MUET, SZAB Khairpur Campus

Subject: Communication System

Teacher: Engr: Toqueer Jumani

Department Of Electrical Engineering 12t

h

Batch

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 (acronym for RAdio Detection And Ranging) is an object-detection 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.

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

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

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

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. Ground Interrogator2. Air Craft Transponder

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 where: 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).

Range and Doppler frequency Shift

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.

• Detection and search radar• Missile guidance systems• Radar for biological research• Air traffic control and navigation radar

1. wikipedia.com

2. Slideshare.com

3. radartutorial.eu

4. fas.org

5. alphalpha.org

6. rfcafe.com

7. authorstream.com

8. answers.yahoo.com