slide 1: Seminar Report Military Radar System
CONTENTS
1. ABSTRACT
2. MILITARY RADAR SYSTEM
i INTRODUCTION
ii BASIC PRINCIPLE OF RADAR
iii SYSTEM CONFIGURATION
iv SETS OF TERMINAL EQIPMENTS
v FUNCTIONAL DESCRIPTION OF RADAR SUBSYSTEM
3. APPLICATIONS OF RADAR IN MILITARY
4. CONCLUSION
5. REFERENCES
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ABSTRACT
RADAR Radio Detection and Ranging is basically a means of gathering
information about distant objects by transmitting electromagnetic waves at them and
analyzing the echoes. Radar finds a number of applications such as in airport traffic control
military purposes coastal navigation meteorology and mapping etc. Military radars have a
highly specialized design to be highly mobile and easily transportable by air as well as
ground.
This report discusses about the military radar system. Radar system uses the
general antenna properties. Radar is used in early warning altering along with weapon control
functions. This report gives the view of configuration of a typical military radar data flow in
a typical radar system operating the radar system functions various terminal equipments
used along with their functions functional description of radar subsystem some of the
important parts of the radar such as transmitter unit receiver unit antenna AFC Automatic
Frequency Control etc. advanced features of the radar advantages and limitations of the
military radar system. This report also describes the target tracking firing control weapon
aiming process using military radar.
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INTRODUCTION
Radar is an acronym for Radio Detection And Ranging. A radar is an electro-magnetic
device capable of transmitting a electro-magnetic wave near 1-110 Ghz receives back a
reflection from a target and based on the characteristics of the returned signal determine things
about the target.
Radar is an electromagnetic system for the detction and location of reflecting objects
such as aircraft ship spacecraft vehicles people and the natural environment. it operates by
radiating energy into space and detecting the echo signal reflected from an object or target.
The reflected energy that is returned to the radar not only indicates the presence of a target but
by comparing the received echo signal with the signal that was transmitted its location can be
deterined along with othertarget –related information. Radar can perform its function at long
or short distences and under the conditions impervious to optical and infrared sensors. It can
operate in darkness haze fog rain and snow. Its ability to measure distance with very high
accuracy and in all wheather is on of its most important attributes.
RADAR Radio Detection and Ranging is basically a means of gathering
information about distant objects. Radar has been employed on the ground in air on the sea
and in space. Radar finds a number of applications such as in airport traffic control military
purposes coastal navigation meteorology and mapping etc. The development of the radar
technology took place during the World War II in which it was used for detecting the
approaching aircraft and then later for many other purposes which finally led to the
development of advanced military radars being used these days. Military radars have a highly
specialized design to be highly mobile and easily transportable by air as well as ground.
Military radar should be an early warning altering along with weapon control
functions. It is specially designed to be highly mobile and should be such that it can be
deployed within minutes. Military radar minimizes mutual interference of tasks of both air
defenders and friendly air space users. This will result in an increased effectiveness of the
combined combat operations. The command and control capabilities of the radar in
combination with an effective ground based air defense provide maximum operational
effectiveness with a safe efficient and flexible use of the air space. The increased operational
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effectiveness is obtained by combining the advantages of centralized air defense management
with decentralized air defense control.
BASIC PRINCIPLE OF RADAR
A transmitter generates an electromagnetic signal such as sine wave that is radiated
into the space by using an antenna. A portion of the transmitted energy is intercepted by the
target and reradiated in many directions. The reradiation directed back towards the radar is
collected by the radar antenna which delivers it to the receiver. There it is processed to detect
the presence of the target and determine is location.
Figure 1. Basic principle of radar
Range to a target
The most common radar signal or waveform is a series of short-duration somewhat
rectangular-shaped pulses modulating a sine wave carrier. “The range to a target is determined
by the time TR is takes the radar signal to travel to the target and back.”
The range to a target then
………………..1
Transmitter
Receiver
Transmitted signal
Echo signal
Range to target
Antenna
Target detection and
information extraction
R
-
2
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Here c the velocity of light 3×10
8
⁄
TR the time taken by signal to reach the target and back to radar in μ sec.
R in km i.e.
Rkm .15 T μs .………………2
Radar equation
By using the radar equation we can find range beyond which a radar cannot detect any object.
Radar equation is
√
2
4 2
4
……………3
Here Pt transmitted power by antenna
A e effective area of receiving antenna
radar cross section of the target
wavelength of transmitted signal
Smin mininum power of signal detectable to antenna.
Radar frequencies
Band designation
Nominal frequency range
L-band 1-2 GHz
S-band 2-4 GHz
C-band 4-8 GHz
X-band 8-12 GHz
Ku-band 12-18 GHz
Ka-band 27-40 GHz
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FIRST USE OF RADAR IN MILITARY
During the 1930s efforts to use radio echoes for aircraft detection were initiated
independently and almost simultaneously in eight countries that were concerned with the
prevailing military situation and that already had practical experience with radio technology.
The United States Great Britain Germany France the Soviet Union Italy the Netherlands
and Japan all began experimenting with radar within about two years of one another and
embarked with varying degrees of motivation and success on its development for military
purposes. Several of these countries had some form of operational radar equipment in military
service at the start of World War II.
The first observation of the radar effect at the U.S. Naval Research Laboratory NRL
in Washington D.C. was made in 1922. NRL researchers positioned a radio transmitter on
one shore of the Potomac River and a receiver on the other. A ship sailing on the river
unexpectedly caused fluctuations in the intensity of the received signals when it passed
between the transmitter and receiver.
The first radars developed by the U.S. Army were the SCR-268 at a frequency of 205
MHz for controlling antiaircraft gunfire and the SCR-270 at a frequency of 100 MHz for
detecting aircraft. Both of these radars were available at the start of World War II as was the
navy’s CXAM shipboard surveillance radar at a frequency of 200 MHz. It was an SCR-270
one of six available in Hawaii at the time that detected the approach of Japanese warplanes
toward Pearl Harbor near Honolulu on December 7 1941 however the significance of the
radar observations was not appreciated until bombs began to fall.
In the present time radar is an important part of air defense system as well as
operations of offensive missiles and other weapon. In air defense it performs the function of
surveillance and weapon control. The Surveillance system includes target detection target
recognition target tracking and designation to a weapon system. Weapon- control radars track
targets direct the weapon to an intercept and assess the effectiveness of the engagement
called battle damage assessment. A missile system might employ radar methods for the
guidance and fuzing of the weapon. High-resolution imaging radar such as synthetic aperture
radar has been used for the reconnaissance purposes and for detecting the fixed and moving
targets on the battlefield.
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ADVANCED FEATURES OF RADAR
Multiple target handling and engagement capability.
Short and fast reaction time between target detection and ready to fire moment.
Easy to operate and hence low manning requirements and stress reduction under
several condition.
Highly mobile system to be used in all kind of terrain.
Highly accurate angle tracking of targets.
Flexible weapon integration and unlimited number of single air defense weapons can be
provided with target data.
High resolution which gives excellent target discrimination and accurate tracking.
Radar can make in-storm measurements.
The identification of the targets as friend or hostile is supported by IFF which is an
integral part of the system. During the short time when the targets are exposed accurate
data must be obtained. A high antenna rotational speed assures early target detection and a
high data update rate required for track accuracy
The radar can use linear horizontal polarization in clear weather. During rains
to improve the suppression of rain clutter provision exists to change to circular polarization
at the touch of the button from the display console.
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THE SYSTEM CONFIGURATION
A typical military radar system can be split up into three parts:
1 Radar group
The radar group consists of antenna mast unit remote control high tension unit LO/AFC
Local Oscillator/Automatic Frequency Control unit radar transmitter radar receiver video
processor waveguide drier and IFF interrogator.
The transmitter and receiver form the active part of the system. The integrated radar/IFF
antenna is fitted on the collapsible mast mounted on the container. The container is
connected by cable to the operator/control shelter.
2 Shelter
Shelter contains display unit processor unit TV monitor colour PPI Plan Position
indicator IFF control unit air conditioner battery charger with battery Radio set with
antenna for data link radio set with antenna for voice transmission i.e. communication filter
box for radios.
3 Motor generator
The motor generator supplies power to the whole radar system.
SETS OF TERMINAL EQUIPMENT
These are the sets of lightweight man portable units which can be easily be stacked together
and consists of: -
1 TDR Target Data Receiver
The TDR is either connected to a VHF-FM radio receiver or to a LCA to receive
transmitted target data. The TDR itself is intelligent it performs parallax correction
threat evaluation and it displays the result in a threat sequence enabling the weapon
commander to make the correct decision. In the parallax correction function the target data
received in the X and Y co-ordinates is transferred into the polar co-ordinates with respect
to the entered weapon position.
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2 Radio Receiver or LCA Line Connection Adapter
A radio receiver or LCA with standard 2 wire telephone line can be used to receive
target data. In principle any VHF-FM radio receiver can be used as a part of the terminal
equipment set. In case line connection is applied no radio receiver is required. An LCA
connects the 2-wire telephone line to the TDR cable.
OPERATING THE RADAR
The operator’s main task is to watch the PPI Plan Position Indicator display which
presents only moving targets in the normal mode MTI-MODE. Detected target can be
assigned with the joystick controlled order marker to initiate target tracking. Target
tracking is started and a track marker appears over the target echo. A label is displayed near
the track marker. The system computer in the processor unit processes data on this tracked
target. When an aircraft does not respond to the IFF interrogation it is considered to be
unknown.
SYSTEM FUNCTIONS
The main task of the radar is to provide individual weapon systems after an alert with
accurate target data. Therefore the system has to perform certain functions as shown in
the following block diagram: -
Figure 2. Data flow in a typical military radar system.
Target detection
by radar
Track initiation
and
Identification
Automatic target
tracking and IFF
Status
Message
transmitted to
weapon systems
Target track data
put in encoded
message
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Detection
The detection function is supported by the search radar the MTI processor and the PPI. On
the PPI all moving targets even those flying at low radial speeds are displayed to the
operator.
PPI Plan Position Indicator:- A typical radar display for a radar is the PPI. The PPI is a
presentation that maps in polar co-ordinates the location of the target in azimuth and range.
Figure 3. Example of a PPI display
Automatic Target Tracking
After target detection a track is initiated by indicating the target video with the joystick
controlled order marker. The computer starts generating a track on the basis of the
joystick data. A target track marker is displayed on the PPI over the target echo. Search
radar information is gathered and extracted by video extractor as plots. The computer
evaluates the plot information determines the position and speed of the target and
updates the generated track.
Identification
The identification function comprises: -
1 Interrogation of a target detected
2 Decoding IFF responses
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3 Display of the decoded IFF responses on the PPI
IFF Identification Friend or Foe: The IFF interrogator sends a coded challenge in the form
of pulse pairs. The selected mode of operation determines the spacing between the pulses. A
friendly target’s IFF will automatically reply to the coded challenge with an omni-directional
transmission. It sends a different sets of pulses at a slightly different frequency than the
interrogator. The IFF interrogator receives the coded reply and process it for display.
Recognition of the target is based on PPI display. The coded reply from a friendly normally
appears as a dashed line just beyond the target pulse.
figure 4. a Pulse sent by interrogator b Reply pulse by object response
Reporting Function to External Terminal Equipment
The data of the tracked targets is automatically converted to X and Y grid co-ordinates with
respect to preset co-ordinates of the radar location. The data is included in digital data
message made up for all targets being tracked. The computer-originated message is encoded
and automatically transmitted by VHF-FM radio or by line communication.
IFF Alarm
The IFF alarm function alerts the operator that the IFF code setting has to be changed.
The valid code is displayed to the operator. The IFF codes and their validity period are
entered into the system in advance.
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TERMINAL EQUIPMENT FUNCTIONS
Figure 5. Data flow at weapon systems
Target Decoding
The target information is received and decoded. In case no or disturbed target information
is received it is indicated on the TDR.
Parallax Correction
The parallax correction function is performed by the TDR. Through this function the
target data received in the X and Y co-ordinates is transferred into polar co-ordinates
with respect to the entered weapon position.
Threat Evaluation
The data of the targets received is processed by a threat evaluation program built in to
the TDR. This program places all the targets in a sequence according to their threat priority
and displays the result azimuth angle of four most threatening targets as an engagement
advice.
Message decoded
and parallax
correction
Firing at
Target
Target tracking
fire control and
weapon aiming
Target
Selection
Threat evaluation
and display of
results as advice
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FUNCTIONAL DESCRIPTION OF RADAR SUBSYSTEM
The detection of air targets is accomplished by the search radar the video processor and the
colour PPI unit. The colour PPI unit provides the presentation of all moving targets down to
very low radial speeds on a PPI screen.
The search radar is pulse Doppler radar also called MTI radar i.e. it is capable of
distinguishing between the echo from a fixed target and that of a moving target. The echoes
from fixed target are eliminated so that the echoes from the moving targets are presented on
the screen.
The great advantage of this is that it is possible to distinguish a moving target among a large
number of fixed targets even when the echoes from these fixed targets are much stronger.
To achieve this the search radar makes use of the Doppler effect if the target having a
certain radial speed with respect to the search antenna is hit by a series of transmitter pulses
from the search radar antenna the change in range between this target and antenna is
expressed by successive echo pulses in phase shifts with respect to the phase of the
transmitter pulses.
For moving targets the phase difference from echo pulse to echo pulse is continually subject
to change whereas for fixed targets this is a constant. The distinction between the echo
signals from a fixed target and moving target is obtained by detecting the above phase
differences.
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Figure 6. block diagram of radar
TRANSMITTER UNIT
ANTENNA
VIDEO
PROCESSOR
RECEIVER UNIT
LO + AFC UNIT
Modulator
Magnetron AFC Control
Circuit
Sub-Modulator
BJD
MTI Main
Amplifier
Linear
Detector
PSD
IF
Preamplifier
Linear Main
Amplifier
Image
Rejection
Miser
COHO SSLO
AFC
Discriminator
Lock Pulse
Mixer
HT UNIT
Main Supply
High Voltage Supply
PPI
Unit
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The main units of radar subsystem are: -
1 HT Unit
The high tension unit converts the phase mains voltage into a DC supply voltage of about in
the order of KV for the transmitter unit.
2 Transmitter Unit
The transmitter unit comprises:
a Modulator
The modulator consists of the following components: -
Start Pulse Amplifier
The start pulse amplifier unit comprises: -
An amplifier which amplifies the pulses from the video processor a thyratron for
discharging the pulse-shaping network. These pulses then trigger a monostable
multivibrator.
Pulse Unit
The pulse unit comprises of pulse shaping network and pulse transformer.
The pulse discharge of the pulse- shaping network will occur only if the magnetron
impedance transformed by the pulse transformer is about equal to the characteristic
impedance of the pulse-shaping network.
The thyratron diodes ensure that the remaining negative voltage caused by the mismatch on
the pulse-forming network is directed to earth.
If the mismatch is too large capacitor is charged by the discharge current to such an
extent that relay reflection coefficient too high is activated. This relay switches off the high
voltage.
b Magnetron
The magnetron is a self-oscillating RF power generator. It is supplied by the modulator by
high voltage pulses whereupon it produces band pulses. The generated RF pulses are
applied to the receiver unit.
The PRF of the magnetron pulses is determined by the synchronization circuit in the
video processor which applies start pulses to the sub-modulator of the transmitter unit. This
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sub-modulator issues start pulses of suitable amplitude to trigger the thyratron in the
modulator. On being triggered the modulator which is supplied by the high tension unit
produces high voltage pulses.
As a magnetron is self oscillating some kind of frequency control is required.
The magnetron is provided with a tuning mechanism to adjust the oscillating
frequency between certain limits. This tuning mechanism is operated by an electric motor
being part of AFC control circuit. Together with circuits in LO+AFC unit a frequency
control loop is created thus maintaining a frequency difference i.e. the intermediate
frequency of the receiver between the output frequency of the SSLO and the magnetron
output frequency. The magnetron unit comprises a coaxial tunable magnetron servo motor
driving an adjustable plunger.
Figure 7. Transmitter Unit
AFC circuit and servo
amplifier
ARC
Sensor
Readout Module
Start Pulse
Amplifier
Pulse Unit RF Power
Sensor
Thyratron
Magnetron
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3 LO+AFC Unit
The LO+AFC unit determines the frequency of the transmitted radar pulses. It
comprises of: -
1 Lock pulse mixer
2 AFC discriminator
3 Solid State Local Oscillator SSLO
4 Coherent Oscillator COHO
The SSLO generates a very stable low power RF signal lower than the desired transmitter
frequency. This signal is split in two branches and distributed as local oscillator signal to
two mixers.
These are: -
1 Image rejection mixer in the receiver unit
2 Lock pulse mixer
The lock pulse mixer mixes the SSLO signal with a fraction of the magnetron power. The
mixer output consists of AFC lock pulse provided that the magnetron is correctly tuned.
The AFC lock pulses are applied to an AFC discriminator which checks their frequency. If
the frequency of the AFC lock pulses is unequal to IF a positive or negative control voltage
for the AFC control circuit in the transmitter unit is developed to force the magnetron
frequency to the desired value. Thus the AFC loop is closed.
The AFC lock pulses are also applied to COHO. The COHO outputs a signal with a
frequency of AFC lock pulse and is synchronized with the phase of each transmitter
pulse. In this way a phase reference signal is obtained required by the phase sensitive
detector in the receiver unit.
4 Receiver Unit
The receiver unit converts the received RF echo signals to IF level and detects the IF
signals. By detecting the IF signals in two different ways two receiver channels are obtained
called MTI channel and linear channel.
The RF signals received by radar antenna are applied to the low noise amplifier. The image
rejection mixer mixes the amplified signals with the SSLO signal to obtain an IF signal.
After amplification the IF signal is split into two branches viz. a MTI channel and a linear
channel. A fraction of amplified received signal is branched off and applied to broadband
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jamming detector BJD.
In the MTI channel the IF signal is amplified again by the MTI main amplifier and applied
to the Phase Sensitive Detector PSD. The second signal applied to the PSD is the phase
reference signal from the COHO.
The output of the PSD is the function of the phase difference between the two inputs to
the PSD. The polarity pulses indicate whether the phase difference is positive or negative.
The phase differences between the COHO signal and IF echo signals from a fixed target is
constant whereas those between the COHO signals and IF echo signals from a moving target
is subject to change.
The PSD output signal is applied to the canceller in video processor.
In the linear channel the IF signal is amplified again by the linear main amplifier and
subsequently applied to the linear detector. The linear detector output signals are passed on
to the colour PPI drive unit.
5 Antenna
The search antenna is a parabolic reflector rotating with a high speed. In the focus of the
reflector is a radiator which emits the RF pulses and which receives the RF echo pulses. In
the waveguide is the polarization shifter which causes the polarization of the RF
energy to be either horizontally or circularly.
6 Video processor
The video processor processes the MTI video from the MTI receiver channel to make the
video suitable for the presentation on the colour PPI screen.
7 Protection Units
There are some protection units such as arc sensor to protect the magnetron against arcing
and RF power sensor maintaining the RF power.
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APPLICATION OF RADAR IN MILITARY
Radar is used for the multiple target detection.
Radar is used to direct the weapon to an intercept.
High-resolution imaging radars are used to detect fixed or moving targets in the
battlefield.
Radar is used for the guidance of the missile systems.
CONCLUSION
Military radars are one of the most important requirements during the wartime which can be
used for early detection of ballistic missile and also for accurate target detection and firing.
Radar system discussed here has a built in threat evaluation program which automatically
puts the target in a threat sequence and advises the weapon crew which target can be
engaged first. Most essential the target data is available to the weapon crew in time so
they can prepare themselves to engage the ‘best’ target for their specific weapon
location.
A magnetron radar system is relatively simple and reliable. As a consequence minimum
maintenance is required and thus the system life cycle costs can be kept low.
REFERENCES
1 www.google.co.in
2 www.en.wikipedia.org
3 Merril I. Skolnik ‘Introduction to Radar System’ Tata McGRAW-HILL