MUET, SZAB Khairpur Campus
Subject: Communication System
Teacher: Engr: Toqueer Jumani
Department Of Electrical Engineering
12th Batch
Prepared by:
K 12-El 17,28,29
Outlines:
1
• Microwave Communication
2
• Radar , Working Principle
3
• Types Of Radar & Applications
Microwave Communication
What are Microwaves and what Is Microwave Communication?
Microwaves:
 Microwaves are electromagnetic waves with a frequency with
wavelengths ranging from one meter to one millimeter (frequencies
between 300 MHz and 300 GHz).
 Microwaves are ideal when large areas need to be covered and
there are no obstacles in the path.
 The prefix "micro-" in "microwave" is not meant to suggest a
wavelength in the micrometer range. It indicates that microwaves
are "small" compared to waves used in typical radio broadcasting
in that they have shorter wavelengths.
What are Microwaves and what Is Microwave Communication?
Advantages Of Microwaves :
 Because of high frequency, more data can be sent through
microwaves -> increased bandwidth, higher speeds.
 Because of their short wave length, microwaves use smaller
antennas.
 Smaller antennas produce a more focused beam which is difficult to
intercept.
Did-advantages Of Microwaves :
 They require no obstacle is present in the transmission path.
 The cost of implementing the communication infrastructure is high.
 Microwaves are susceptible to rain, snow, and electromagnetic
interference.
What are Microwaves and what Is Microwave Communication?
Microwaves Communication :
 Microwave communication is the transmission of signals via radio
using a series of microwave towers.
 Microwave communication is known as a form of "line of sight"
communication, because there must be nothing obstructing the
transmission of data between these towers for signals to be properly
sent and received.
 LoS (Line of Sight) – is a visible straight line between the sender and
the receiver.
 Microwaves, one generated, propagate in a straight line in all
directions.
 Microwaves are generated by magnetrons through vibration of
electrons
Microwaves Communication :
 Fresnel zone – is an elliptical area around the LoS between a sender
and receiver.
 Microwaves are spread into this area once are generated by an
antenna; this area should be free of any obstacles.
 There are 3 modes of propagation possible, and the mode is decided
based on distance and terrain:
RADAR
RADAR
 Radar (acronym for RAdio Detection And Ranging) is an objectdetection system that uses electromagnetic waves to determine the
range, altitude, direction, or speed of objects.
 It can be used to detect aircraft, ships, spacecraft, guided missiles,
motor vehicles, weather formations, and terrain. The radar dish or
antenna transmits pulses of radio waves or microwaves that bounce off
any object in their path.
 Radar was designed shortly before World War II. Its primary purpose
was to detect the presence of aircraft.
 A radar system usually operates in the ultra-high-frequency (UHF) or
microwave part of the radio-frequency (RF) spectrum, and is used to
detect the position and/or movement of objects.
 Radar can track storm systems, because precipitation reflects
electromagnetic fields at certain frequencies.
 It has become the primary tool for short-term weather forecasting and
watching for severe weather such as thunderstorms, tornadoes, winter
storms etc.
Components Of The Radar
Radars in their basic form have four main components:
1. A transmitter, which creates the energy pulse.
2. A transmit/receive switch that tells the antenna when to transmit and
when to receive the pulses.
3. An antenna to send these pulses out into the atmosphere and
receive the reflected pulse back.
4. A receiver, which detects, amplifies and transforms the received
signals into video format.
Components Of The Radar
TRANSMITTER:
• Generate radio waves
• Perform modulation
• Amplification to high power
RECIEVER:
• High sensitivity
• Very low noise
• Ability to discern a received signal from background noise
PROCESSING & CONTROL:
• It regulates the rate at which pulses are sent (PRF). Synchronizes the
function between Transmitter, Receiver, display, duplexer etc.
DUPLEXER:
• A switch to alternatively connect Tx and Rx to antenna. Protects
receiver from high power of transmitter during transmission it aligns to
transmitter. After pulse has been sent, it aligns antenna to receiver.
Components Of The Radar
ANTENNA:
•
Takes radar pulses from transmitter and puts into the air. Focuses energy
into the well designed beam. Antenna is of two types
1)
Physically moving
2)
Electronically steered
DISPLAY:
•
Presents received information to the operator. It is of two types
1)
PPI (Plan Position Indicator)
2)
A-scope or A-scan
Working Principle Of Radar
 A radar system has a transmitter that emits radio waves called radar
signals in predetermined directions.
 When these come into contact with an object they are usually
reflected or scattered in many directions. Radar signals are reflected
especially well by materials of considerable electrical conductivity—
especially by most metals, by seawater and by wet lands.
 The radar signals that are reflected back towards the transmitter are
the desirable ones that make radar work. If the object is moving either
toward or away from the transmitter, there is a slight equivalent change
in the frequency of the radio waves, caused by the Doppler effect.
 Reflected radar signals captured by the receiving antenna are usually
very weak, they can be strengthened by electronic amplifiers. More
sophisticated methods of signal processing are also used in order to
recover useful radar signals.
 The received signals are displayed on a display system.
 The switch is called duplexer which can control transmitting and
receiving 1000 times/second.
Working Principle Of Radar
Working Principle Of Radar
 The display is in polar coordinates. A rotating antenna transmits RF
pulses at defined intervals.
 The delay between a transmitted pulse and the echo, (or return pulse)
determines the radial position of the object for each direction on the
display. The greater the echo delay from a particular object in space, the
farther from the display center its point appears.
Types Of Radar According to it’s
working






Detection and search radars
Missile guidance systems
Air Traffic Control and navigation
Space and range instrumentation radar systems
Weather-sensing Radar systems
Radars for biological research (Radar range and wavelength can be adapted
for different surveys of bird and insect migration and daily habits.
They can have other uses too in the biological field.)
Main Types Of Radar
There are two main types of radar:
1)Primary Radar:
 Continuous wave Radar
 Pulse Radar
2)Secondary Radar:
Primary Radar
 1) CONTINUOS WAVE RADAR:
 Continuous-wave radar system is a radar system where a known stable
frequency continuous wave radio energy is transmitted and then received
from any reflecting objects. The return frequencies are shifted away from the
transmitted frequency based on the Doppler effect if they are moving.
 The main advantage of the CW radars is that they are not pulsed and simple
to manufacture.
 CW radars also have a disadvantage because they cannot measure range.
Range is normally measured by timing the delay between a pulse being sent and
received, but as CW radars are always broadcasting, there is no delay to
measure.
 CW radar can measure the instantaneous rate-of-change in the target's
range. This is accomplished by a direct measurement of the Doppler shift of the
returned signal.
 The Doppler shift is a change in the frequency of the electromagnetic wave
caused by motion of the transmitter, target or both.
Primary Radar
 1) CONTINUOS WAVE RADAR:
Primary Radar
2) PULSE RADAR:
 The PULSE radar is the more conventional radar, which transmits a burst of
radar energy and then waits for the energy (or echo) to be reflected back to
the antenna.
 After a specific period of time (depending on how far the radar is searching)
another pulse will be sent followed by another listening period. Since radar
waves travel at the speed of light, range from the return can be calculated.
BASIC PULSE RADAR TERMS:
 Pulse Duration
 Pulse Repetition Time
 Pulse Repetition Frequency
 Listening Time
Primary Radar
1) PULSE DURATION:
 The time a radar set is transmitting radio frequency (RF) energy. It is also
referred to as pulse width (PW). Pulse duration is measured in millionths of a
second or microseconds.
2) PULSE REPETITON TIME:
 This is the time required to complete one transmission cycle. It is the time
from the beginning of one radar pulse to the beginning of the next. It is the
reciprocal of our next term, Pulse Recurrence Frequency (PRF). This term
represents the period for one transmission cycle.
3) PULSE REPETITON FREQUENCY:
 The PRF equals the number of pulses per second the radar transmits. If you
want the radar to look at long ranges, a low PRF is required (this allows
time for the radar energy to be reflected by the target and to return to the
antenna before the next pulse is transmitted). For shorter ranges, a higher
PRF can be used.
4) LISTENING TIME:
 Listening time is the part of the Rest Time that the radar can receive and
process the echoes of radar returns.
Secondary Radar
 A secondary radar system is a cooperative target identification system in
which the interrogator transmits an encoded signal to a target. The signal
transmitted by the secondary radar is intercepted and received by the target.
 The target has a transponder on board that interprets the encoded signal and
transmits an encoded reply back to the interrogator. The secondary radar
system receives and interprets the target's encoded signal.
 There are two important parts of Secondary Radar
1.
2.
Ground Interrogator
Air Craft Transponder
Range and Doppler frequency Shift
 Doppler frequency shift:
 Doppler shift is an apparent change in frequency (or wavelength) due
to the relative motion of two objects. Either one or both of the objects
may be moving with respect to the ground.
Range and Doppler frequency Shift
 Doppler frequency shift:
 Thus this change in Frequency tells us that the source is coming
closer or separating.
 Rate of change of frequency could be used to determine the
speed.
 Change in frequency is called Doppler shift in frequency and
change in wavelength is called Doppler shift in wavelength.
 If frequency increases than the transmitted frequency than the
target is approaching and if the frequency decreases than the
transmitted frequency than the target is receding.
Range and Doppler frequency Shift
 Range:
 The actual range of a target from the radar is known as slant range.
 Slant range is the line of sight distance between the radar and the object
illuminated. While ground range is the horizontal distance between the emitter
and its target and its calculation requires knowledge of the target's elevation.
 Since the waves travel to a target and back, the round trip time is dividing by
two in order to obtain the time the wave took to reach the target. Therefore the
following formula arises for the slant range:
R = c0· t/2
c0 = speed of light = 3·108 m/s
t = measured running time [s]
R = slant range antenna - aim [m)
 The distances are expressed in kilometers
or nautical miles (1 NM = 1.852 km).
where:
Radar Applications
Radar Applications
 Space probes can use radar to study the composition of any planets they pass,
as the Cassini probe did when it orbited Saturn.
 Radar can be used to track the movement of aircraft .
Radar Applications
 Meteorologists use weather-sensing radar systems to help locate and forecast
storms.
 Radio telescope arrays are used to study distant celestial objects.
Radar Applications
 Naval vessels use radar to both track enemy and allied craft and navigate
around obstacles.
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Detection and search radar
Missile guidance systems
Radar for biological research
•
Air traffic control and navigation radar
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wikipedia.com
Slideshare.com
radartutorial.eu
fas.org
alphalpha.org
rfcafe.com
authorstream.com
answers.yahoo.com