers per second.
2. 186,000 statute miles per second.
3. 162,000 nautical miles per second.
Once the pulse is transmitted by the radar a sufficient length of time must
elapse before the next pulse to allow echoes from targets at the maximum range to be
detected. Thus the maximum rate at which pulses can be transmitted is determined by
the maximum range at which targets are expected. This rate is called the pulse
repetition rate (PRF).
If the PRF is too high echo signals from some targets may arrive after the
transmission of the next pulse. This leads to ambiguous range measurements. Such
pulses are called second time around pulses.
The range beyond which second time around pulses occur is called the maximum
unambiguous range.
RUNAMBIG = c/2f P Where fP is the PRF in Hz.
More advanced signal waveforms then the above are often used, for example
the carrier maybe frequency modulated (FM or chirp) or phase modulated
(pseudorandom bi phase) too permit the echo signals to be compressed in time after
reception. This achieves high range resolution without the need for short pulses and
hence allows the use of the higher energy of longer pulses. This technique is called
pulse compression. Also CW waveforms can be used by taking advantage of the Doppler
shift to separate the received echo from the transmitted signal.
Note: unmodulated CW waveforms do not permit the measurement of range.
14
What is done by Radar?
Radar can see the objects in
day or night
rain or shine
land or air
cloud or clutter
fog or frost
earth or planets
stationary or moving and
Good or bad weather.
In brief, Radar can see the objects hidden any where in the globe or planets except
hidden behind good conductors.
15
INFORMATION GIVEN BY THE RADAR:
Radar gives the following information:
 The position of the object

 The distance of objects from the location of radar
 The size of the object
 Whether the object is stationary or moving
 Velocity of the object
 Distinguish friendly and enemy aircrafts
 The images of scenes at long range in good and adverse weather conditions
 Target recognition
 Weather target is moving towards the radar or moving away
 The direction of movement of targets
 Classification of materials
NATURE AND TYPES OF RADARS:
The common types of radars

are:
 Speed trap Radars
 Missile tracking Radars
 Early warning Radars
16
 Airport control Radars
 Navigation Radars
 Ground mapping Radars
 Astronomy Radars
 Weather forecast Radars
 Gun fire control Radars
 Remote sensing Radars
 Tracking Radars
 Search Radars
 IFF (Identification Friend or Foe)
 Synthetic aperture Radars
 Missile control Radars
 MTI (Moving Target Indication) Radars
 Navy Radars
 Doppler Radars
 Mesosphere, Stratosphere and Troposphere (MST) Radars
 Over-The-Horizon (OTH) Radars
 Mono pulse Radars

17
 Phased array Radars
 Instrumentation Radars
 Gun direction Radars
 Airborne weather Radars
18
PULSE CHARACTERISTICS OF RADAR SYSTEMS:
There are different pulse characteristics and factors that govern them in a Radar system
Carrier
Pulse width
Pulse Repetition Frequency (PRF)
U n a m b i g u o u s Range
NOTE: ECHO is a reflected EM wave from a target and it is received by a Radar receiver.
CARRIER: The carrier is used in a Radar system is an RF(radio frequency) signal with
microwave frequencies.
Carrier is usually modulated to allow the system to capture the required

data.
In simple ranging Radars, the carrier will be pulse modulated but in continuous wave
systems such Doppler radar modulation is not required.
19
In pulse modulation, the carrier is simply switched ON & OFF in synchronization.
PULSE WIDTH: The pulse width of the transmitted signal determines the dead zone. When the
Radar transmitter is active, the receiver input is blanked to avoid the damage of amplifiers. For
example, a Radar echo will take approximately 10.8 µsec to return from 1 standard mile away
target.
PULSE REPETITION FREQUENCY (PRF): PRF is the number of pulses transmitted per second.
PRF is equal to the reciprocal of pulse repetition time (PRT). It is measured in Hertz
PRF = 1/PRT
Pulse Interval Time or Pulse Reset Time (PRT) is the time interval between two pulses. It is
expressed in milliseconds.
Pulse Reset Time = Pulse Repetition Time – Pulse Width
UNAMBIGUOUS RANGE: In simple systems, echoes from targets must be detected and
processed before the next transmitter pulse is generated if range ambiguity is to be avoided.
20
Range ambiguity occurs when the time taken for an echo to return from a target is greater
than the pulse repetition period (T).
Echoes that arrive after the transmission of the next pulse are called as second-time-
around echoes.
The range beyond which targets appear as second-time-around echoes is called as the
Maximum
Unambiguous Range and is given by
RUNAMBIG = c/2fP
c = velocity of propagation Where, TP = fP
21
fP is the PRF(PULSE REPETITION FREQUENCY) in Hz
TYPES OF BASIC RADARS:
Monostatic and Bistatic
CW
FM-CW
Pulsed radar
Monostatic radar uses the same antenna for transmit and receive. Its typical geometry is shown
in the below fig.
22
Bistatic radars use transmitting and receiving antennas placed in different

locations.
CW radars, in which the two antennas are used, are not considered to be bistatic radars as the
distance between the antennas is not considerable. The bistatic radar geometry is shown in
below fig.
23
24
RADAR WAVE FORMS:
The most common Radar waveform is a train of narrow, rectangular shape pulses modulating
a sine-wave carrier.
The figure shows a pulse waveform, which can be utilized by the typical Radar.
25
26
From the given Radar waveform:
Peak power pt = 1 Mwatt
Pulse Width τ = 1 µsec.
Pulse Repetition Period TP = 1 msec.
A maximum unambiguous range of 150 km was provided by the PRF fP = 1000 Hz.
RUNAMBIG = c/2fP ==> 150×103 = 3×108 / 2fP
==> fP = 1000 Hz.
Then, the average power Pavg of a repetitive pulse train wave form is given by Pavg = pt τ/TP ==>
Pavg = pt τ fP
In this case, Pavg = 1 Kwatt
For a Radar wave form, the ratio of the total time that the Radar is radiating to the total time
it could have radiated is known as duty cycle.
27
Duty Cycle = τ/TP = τ fP = Pavg /pt
Duty Cycle = τ/TP = 0.001
The energy of the pulse is given by, E = τ pt = 1 Joule.
The Radar waveform can be extended in space over a distance of 300 meters using a pulse
width of 1 µsec.
i.e., Distance = c τ = 300 m.
Half of the above distance (i.e. c τ/2) can be used to recognize the two equal targets which
are being resolved in range. In this case, a separation of 150m between two equal size targets
can be used to resolve them.
28
Name Symbol Units Typical values

Transmitted
Frequency ft MHz, G hz 1000-12500 Mhz

Wavelength cm 3-10 cm
Pulse Duration sec 1 sec
Pulse Length h m 150-300 m (h=c
Pulse Repetition
Frequency PRF sec-1 1000 sec-1

Interpulse Period T Milli sec 1 milli sec
Peak Transmitted
Power Pt MW 1 MW
Average Power Pavg kW 1 kW (Pavg = Pt PRF)
Received Power Pr mW 10-6 mW
The Radar Range Equation:
The radar range equation relates the range of the radar to the characteristics of the
transmitter, receiver, antenna, target and the environment.
It is used as a tool to help in specifying radar subsystem specifications in the design

phase of a program. If the transmitter delivers PT Watts into an isotropic antenna, then
the power density (w/m2) at a distance R from the radar is
29
Pt/4πR2
Here the 4πR2 represents the surface area of the sphere at distance R
Radars employ directional antennas to channel the radiated power Pt in a particular

direction. The gain G of an antenna is the measure of the increased power radiated in
the direction of the target, compared to the power that would have been radiated from an
isotropic antenna
30
∴ Power density from a directional antenna = PtG/4πR2
The target intercepts a portion of the incident power and redirects it in various
directions.
The measure of the amount of incident power by the target and redirected back in the direction
of the radar is called the cross section σ.
Hence the Power density of the echo signals at the radar =
Note: the radar cross-section σ has the units of area. It can be thought of as the size of the
target
as seen by the radar.
The receiving antenna effectively intercepts the power of the echo signal at the radar
over a certain area called the effective area Ae.
Since the power density (Watts/m2) is intercepted across an area Ae, the power
delivered to the receiver is
Pr = (PtGσAe) /(4πR2)2 ==> R4 = (PtGσAe) /(4π)2 Pr
31
R = [(PtGσAe) /(4π)2 Pr]1/4
Now the maximum range Rmax is the distance beyond which the target cannot be
detected due to insufficient received power Pr, the minimum power which the receiver can
detect is called the minimum detectable signal Smin. Setting, Pr = Smin and rearranging the above
equation gives
Note here that we have both the antenna gain on transmit and its effective area on receive.
These are related by:
As long as the radar uses the same antenna for transmission and reception we have
32
Example: Use the radar range equation to determine the required transmit power for the
TRACS
radar given: Prmin =10-13 Watts, G=2000, λ=0.23m, PRF=524, σ=2.0 m2
Now,
From
= 3.1 MW
Note 1: these three forms of the equation for Rmax varywith different powers of λ. This
results
from implicit assumptions about the independence of G or Ae from λ.
Note 2: the introduction of additional constraints (such as the requirement to scan a

specific volume of space in a given time) can yield other λ dependence.
33
Note 3: The observed maximum range is often much smaller than that predicted from the
above equation due to the exclusion of factors such as rainfall attenuation, clutter, noise figure
etc.
RADAR BLOCK DIAGRAM AND OPERATION:
The Transmitter may be an oscillator (magnetron) that is pulsed on and off bya modulator
to generate the pulse train.
the magnetron is the most widely used oscillator
typical power required to detect a target at 200 NM is MW peak power and several kW
average power
typical pulse lengths are several μs
typical PRFs are several hundreds of pulses per second
34
The waveform travels to the antenna where it is radiated. The receiver must be
protected from damage resulting from the high power of the transmitter. This is done by the
duplexer.
duplexer also channels the return echo signals to the receiver and not to the transmitter
duplexer consists of 2 gas discharge tubes called the TR (transmit/receive) and the and an
ATR (anti transmit/receive) cell
The TR protects the receiver during transmission and the ATR directs the echo to
the receiver during reception.
solid state ferrite circulators and receiver protectors with gas plasma (radioactive
keep alive) tubes are also used in duplexers
35
The receiver is usually a superheterodyne type. The LNA is not always desirable. Although it
provides better sensitivity, it reduces the dy namic range of operation of the mix er. A receiver
with just a mixer front end has greater dynamic range, is less susceptible to overload and is less
vulnerable to electronic interference.
The mixer and Local Oscillator (LO) convert the RF frequency to the IF frequency.
The IF is typically 300MHz, 140Mz, 60 MHz, 30 MHz with bandwidths of 1 MHz to 10
MHz.
36
The IF strip should be designed to give a matched filter output. This requires its H(f) to
maximize the signal to noise power ratio at the output.
This occurs if the |H(f)| (magnitude of the frequency response of the IF strip is equal
to the signal spectrum of the echo signal |S(f)|, and the ARG(H(f)) (phase of the
frequency response) is the negative of the ARG(S(f)).
i.e. H(f) and S(f) should be complex conjugates
For radar with rectangular pulses, a conventional IF filter characteristic approximates a
matched filter if its bandwidth B and the pulse width τ satisfy the relationship
37
38
The pulse modulation is extracted by the second detector and amplified by video
amplifiers to levels at which they can be displayed (or A to D’d to a digital processor). The
display is usually a CRT; timing signals are applied to the display to provide zero range
information. Angle information is supplied from the pointing direction of the antenna.
The most common type of CRT display is the plan position indicator (PPI) which maps
the location of the target in azimuth and range in polar coordinates
The PPI is intensitymodulated bythe amplitude of the receiver output and the CRT
electron beam sweeps outward from the centre corresponding to

range.
Also the beam rotates in angle in synchronization with the antenna pointing angle.
A B scope display uses rectangular coordinates to display range vs angle i.e. the x axis is
angle and the y axis is range.
Since both the PPI and B scopes use intensity modulation the dynamic range is limited
An A scope plots target echo amplitude vs range on rectangular coordinates for

some fixed direction. It is used primarily for tracking radar applications than for
surveillance radar.
The simple diagram has left out many details such as
AFC to compensate the receiver automatically for changes in the transmitter
AGC
Circuits in the receiver to reduce interference from other radars
39
Rotary joints in the transmission lines to allow for movement of the antenna
MTI (moving target indicator) circuits to discriminate between moving targets and
unwanted stationary targets
Pulse compression to achieve the resolution benefits of a short pulse but with the
energy benefits of a long pulse.
Monopulse tracking circuits for sensing the angular location of a moving target
and allowing the antenna to lock on and track the target automatically
Monitoring devices to monitor transmitter pulse shape, power load and

receiver sensitivity
40
Built in test equipment (BITE) for locating equipment failures so that faulty circuits can
be replaced quickly
Instead of displaying the raw video output directly on the CRT, it might be digitized and
processed and then displayed. This consists of:
Quantizing the echo level at range-azimuth resolution cells
Adding (integrating) the echo level in each cell
Establishing a threshold level that permits only the strong outputs due to target echoes
to pass while rejecting noise
Maintaining the tracks (trajectories) of each target
Displaying the processed information
This process is called automatic tracking and detection (ATD) in surveillance radar
Antennas:
The most common form of radar antenna is a reflector with parabolic shape, fed from
a point source (horn) at its focus
41
The beam is scanned in space by mechanically pointing the antenna
Phased array antennas are sometimes used. Her the beam is scanned by varying the
phase of the array elements electrically
Radar Frequencies:
Most Radar operates between 220 MHz and 35 GHz.
Special purpose radars operate out side of this range.
Skywave HF-OTH (over the horizon) can operate as low as 4 MHz
Groundwave HF radars operate as low as 2 MHz
Millimeter radars operate up to 95 GHz
Laser radars (lidars) operate in IR and visible spectrum
42
The radar frequencyletter -band nomenclature is shown in the table. Note that the
frequencyassignment to the latter band radar (e.g. L band radar) is much smaller than
the complete range of frequencies assigned to the letter band
43
Applications of Radar
General
i. Ground-based radar is applied chiefly to the detection, location and tracking of aircraft
of space targets
44
ii. Shipborne radar is used as a navigation aid and safety device to locate buoys,
shorelines and other ships. It is also used to observe aircraft
iii. Airborne radar is used to detect other aircraft, ships and land vehicles. It is also used
for mapping of terrain and avoidance of thunderstorms and terrain.
iv. Spaceborne radar is used for the remote sensing of terrain and sea, and
for rendezvous/docking.
45
Major Applications
1. Air Traffic Control
Used to provide air traffic controllers with position and other information
on aircraft flying within their area of responsibility (airways and in the vicinity of
airports)
High resolution radar is used at large airports to monitor aircraft and

ground vehicles on the runways, taxiways and ramps.
GCA (ground controlled approach) or PAR (precision approach radar) provides

an operator with high accuracy aircraft position information in both the
vertical and horizontal. The operator uses this information to guide the
aircraft to a landing in bad weather.
MLS (microwave landing system) and ATC radar beacon systems are based on
radar technology
2. Air Navigation
Weather avoidance radar is used on aircraft to detect and display areas of

heavy precipitation and turbulence.
Terrain avoidance and terrain following radar (primarily military)
Radio altimeter (FM/CW or pulse)
Doppler navigator
Ground mapping radar of moderate resolution sometimes used for navigation
3. Ship Safety
46
These are one of the least expensive, most reliable and largest applications
of radar
Detecting other craft and buoys to avoid collision
Automatic detection and tracking equipment (also called plot extractors)

are available with these radars for collision avoidance
Shore based radars of moderate resolution are used from harbour surveillance
and
as an aid to navigation
4. Space
Radars are used for rendezvous and docking and was used for landing on
the moon
47
Large ground based radars are used for detection and tracking of satellites
Satellite-borne radars are used for remote sensing (SAR, synthetic aperture radar)
5. Remote Sensing
Used for sensing geophysical objects (the environment)
Radar astronomy - to probe the moon and planets
Ionospheric sounder (used to determine the best frequency to use for HF
communications)
Earth resources monitoring radars measure and map sea conditions, water
resources, ice cover, agricultural land use, forest conditions, geological
formations, environmental pollution (Synthetic Aperture Radar, SAR and Side
Looking Airborne Radar SLAR)
6. Law Enforcement
Automobile speed radars
Intrusion alarm systems
7. Military
Surveillance
Navigation , Fire control and guidance of weapons
48
ADVANTAGES OF BASIC RADAR:
It acts as a powerful eye.
It can see through: fog, rain, snow, darkness, haze, clouds and any insulators.
It can find out the range, angular position, location and velocity of targets.
LIMITATIONS:
Radar can not recognize the color of the targets.
It can not resolve the targets at short distances like human eye.
It can not see targets placed behind the conducting sheets.
It can not see targets hidden in water at long ranges.
49
It is difficult to identify short range objects.
The duplexer in radar provides switching between the transmitter and

receiver alternatively when a common antenna is used for transmission and
reception.
The switching time of duplexer is critical in the operation of radar and it affects
the minimum range. A reflected pulse is not received during
the transmit pulse
subsequent receiver recovery time
The reflected pulses from close targets are not detected as they return before the
receiver is connected to the antenna by the duplexer.
Other Forms of the Radar Equation:-
FIRST EQUATION:-
If the transmit and receive antennas are not the same and
have different gains, the radar equation will
50
where Gt is the gain of transmit antenna and G r is the gain of receive antenna .
SECOND EQUATION:-
If the target ranges are different for transmit

and
. Where Rt
receive antennas. The equation will be :
and Rr are ranges between the target and the transmit antenna and the target and
the receive antenna respectively .
THIRD EQUATION:-
The first radar equation we discussed was derived without incorporating

losses of energy which accompany transmission, reception, and the processing of
electromagnetic radiation. It is sufficient to incorporate all of these losses in one term and
write equation as follows :- Where L is the total loss term.
51
FOURTH EQUATION:-
If we know that the signal power equals the .Note that

noise
all of
power S/N = 1 the equation will be :
The terms appearing in the Ro equation, with the exception of the target cross section, are
a characteristic of the radar system.
Once a design is established, Ro can be determined for a given target from the fourth
size. Using the value of Ro equation in the
third equation From this equation, it is noted that S/N is inversely

we get
.
proportional to the fourth power of

Range, R.
Parameters Affecting the Radar Range Equation:-
The radar equation was derived in the previous section and is below for reference:-
52
The terms of this equation, which depend on the:-
1) Physical structure of antenna. 2) Radar transmitter.
3) Processing of received signal. 4) System losses.
5) Characteristics of the target.
Type of Transmission:-
Passive: - there is no transmission.
Active: - there is transmission.
53
RADAR PARAMETERS AND DEFINITIONS:
RADAR: Radio means Radio Detection and Ranging. It is a device useful for detecting and
ranging, tracking and searching. It is useful for remote sensing, weather forecasting,
speed traping, fire control and astronomical abbrivations.
Echo: Echo is a reflected electromagnetic wave from a target and it is received by radar
receiver. The echo signal power is captured by the effective area of the receiving space antenna.
Duplexer: It is a microwave switch which connects the transmitter and receiver to the
antenna alternatively. It protects the receiver from high power output of the transmitter. It
allows the use of the single antenna for both radar transmistion and reception. It balnks the
receiver during the transmitting period.
Antenna: It is a device which acts as atransducer between transmitter and free space and
between free space and receiver. It converts electromagnetic energy into electrical energy at
receiving side and converts the electrical energy into electromagnetic energy at the
transmitting side. Antenna is a source and a sensor of electromagnetic waves. It is also
an impedence matching device and a radiator of electromagnetic waves.
Transmitter: It conditions the signals interest and connects them to the antenna. The
transmitter generates high power RF energy. It consists of magnetron or klystron or travelling
wave tube or cross field amplifier.
Receiver: It receives the signals from the receiving antenna and connects them to display.
The receiver amplifies weak return pulses and separates noise and clutter.
Synchronizer: It synchronizes and coordinates the timing for range determination. It regulates
PRF and resets for each pulse. Synchronizer connects the signals simultaneously to transmitter
and display. It maintains timing of transmitted pulses. It ensures that all components and
devices operate in a fixed time relationship.
54
Display: It isa device to present the received information for the operator to interpret.
It provides visual presentation of echoes.
55
Bearing or Azimuth Angle: It is an angle measured from true north in a horizontal plane.
In other words, it is the antenna beams angle on the local horizontal plane from some
reference. The reference is usually true north.
Elevation Angle: It is an angle measured between the horizontal plane and line of sight. In other
words, it is an angle between the radar beam antenna axis and the local horizontal.
Resolution: It is the ability to separate and detect multiple targets or multiple features on
the same target. In other words, it is the ability of radar to distinguish targets that are very
close in either range or bearing. The targets can be resolved in four dimensions range,
horizontal cross- range, vertical cross-range and Doppler shift.
Range Resolution (RS): It is the ability of Radar to distinguish two or more targets at
different ranges but at the same bearing. It has the units of distance.
RS = vo× (PM/2) in meters
Bearing Resolution: It is the ability of Radar to distinguish objects which are in different
bearing but at the same range. It is expressed in degrees.
Range of Radar: It is the distance of object from the location of radar, R = voΔt/2
Where, vo = velocity of EM wave, Δt = The time taken to receiver echo from the object.
Radar Pulse: It is a modulated radiated frequency carrier wave. The carrier frequency is the
transmitter oscillator frequency and it influences antenna size and beam width.
56
57
Cross-Range Resolution of Radar: It is the ability of Radar to distinguish multiple

targets at the same range. It has linear dimension perpendicular to the axis of the Radar
antenna. It is of two types:
A z im ut h (Horizontal) cross-range
Elevation (Vertical) cross-range
Narrow beam of radar antennas resolve closed spaced targets. The cross-range resolution Δx is
given by, Δx = Rλ/Leff
Where R = Target range in meters
Leff = Effective length of the antenna in the direction of the beam width is estimated.
λ = Wavelength in meters
Doppler Resolution: It is the ability to distinguish targets at the same range, but moving at
Different radial velocities. The Doppler resolution Δfd is given by, Δfd = 1/T d in Hz
Here Td = The look time in seconds.
58
The Doppler resolution is possible if Doppler frequencies differ by at least one cycle over the
time of observation. It depends on the time over which signal is gathered for processing.
Radar Signal: Radar signal is an alternating electrical quantity which conveys information. It
can be voltage or current. The different types of radar signals are:
Echoes from desired targets
Echoes from undesired targets
Noise signals in the receiver
Jamming signals
Signals from hostile sources
Radar Beam: It is the main beam of radar antenna. It represents the variation of a
field
strength or radiated power as a function of θ in free

space.
59
ECM: ECM represents Electronic Counter Measure. It is also known as jamming. It is an

electronic technique which distrup radar or communication.
Radar Beam Width: It is the width of the main beam of radar antenna between two half
power points or between two first nulls. It is expressed in degrees.
Search Radar: These are used for searching the targets and they scan the beam a few
times per minute. These are used to detect targets and find their range, angular velocity and
some times velocity. The different types of search radars are:
Surface Search Radar
Air Search Radar
Two-dimentional Search Radar
Three-dimentional Search Radar
Pulse Width: It is the duration of the radar pulse. It is expressed in milli seconds. The pulse
width influences the total pulse energy. It determines minimum range and range resolution. In,
fact it represents the transmitter ‘ON’ time.
Pulse Interval Time or Pulse Reset Time (PRT): It is the time interval between two
pulses. It is expressed in milli seconds.
Pulse Reset Time (PRT) = Pulse Repetetion Time (PRT) – Pulse Width (PW)
60
Pulse Repetetion Frequency (PRF): It is the number of pulses transmitted per second. It
is equal to the reciprocal of pulse repetition time. It is measured in hertzs.
PRF = 1/PRT
Pulse Repetetion Time (PRT): It is the time interval between the start of one pulse and the
start of next pulse. It is the sum of pulse width and pulse reset time (PRT). In other words it
is the time. It is measured in microseconds.
PRT = PW+PRT
61
Duty Cycle (Dc): It is the ratio of average power to the peak power. It is also defined as the
produt of pulse width and PRF. It has no units.
Duty Cycle, Dc = PW×PRF = PW/PRT = Pavg/Ppeak
Average Power (Pavg): It is the average transmitted power over the pulse repetition
period. ppeak
pavg
Two-Dimentional Radars: These are the radars which determine:
Range
Bearing of targets
Three-Dimentional Radars: These are the radars which determine:
Altitude
Range
Bearing of object
62
Target resolution of Radar: It is the ability of Radar to distinguish targets that are very
close in either range or bearing.
Navigational Radars: They are similar to search radars. They basically transmit short waves
which can be reflected from earth, stones and other obstacles. These are either ship borne or
airborne.
Weather Radars: These are similar to search radars. They radiate EM waves with circular
polarization or horizontal or vertical polarization.
Radar Altimeter: It is radar which is used to determine the height of the aircraft from the
ground.
Air Traffic Control Radars: This consists of primary and secondary radars to control the
traffic in air.
63
Primary Radars: It is radar which receives all types of echoes including clouds and aircrafts. It
receives its own signals as echoes.
Secondary Radars: It transmits the pulses and receives digital data coming from aircraft
transponder. The data like altitude, call signs interms of codes are transmitted by the
transponders. In military applications, these transponders are used to establish flight identity
etc. Example of secondary radar is IFF radar.
Pulsed Radar: It is radar which transmits high power and frequency pulse. After transmitting
one pulse, it receives echoes and then transmits another pulse. It determines direction, distance
and altitude of an object.
CW Radar: It is radar which transmits high frequency signal continuously. The echo is a
received and processed.
Un modulated CW Radar: It is radar in which the transmitted signal has constant

amplitude and frequency. It useful to measure velocity of the object but not the speed.
Modulated CW Radar: It is radar in which the transmitted signal has constant amplitude
with modulated frequency.
MTI Radar: It is pulsed radar which uses the Doppler frequency shift for discriminating
moving targets from fixed ones, appearing as clutter.
Local Oscillator: It is an oscillator which generates a frequency signal which is used to

convert the received signal frequency into a fixed intermediate frequency.
Mixer: It is a unit which mixes or heterodynes the frequency of the received echo signal
and the frequency of local oscillator and then produces a signal of fixed frequency
known as intermediate frequency. This unit is useful to increase the signal-to-noise ratio.
Doppler Frequency: Is the change in the frequency of a signal that occurs when the source
and the observer are in relative motion, or when the signal is reflected by a moving object,
there is an increase in frequency as the source and the observer ( or the reflecting object )
approach, and a decrease in frequency as they separate
Doppler Effect: Doppler Effect is discovered by Doppler. It is a shift in frequency and the
wavelength of the wave as perceived by the source when the source or the target is in motion.
Astronomy Radar: It is radar which is used to probe the celestial objects.
OTH Radar: It represents Over-The-Horizon radar. It is radar which can look beyond the
radio horizon. It uses ground wave and sky wave propagation modes between 2MHz and
30MHz.
MST Radar: It represents Mesosphere, Stratosphere and Troposphere radar. Mesosphere

exists between 50km and 100km above the earth. Stratosphere exits between 10km and 50 km
above the earth. Troposphere exists between 0 and 10km above the earth. MST Radar is used
to observe wind velocity, turbulence etc.
PPI: It represents Plan position Indicator. It is a circular display with an intensity

modulated map. It gives the location of a target in polar coordinates.
A-Scope: It is a radar display and represents an oscilloscope. Its horizontal coordinate

represents the range and its vertical coordinate represents the target echo amplitude. It is the
most popular radar display.
B-Scope: It is a radar display and it is an intensity modulated radar display. Its horizontal axis
represents azimuth angle and its vertical axis represents the range of the target. The lower
edge of the display represents the radar location.
Tracking Radar: It is radar which tracks the target and it is usually ground borne. It provides
range tracking and angle tracking. It follows the motion of a target in azimuth and elevation.
Monostatic Radar: It is radar which contains transmitter and receiver at the same location
with common antenna.
Bistatic Radar: In this radar transmitting and receiving antennas are located at different
locations. The receiver receives the signals both from the transmitter and the target.
Laser Radar: It is radar which uses laser beam instead of microwave beam. Its frequency of
operation is in between 30 THz and 300 THz.
Remote Sensing Radar: It provides the data about the remote places and uses the shaped
beam antenna. The angle subtended at the radar antenna is much smaller than the angular
width of the antenna beam.
Phased Array Radar: It is radar which uses phased array antenna in which the beam is
scanned by changing the phase distribution of array. It is possible to scan the beam with
this radar at a fraction of microseconds.
Clutter: The clutter is an unwanted echo from the objects other than the
targets.
LIDAR: It represents Light Detection and Ranging. it is sometimes called as LADAR or Laser
Radar.
Pulse Doppler radar: It is radar that uses series of pulses to obtain velocity content.
Radar Signature: It is the identification of patterns in a target radar cross-section.
Range Tracking Radar: It is radar which tracks the targets in range.
TWS Radar: It represents Tract-While-Scan Radar. This radar scans and tracks the targets
simultaneously.
Blind Range: is a range corresponding to the time delay of an integral multiple of the inter
pulse period plus a time less than or equal to the transmitted pulse length. Radar usually
cannot detect targets at a blind range because of interference by subsequent transmitted
pulses. The problem of blind ranges can be solved or largely mitigated by employing multiple
PRFs.
Radar Display:
A radar display is an electronic instrument for visual representation of radar data. Radar
displays can be classified from the standpoint of their functions, the physical principles of their
implementation, type of information displayed, and so forth. From the viewpoint of
function, they can be detection displays, measurement displays, or special displays. From the
viewpoint of number of displayed coordinates, they can be one dimensional (1D), two
dimensional (2D), or three dimensional (3D).
37
An example of a 1D display is the range display (A-scope). Most widely used are 2D
displays, represented by the altitude range display (range-height indicator, or RHI), azimuth
elevation display (C-scope), azimuth range display (B-scope), elevation range display (E-
scope), and plan position indicator ( PPI ). These letter descriptions date back to World War II,
and many of them are obsolete. From the viewpoint of physical implementation, active and
passive displays are distinguished. The former are represented mainly by cathode ray tube (CRT)
displays and semiconductor displays. Passive displays can be of liquid crystal or ferroelectric
types. In most radar applications CRT displays remain the best choice because of their good
performance and low cost.
From the viewpoint of displayed information, displays can be classified as presenting radar
signal data, alpha numeric’s, or combined displays. These can be driven by analog data
(analog or raw video displays) or digital data (digital or synthetic video displays). Displays in
modern radar are typically synthetic video combined displays, often using the monitors of
computer
based work stations.
Now we will discuss the classifications of radar display from this figure.
38
39
OBJECTIVE TYPE QUESTIONS
1.The Doppler shift Df is given by { ]
a. 2Vr / k b. Vr / 2 k c. 2k / Vr d. k/ Vr
2. Magnetrons are commonly sued as radar transmitters because [ ]
a. high power can be generated and transmitted to aerial directly from oscillator
b. it is easily cooled c. it is a cumbersome device d. it has

least distortion.
3. A simple CW radar does not give range information because [ ]
a. it uses the principle of Doppler shift
b. continuous echo cannot be associated with any specific part of the transmitted
wave c. CW wave do not reflect from a target d. multi echoes distort the
information
4. Increasing the pulse width in a pulse radar - [ ]
73
a. increases resolution b. decreases resolution
c. has no effect on resolution d. increase the power gain
5. COHO in MTI radar operates ------- [ ]
a. at supply frequency b. at intermediate

frequency c. pulse repetition frequency d. station
frequency.
6. A high noise figure in a receiver means [ ]
a. poor minimum detectable signal b. good detectable

signal c. receiver bandwidth is reduced d. high power
loss.
7. Which of the following will be the best scanning system for tracking after a target has
been
acquired [ ]
a. Conical b. Spiral c. Helical d. Nodding
40
74
8. A RADAR IS used for measuring the height of an aircraft is known as _ [ ]
a. radar altimeter b. radar elevator c. radar speedometer d.

radar
latitude
9. VOR stands for [ ]
a. VHF omni range b. visually operated radar
c. voltage output of regulator. d. visual optical radar
10. The COHO in MTI radar operates at the [ ]
a. received frequency b. pulse repetition frequency
c. transmitted frequency d. intermediate frequency.
11. Radar transmits pulsed electromagnetic energy because [ ]
75
a. it is easy to measure the direction of the

target. b. it provides a very ready
measure*ment of range
c. it is very easy to identify the targets d. it is easy to measure the velocity of

target
12. A scope displays [ ]
a. neither target range nor position, but only target velocity.
b. the target position, but not range c. the target position and
range d. the target range but not position.
13. Which of the following is the remedy for blind speed problem [ ]
a. change in Doppler frequency b. use of MTI
c. use of Monopulse d. variation of PRF.
14. Which of the following statement is incorrect? Flat topped rectangular pulses
must be
transmitted in radar to [ ]
76
a. allow accurate range measurements b. allow a good minimum

range. c. prevent frequency changes in the magnetron.
d. make the returned echoes easier to distinguish from noise.
41
15. In case the cross section of a target is changing, the tracking is generally done by [ ]
a. duplex switching b. duplex scanning c. mono pulse d. cw

radar
16. Which of the following is the biggest disadvantage of the CW Doppler radar ? [ ]
a. it does not give the target velocity b. it does not give the target
position c. a transponder is required at the target d. it does not give the
target range.
17. The sensitivity of a radar receiver is ultimately set by [ ]
a. high S/N ratio b. lower limit of signal input
c. over all noise temperature d. higher figure of merit
77
18. A rectangular wave guide behaves like a [ ]
a. band pass filter b. high pass filter
c. low pass filter d. m - derived filter
19. Non linearity in display sweep circuit results in [ ]
a. accuracy in range b. deflection of focus
c. loss of time base trace. d. undamped indications
20. The function of the quartz delay line in a MTI radar is to [ ]
a. help in subtracting a complete scan from the previous scan
b. match the phase of the Coho and the output

oscillator. c. match the phase of the Coho and the
stalo
d. delay a sweep so that the next sweep can be subtracted from it,
78
Answers:
1.a 2.a 3.b 4.b 5.b 6.a 7.a 8.a 9.a 10.d
11.b 12.d 13.d 14.d 15.c 16.d 17.c 18.b 19.a 20.a
ESSAY TYPE QUESTIONS
1. Discuss the parameters on which maximum detectable range of a radar system

depends.
2. What are the specific bands assigned by the ITU for the radar? What the
corresponding frequencies?
3. What are the different range frequencies that radar can operate and give their
applications?
4. What are the basic functions of radar? In indicating the position of a target,
what is the difference between azimuth and elevation?
5. Derive fundamental radar range equation governed by minimum receivable
echo power smin.
6. Modify the range equation for an antenna with a transmitting gain G and
operating at a wavelength.
7. Draw the functional block diagram of simple pulse radar and explain the
purpose and functioning of each block in it.
8. List major applications of radar in civil and military systems.
9. With the help of a suitable block diagram explain the operation of a pulse radar
10. Explain how the Radar is used to measure the range of a target?
79
11. Draw the block diagram of the pulse radar and explain the function of each block
12. Explain how the Radar is used to measure the direction and position of target?
13. What are the peak power and duty cycle of a radar whose average transmitter
power is 200W, pulse width of 1µs and a pulse repetition frequency of 1000Hz?
14. What is the different range of frequencies that radar can operate and
give their applications?
15. What are the basic functions of radar? In indicating the position of a target,
what is the difference between azimuth and elevation?
16. Determine the probability of detection of the Radar for a process of threshold
17. Draw the block diagram of Basic radar and explain how it works?
18. Write the simplifier version of radar range equation and explain how this
equation does not adequately describe the performance of practical radar?
19. Derive the simple form of the Radar equation.
20. Compute the maximum detectable range of a radar system specified below:
a. Operating wavelength = 3.2 cm
b. Peak pulse transmitted power = 500

kW. c. Minimum detectable power =
10-3 W
c. Capture area of the antenna = 5 sq.m.
d. e. Radar cross-sectional area of the targe t = 20 sq.m.
80

Radar Systems: Lecture Notes ON

Uploaded by

Copyright:

Available Formats

Radar Systems: Lecture Notes ON

Uploaded by

Document Information

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Radar Systems: Lecture Notes ON

Uploaded by

Copyright:

Available Formats

Smartzworld.com Smartworld.

IV B.Tech II semester (JNTUH-R13)

ELECTRONICS AND COMMUNICATION ENGINEERING

The name Radar stands for Radio Detection and Ranging

Two distinguishing characteristics:

(1 mm < l < 75 cm)

2. Active technique: radiation is emitted by radar – radiation scattered by objects is

Radar is an electromagnetic system for the detection and location of

Energy detecting receiver and a processor.

A portion of the transmitted signal is intercepted by a reflecting object (target) and is

RADAR RANGE MEASUREMENT

where c = eed of light

= round trip time

The simplest radar waveform is a train of narrow (0.1μs to 10μs) rectangular

Since radio waves travel at the speed of light (v = c = 300,000

The range or distance, R = cTR/2

R (in km) = 0.15TR (μs) ; R (in nmi) = 0.081TR (μs)

 1 nmi = 6076 feet =1852 meters.

Electromagnetic energy travels through air at approximately the speed of light:-

1. 300,000 kilometers per second.

2. 186,000 statute miles per second.

3. 162,000 nautical miles per second.

RUNAMBIG = c/2f P Where fP is the PRF in Hz.

Note: unmodulated CW waveforms do not permit the measurement of range.

What is done by Radar?

Radar can see the objects in

stationary or moving and

Good or bad weather.

INFORMATION GIVEN BY THE RADAR:

Radar gives the following information:

 The position of the object

NATURE AND TYPES OF RADARS:

The common types of radars

 Speed trap Radars

 Missile tracking Radars

 Early warning Radars

 Airport control Radars

 Ground mapping Radars

 Weather forecast Radars

 Gun fire control Radars

 Remote sensing Radars

 IFF (Identification Friend or Foe)

 Synthetic aperture Radars

 Missile control Radars

 MTI (Moving Target Indication) Radars

 Mesosphere, Stratosphere and Troposphere (MST) Radars

 Over-The-Horizon (OTH) Radars

 Mono pulse Radars

 Phased array Radars

 Gun direction Radars

 Airborne weather Radars

PULSE CHARACTERISTICS OF RADAR SYSTEMS:

Pulse Repetition Frequency (PRF)

Carrier is usually modulated to allow the system to capture the required

In pulse modulation, the carrier is simply switched ON & OFF in synchronization.

Pulse Reset Time = Pulse Repetition Time – Pulse Width

Unambiguous Range and is given by

c = velocity of propagation Where, TP = fP

fP is the PRF(PULSE REPETITION FREQUENCY) in Hz