Radar by abhishek mahajan

SHREEJEE INSTITUTE OF
TECHNOLOGY AND MANAGEMENT
Radar
• Guided By:- Mr. Prakash
Singh Panwar
• By:- Abhishek Mahajan
• EC BRANCH 1ST YEAR

Fundamental Principle
of Radar
RADAR- derived from the phrase RADIO
DETECTION AND RANGING.
A short burst of electro magnetic energy transmitted
and hit to an object and then return, since the velocity
of the propagation is known it would be easy to
calculate because the distance to the object as long as
it can measure time from which the transmission
started until the echo return.

of Radar

of Radar
On Board Ship the RADAR has two main tasks:
To function as an aid to prevent collision, as
with the help of RADAR one can “SEE” in fog
and darkness.
• To assist in navigation, particularly at landfalls
and when navigating in coastal waters.

Characteristics of Radar Sets and
Factors Affecting Performances
RADIO WAVES are Electro magnetic Waves
motion consist of crest and trough.

• Wavelength- is a distance between a
successive crest of waves, electromagnetic
waves of a length between 0.1-30000 mm are
known as radio waves.
• Frequency- are other way of measure of
waves motion, which indicates the number of
crest that pass a fix of initial time.
• Frequency and Wavelength are two terms
closely associated.

LOW FREQUENCY HIGH FREQUENCY

• Each type has their advantages and
disadvantages. For example a short wave
length is preferred in shipboard radar system
because there Is a relationship between the
size of the antenna and the Horizontal Beam
width, the larger width of the scanner the
smaller is the angular beam width for the
same wavelength

• Most marine radar transmit is:
• X Band (3 cm) - 9000 MHZ
• C Band (5 cm) - 5000 MHZ
• S Band (10 cm) - 3000 MHZ
LOW FREQUENCY HIGH FREQUENCY

Marine Radar Component
• a
ANTENNA
TRANSCEIVER TRANSMITTER
MAGNETRON
MODULATOR
TRIGGER
POWER
TRANSFORMER
DISPLAY
RECEIVER
MIXER
1ST AMPLIFIER
EQUALIZER
VIDEO AMPLIFIER
RADAR BLOCK DIAGRAM

RADAR ANTENNA
Transmit and receive in an concentrated beam
and a motor turns the antenna in rotation, the
signal, which are amplified the signal becomes
visible to the operator in form of a radar
picture.

Two types of RADAR ANTENNA:
SLOTTED WAVE GUIDE TYPE

• Two types of RADAR ANTENNA:
PARABOLIC TYPE

RECEIVER
The incoming signal is fed to a series of
amplifier and further to detect or
demodulator for which smooth the signal, the
main task of the receiver is to amplify the
reflected (incoming echoes) weak echoes and
make them suitable for transmission to the
indicator.

TRANSMITTER
It is the trigger pulses to the modulator and
converted the inputs into a high frequency
oscillation thru magnetron. A high frequency
oscillation are fed via wave guide or into a
coaxial cable to the transmitter/receiver
switch.

DISPLAY
A radar echoes are display in a cathode ray
tube (CRT). Several types of CRT are utilized
like A-SCAN or Short Persistent Tube, Plan
Position Indicator or PPI, Raster Scan Display.
A-SCAN or short persistent tube, the strength
of an echo derived from its amplitude.

• P.P.I DISPLAY

DISPLAY
PPI is a long persistent tube, the trace is
rotated around in unison with the rotation of
the scanner and echoes previously recorded
are retained during a period of at least one
scanner revolution.

DISPLAY
RASTER SCAN DISPLAY. Normally a rectangular
screen with dimension in the ratio 4:3 consisting
of; example 1024 horizontal lines and 1280
vertical line or picture elements (pixel)
The radar provides all echoes information in
Cartesian form (i.e. range, bearing). Before the
information can be displayed the information
must be recalculated into X-Y coordinated by a
processor.

RASTER SCAN DISPLAY

DISPLAY
The advantage of raster scan is that, it can be
viewed in daylight without a visor, and the
capacity for the additional graphic information
is almost unlimited compared with the PPI.
The disadvantage of the raster scan is that
even the best raster scan display available
today, cannot match the resolution of the old
PPI.

Factors External to the Radar Set
Affecting Detection
RADAR SCAN & RADAR SWEEP
Radar Scan- it is a one complete 360 degrees
rotation of the antenna (during one scan
normally thousand sweeps are generated and
transmitted)
Radar Sweep- is the transmission of one radar
pulse only.

Affecting Detection
PULSE REPETITION FREQUENCY (PRF)
Define as the number of pulses transmitted
per second.
Long pulse is equals to low PRF
Short pulse equals to high PRF
LONG PULSE- means more power and longer
range but less resolution in range.
SHORT PULSE- means a weaker pulse, less
radar range but better resolution in range.

Affecting Detection
RADAR RANGE DEPEND MAINLY IN DIFFERENT
PARAMETERS
Vertical Beam Width
Selected Pulse Length
Height of Antenna
Installation of Antenna
Ship’s Trim

Safe Distance
IMPORTANT RADAR RANGE PARAMETERS
Antenna Height
Height of the Target
Size of the Target
Target Reflecting Area
Materials of the Target
Shape of the Target
Weather Condition

Safe Distance
FOLLOWING PARAMETERS MUST TAKEN INTO
ACCOUNT:
Transmitted Peak Power
Wavelength
Pulse Length
Antenna Gain
Noise Figure
Number of Pulses Per Scan
Wave Guide Loss
Display Parameters

Safe Distance
RANGE DISCRIMINATION
The ability of radar to discriminate between
two small object close together in the same
bearing.
Effecting range discrimination are:
Select Pulse Length
The size of the spot
If possible short pulse and short range should be selected and
focused, brightness carefully adjusted.

Safe Distance
BEARING DISCRIMINATION
The ability of radar to discriminate between
two small object close together at the same
range but different bearing.
Bearing discrimination depends on:
Horizontal Beam Width
The spot size
Correct focusing and brightness setting will
improve the bearing discrimination.

Safe Distance
BEARING AND RANGE DISTORTION
The radar’s possibility to reproduce on area or
a ship correctly and to discriminate between
close lying targets is limited and varies with
different types of radar.
The discriminating ability in range is usually
25-75 meters, however the accuracy is lower
on long range.

Safe Distance
BEARING AND RANGE DISTORTION
The discriminating ability laterally is usually 1-
2 degrees.
Radar sets with a wavelength of 3 cm have a
better discriminating ability compared with
the 1 cm wavelength.

Radiation Hazards and
Precaution
MAGNETIC COMPASS
The magnetic compass must have a safe
distance from the radar. Nowadays, although
most ships are equipped with zero compass,
the magnetic compass is still the master
compass on all ships and thus should be taken
good care of.
Normally the safe distance varies between 1
and 5 meters.

Precaution
RADIATION
Marine radar transmits energy of varying strength
in form of short pulses or bursts. Pulse power can
produce biological changes not obtained with
constant wave transmission. At short distance,
transmission from marine radars may pose a
health hazard, follow the instruction from the
radar manufacturer closely and don’t take any
chances.

Precaution
RADIATION
When working close to a radar antenna, make
sure that a warning signal has been placed on
the radar console. Clearly telling everybody
that no start up should be attempted before
the work on the antenna is completed or
cancelled.

Precaution
RADIATION
Whenever the air humidity is abnormally high
which it is in fog, rain, snow and hale, a reduction
in radar detection range should be expected.
Some disturbances of radar picture:
Sea
Rain
These disturbances maybe serious so refer to the
radar manual for more details.

Precaution
NORMAL TRANSMISSION OF RADAR WAVES
Radar conditions at approximately 10-15%
greater that the distance to the optical horizon
said to have normal transmission of radar waves.
Generally, normal conditions exist in areas with
cold air masses. The longer the wavelength, the
greater is the tendency to bend round objects.
Hence you can expect the 1 cm radar to have
greater range that the 3 cm radar.

Radar by abhishek mahajan

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Radar by abhishek mahajan