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BANGLADESH
SUBMITTED BY
SHARAT CHANDRA BARMAN
ROLL NO: 0715029
REG. NO: 1075
SESSION: 2007-2008
DEPARTMENT OF APPLIED PHYSICS, ELECTRONICS &
COMMUNICATION ENGINEERING,
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ISLAMIC UNIVERSITY, KUSHTIA.
PLACE: COX’S BAZAR METEOROGICAL RADAR STATION,
BANGLADESH.
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Our major purpose of this field work is to know about –
**How a RADAR is used to detect meteorological condition of a
certain region.
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RADAR
Radar is an object-detection system which uses electromagnetic waves—specifically radio waves—
to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft,
ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish, or
antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path.
The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the
same site as the transmitter.
Radar Basic Principles
The following figure shows the operating principle of a primary radar set. The radar antenna
illuminates the target with a microwave signal, which is then reflected and picked up by a
receiving device. The electrical signal picked up by the receiving antenna is called echo or
return. The radar signal is generated by a powerful transmitter and received by a highly
sensitive receiver.
Figure 1: Block diagram of a primary radar
All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The
reflected signal is also called scattering. Backscatter is the term given to reflections in the opposite
direction to the incident rays. Radar signals can be displayed on the traditional plan position
indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the
radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of
targets.
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Finally, radar relies on its own transmissions, rather than light from the Sun or the Moon, or from
electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This
process of directing artificial radio waves towards objects is called illumination, regardless of the
fact that radio waves are completely invisible to the human eye or cameras
Components of radar:
Transmitter
The radar transmitter produces the short duration high-power RF pulses of energy that are into space
by the antenna.
Duplexer
The duplexer alternately switches the antenna between the transmitter and receiver so that only one
antenna need be used. This switching is necessary because the high-power pulses of the transmitter
would destroy the receiver if energy were allowed to enter the receiver.
Receiver
The receivers amplify and demodulate the received RF-signals. The receiver provides video signals
on the output.
Radar Antenna
The Antenna transfers the transmitter energy to signals in space with the
required distribution and efficiency. This process is applied in an identical
way on reception.
Indicator
The indicator should present to the observer a continuous, easily understandable, graphic picture of
the relative position of radar targets.
Radar equation:
The power Pr returning to the receiving antenna is given by the radar equation:
Where
* Pt = transmitter power
* Gt = gain of the transmitting antenna
* Ar = effective aperture (area) of the receiving antenna
* σ = radar cross section, or scattering co-efficient, of the target
* F = pattern propagation factor
* Rt = distance from the transmitter to the target
* Rr = distance from the target to the receiver.
In the common case where the transmitter and the receiver are at the same location, Rt = Rr and the
term Rt² Rr² can be replaced by R4, where R is the range.
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These yields:
This shows that the received power declines as the fourth power of the range, which means that the
reflected power from distant targets is very, very small.
The equation above with F = 1 is a simplification for vacuum without interference. The propagation
factor accounts for the effects of multipath and shadowing and depends on the details of the
environment. In a real-world situation, pathloss effects should also be considered.
Doppler effect
Ground-based radar systems used for detecting speeds rely on the Doppler effect. The apparent
frequency (f) of the wave changes with the relative position of the target. The doppler equation is
stated as follows for vobs (the radial speed of the observer) and vs (the radial speed of the target) and
f0 frequency of wave :
However, the change in phase of the return signal is often used instead of the change in frequency. It
is to be noted that only the radial component of the speed is available. Hence when a target is
moving at right angle to the radar beam, it has no velocity while one parallel to it has maximum
recorded speed even if both might have the same real absolute motion.
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Radar signal processing
Types of scan
* Primary Scan: A scanning technique where the main antenna aerial is moved to produce a scanning
beam, examples include circular scan, sector scan etc.
* Secondary Scan: A scanning technique where the antenna feed is moved to produce a scanning
beam, examples include conical scan, unidirectional sector scan, lobe switching etc.
* Palmer Scan: A scanning technique that produces a scanning beam by moving the main antenna
and its feed. A Palmer Scan is a combination of a Primary Scan and a Secondary Scan.
Radar modulators:
Modulators act to provide the waveform of the RF-pulse. There are two different radar modulator
designs:
* High voltage switch for non-coherent keyed power-oscillators. These modulators consist of a high
voltage pulse generator formed from a high voltage supply, a pulse forming network, and a high
voltage switch such as a thyratron. They generate short pulses of power to feed the e.g. magnetron, a
special type of vacuum tube that converts DC (usually pulsed) into microwaves. This technology is
known as Pulsed power. In this way, the transmitted pulse of RF radiation is kept to a defined, and
usually, very short duration.
* Hybrid mixers, fed by a waveform generator and an exciter for a complex but coherent waveform.
This waveform can be generated by low power/low-voltage input signals. In this case the radar
transmitter must be a power-amplifier, e.g. a klystron tube or a solid state transmitter. In this way,
the transmitted pulse is intrapulsemodulated and the radar receiver must use pulse compression
technique mostly.
Radar wave modulation:
1. Amplitude Modulation
–
Vary the amplitude of the carrier sine wave
2. Frequency Modulation
–
Vary the frequency of the carrier sine wave
3. Pulse-Amplitude Modulation
–
Vary the amplitude of the pulse
4. Pulse-Frequency Modulation
–
Vary the Frequency at which the pulses occur
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Modulation
Radar Jamming:
Radar jamming refers to radio frequency signals originating from sources outside the radar,
transmitting in the radar's frequency and thereby masking targets of interest. Jamming may be
intentional, as with an electronic warfare (EW) tactic, or unintentional, as with friendly forces
operating equipment that transmits using the same frequency range. Jamming is considered an active
interference source, since it is initiated by elements outside the radar and in general unrelated to the
radar signals.
Signal Reception
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Only a minute portion of the
RF is reflected off the target.
Only a fraction of that returns
to the antenna.
The weaker the signal that
the receiver can process, the
greater the effective range .
Plot and track extraction
Radar video returns on aircraft can be subjected to a plot extraction process whereby spurious and
interfering signals are discarded. A sequence of target returns can be monitored through a device
known as a plot extractor. The non relevant real time returns can be removed from the displayed
information and a single plot displayed. In some radar systems, or alternatively in the command and
control system to which the radar is connected, a radar tracker is used to associate the sequence of
plots belonging to individual targets and estimate the targets' headings and speeds.
Antenna used for Two Basic Purposes:
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1. Radiates RF Energy
2. Provides Beam Forming and Focus
* Must Be 1/2 of the Wave Length for the maximum wave length employed
* Wide Beam pattern for Search, Narrow for Track
Beam width Vs. Accuracy:
Beamwidth vs Accuracy
Azimuth Angular Measurement:
Azimuth Angular Measurement
Relative Bearing = Angle from ship’s heading.
True Bearing = Ship’s Heading + Relative Bearing
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Ship’s Heading
Angle
Target Angle
Determining Altitude:
Concentrating Radar Energy Through Beam Formation:
Ship A
Ship B
Linear Arrays:
*Uses the Principle of wave summation (constructive interference) in a special direction and wave
cancellation (destructive interference) in other directions.
*Made up of two or more simple half-wave antennas.
Quasi-optical:
*Uses reflectors and “lenses” to shape the beam.
Wave Guides:
*Used as a medium for high energy shielding.
*Uses A Magnetic Field to keep the energy centered in the wave guide.
*Filled with an inert gas to prevent arcing due to high voltages within the waveguide.
Two Basic Radar Types:
1. Pulse Transmission.
2. Continuous Wave.
Specific Types of Radar:
1.Frequency Modulated CW Radar
*Use for radar altimeters and missile guidance.
2.Pulse Doppler
*Carrier wave frequency within pulse is compared with a reference signal to
detect moving targets.
3.Moving Target Indicator (MTI) System
*Signals compared with previous return to enhance moving targets. (search radars)
4.Frequency Agile Systems
* Difficult to jam
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Waves and Frequency Ranges:
The spectrum of the electric magnetic waves shows frequencies up to 1024 Hz. This very large
complete range is subdivided because of different physical qualities in different subranges.An
overview shows the following figure:
Figure 4: Waves and frequency ranges used by radar.
Since without that the correct frequency is known, a transformation isn't always possible into the
new wavebands-
A- and B- Band (HF- und VHF- Radar)
These radar bands below 300 MHz have a long historically tradition because these frequencies
represented the frontier of radio technology at the time during the
C- Band (UHF- Radar)
There are some specialized Radar sets developed for this frequency band (300 MHz to1 GHz). It is a
good frequency for the operation of radars for the detection and tracking of satellites and ballistic
missiles over a long range. These radars operate for early warning and target acquisition like the
surveillance radar for the Medium Extended Air Defense System (MEADS)
D- Band (L-Band Radar)
This frequency band (1 to 2 GHz) is preferred for the operation of long-range air-surveillance radars
out to 250 NM (≈400 km). They transmit pulses with high power, broad bandwidth and an intrapulse
modulation often.
E/F-Band (S-Band Radar)
The atmospheric attenuation is higher than in D-Band. Radar sets need a considerably higher
transmitting power than in lower frequency ranges to achieve a good maximum range. As example
given the Medium Power Radar (MPR) with a pulse power of up to 20 MW
G- Band (C-Band Radar)
In G- Band there are many mobile military battlefield surveillance, missile-control and ground
surveillance radar sets with short or medium range.
I/J- Band (X- and Ku- Band Radars)
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In this frequency-band (8 to 12 GHz) the relationship between used wave length and size of the
antenna is considerably better than in lower frequency-bands.
K- Band (K- and Ka- Band Radars)
The higher the frequency, the higher is the atmospheric absorption and attenuation of the waves.
Otherwise the achievable accuracy and the range resolution rise too.
V-Band
By the molecular dispersion (here this is the influence of the air humidity), this frequency band stay
for a high attenuation. Radar applications are limited for a short range of a couple of meters here.
W-Band
Here are two phenomena visible: a maximum of attenuation at about 75 GHz and a relative
.
Pulse transmission radar:
minimum at about 96 GHz
1. Pulse transmission.
Range vs. Power/PW/PRF
* Minimum Range: If still transmitting when return
received

→
RETURN NOT SEEN.
Max Range:
AveragePower
PeakPower
As
PW ↑
PRF ↑

PW
PRT
min Rh
↓
↔
 PW *PRF
max Rh
↑
↓
2. Pulse repetition frequency (PRF)
a. Pulses per second
b. Relation to pulse repetition time (PRT)
c. Effects of varying PRF
(1) Maximum range (2) Accuracy
3. Peak power
a. Maximum signal power of any pulse
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b. Affects maximum range of radar
4. Average power
a. Total power transmitted per unit of time
b. Relationship of average power to PW and PRT
5. Duty cycle
a. Ratio PW (time transmitting) to PRT (time of entire cycle, time transmitting plus rest time)
b. Also equal to ratio of average power to peak power
Determining Range with Pulse Radar
Range 
c*t
2
c = 3 x 108 m/sec
t is time to receive return divided by 2 because pulse traveled to object and back
* Pulse Width (PW)
a. Length or duration of a given pulse
* Pulse Repetition Time (PRT=1/PRF)
a. PRT is time from beginning of one pulse to the beginning of the next
b. PRF is frequency at which consecutive pulses are transmitted.
* PW can determine the radar’s minimum detection range.
* PRF can determine the radar’s maximum detection range.
*Describe the components of a pulse radar system.
(1)Synchronizer (2)Transmitter (3)Antenna (4)Duplexer (5)Receiver (6)Display unit (7)Power supply
Block diagram of pulse radar:
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Pulse radar block diagram
Synchronizer
Transmitter
RF
Power
Supply
Duplexer
(Switching Unit)
Echo
Display
ATR
antenna
TR
Receiver
Video
Antenna Bearing or Elevation
Continuous Wave Radar
1. Employs continual RADAR transmission
2. Separate transmits and receives antennas
3. Relies on the “DOPPLER SHIFT”
Doppler Frequency Shifts
Motion Away:
Echo Frequency Decreases
Motion Towards:
Echo Frequency Increases
Continuous Wave Radar Components
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antenna
CW
RF
OUT
OSCILLITOR
MIXER
DIOSCRIMINATOR
IN
amp
antenna
INDICATOR
Pulse Vs Continuous Wave:
Pulse echo
1.Single antenna
2.Gives range usually Alt. as well.
3.susceptibility to jamming.
4.physical range determined by PW
and PRP .
Continuous wave
1.requires 2 antennas.
2.range or Alt. Info.
3.high SNR.
4.More difficult to jam but easily deceived.
5.Amp can’t be tuned to look for expected
Frequencies.
Applications of Radar
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To detect various weather condition.
In commercial airliners.
In ground controlled control system.
 To determine the fix position, distance and map geographical areas, at seas.
 Satellite and other communications
 Military operations, etc.
We observed in Cox’s bazaar Meteorological RADAR station Doppler pulse RADAR is used.
We observed there are five rooms these are:
1. Electricity Room.
2. Data analysis Room.
3. Observation Room.
4. Storage Room.
5. Radar Equipment Room.
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6. Maintenance Room.
According to the addressed of RADAR engineer Mr. Md. Abdul Mumin, its basic components are:
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Magnetron or klystron type oscillator is used to generate microwaves.
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Rectangular wave guide is used to feed the signal to the antenna to be transmitted.
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When these signal is reflected by rain bearing cloud (RBC), and received by the antenna
these signal is automatically analyzed using Linux Operating system as shown in fig-6.
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Its range is 440Km and for out of this range satellite is used.
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These analyzed data are internally sent to Dhaka Met office from where weather related
news is telecasted.
Fig-6:Cox's Bazar Radar Image
Enjoying this industrial tour we have come to learn about the system of meteorological radar station
and got an idea about the equipments of it. We also learnt about waveguide and its communication
techniques. The total system is very complicated & secured. We also realized a concept about the
engineer’s role in this organization.
We thank our teachers so much for giving the opportunity to enjoy the sea-beach of Cox’s bazar,
Saintmartin-Island beside our study tour.
We also thank all my friends especially those who served cordially to present a wonderful tour.
We have made this report from our knowledge & experience throughout this tour and hope that this
report will be meaningful and effective. We beg apology for the unavoidable mistake that might
happen in this report. Thankfully……………….
3rd year students,
Dept. of Applied Physics, Electronics and Communication Engineering.
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Designed by Bhajan Saha
& SHARAT
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