This document provides a summary of communication, navigation and surveillance (CNS) systems used at Lokpriya Gopinath Bordoloi International Airport in Guwahati, India. It includes acknowledgments and contents sections. The main topics covered are Airports Authority of India (AAI), CNS systems including very high frequency (VHF) modulation and antennas, navigation aids, security equipment, air traffic management including radar, and automation including automatic message switching systems.

1. 1
Lokpriya Gopinath Bordoloi International Airport
Guwahati
SUMMER TRAINING REPORT ON :
COMMUNICATION , NAVIGATION AND SURVEILLANCE
Submitted By:
Rishi Kumar Sinha
Debanuj Sarma
7th
Semester
Department of Electronics And Communication

2. 2
ACKNOWLEDGEMENT
I take this opportunity to express my profound gratitude and deep
regards to Mr. Sarvesh Kumar , Training Coordinator, AAI for
his exemplary guidance, monitoring and constant encouragement
throughout this training.
I would like to give my special thanks to Mr. Ajay Sharma,
Course Coordinator , AAI and my mentors for showing me the
working and purpose of CNS in Airports Authority of India at
Lokpriya Gopinath Bordoloi International Airport, Guwahati ,
despite of their busy schedule.
The industrial exposure we gained through this training program
will be of great benefit in my future career.

3. 3
Contents
Title Page No.
 Airports Authority Of India
A Brief Insight
 Company Profile 5-6
 Functions of AAI 7
 CNS
 Very High Frequency 9-11
 Modulation 11-14
 Antenna 14
 Transmission Lines 15
 NAV-AIDS 16-26
 Security Equipments 26-29
 AIR TRAFFIC MANAGEMENT
 Introduction 31-33
 Radio Detection and Ranging 34-36
 Automatic Dependent Surveillance Broadcast 36-37
 AUTOMATION
 Introduction 37-40
 Automatic message switching system 40-45

4. 4
Airports Authority Of
India
A brief insight

5. 5
Company Profile
The Airports Authority of India (AAI) under the Ministry of Civil
Aviation is responsible for creating, upgrading, maintaining and managing
civil aviation infrastructure in India. It provides Air traffic
management (ATM) services over Indian airspace and adjoining oceanic
areas.
Airports Authority of India (AAI) was constituted by an Act of Parliament
and came into being on 1st April 1995 by merging erstwhile National
Airports Authority and International Airports Authority of India. The
merger brought into existence a single Organization entrusted with the
responsibility of creating, upgrading, maintaining and managing civil
aviation infrastructure both on the ground and air space in the country. It
covers 2.8 million square nautical miles area which includes oceanic area of
1.7 million square nautical miles.
ANS (Air Navigation Services) in Airports Authority of India provides the
Air traffic Services in Indian Airspace and adjacent country airspaces for
both National and International flights.
ANS is further divided into Two Major functional Sections -
 Communication Surveillance and Navigation (CNS)
 Air Traffic Management (ATM)
A T M
 ATM provides all the necessary instructions to the pilot, to follow
and comply for his safe navigation in the Ground as well as in
Airspace.

6. 6
 The primary purpose of ATM/ATC worldwide is to prevent
collisions, organize and expedite the flow of traffic, and provide
information and other support for pilots.
ATC functionality involves mainly three Control Monitoring
Areas/divisions
 Tower (TWR) Control: Terminal services which includes Landing,
Take-OFF, Alerting Fire Services, RWY availability etc, Changing of
Flight levels (height) etc.
 Approach control(APP): Decent of flight, and procedure to be
followed during Landing, Handing over flight to Tower control etc.
 Area Control Centre(ACC): En-route flight Instructions such as
Current directions and future coordinates to the pilot.
C N S
The CNS provides the necessary Infrastructure for ATS operational. CNS is
the backbone for the ATM and to the Aircrafts (pilots) for its operational
providing communication, navigational and surveillance facilities.

7. 7
 COMMUNICATION involves exchange of voice and data
information between ACFT and ATS.
 NAVIGATION enables the pilot in pinpointing the location of the
ACFT.
 SURVEILLANCE assists air traffic controller in pinpointing the
position of the ACFT at any time
Functions Of AAI:
 Design, Development, Operation and Maintenance of
international and domestic airports and civil enclaves.
 Control and Management of the Indian airspace extending
beyond the territorial limits of the country, as accepted by
ICAO.
 Construction, Modification and Management of passenger
terminals.
 Development and Management of cargo terminals at
international and domestic airports.
 Provision of passenger facilities and information system at the
passenger terminals at airports.
 Expansion and strengthening of operation area, viz. Runways,
Aprons, Taxiway etc.
 Provision of visual aids.
 Provision of Communication and Navigation aids, viz. ILS,
DVOR, DME, Radar

8. 8
Communication
Surveillance and
Navigation
(CNS)

9. 9
VERY HIGH FREQUENCY (VHF):
Range: 30Hz to 300MHz
Very high frequency (VHF) is the ITU designation for the range of t from
30 MHz to 300 MHz, with corresponding wavelengths of ten to one meters.
Frequencies immediately below VHF are denoted high frequency (HF), and
the next higher frequencies are known as ultra high frequency (UHF).
Common uses for VHF are radio broadcasting, television broadcasting, two
way land mobile radio systems (emergency, business, private use and
military), long range data communication up to several tens of kilometres
with radio modems, amateur radio, and marine communications. Air traffic
control communications and air navigation system (e.g. VOR, DME & ILS)
work at distances of 100 kilometres or more to aircraft at cruising altitude.

10. 10
It has three modes of propagation:
 Ground Wave Propagation:
Range: up to 2MHz
Ground Wave propagation is a method of radio frequency propagation that uses
the area between the surface of the earth and the ionosphere for transmission.
The ground wave can propagate a considerable distance over the earth's surface
particularly in the low frequency and medium frequency portion of the radio spectrum.
 Sky Wave Propagation
Range: 3MHz to 30MHz
In radio communication, skywave or skip refers to the propagation of
radio waves reflected or refracted back toward Earth from the ionosphere, an
electrically charged layer of the upper atmosphere.
 Space Wave Propagation
Range: above 30MHZ
The radio waves having high frequencies are basically called as spacewaves.
These waves have the ability to propagate through atmosphere, from transmitter

11. 11
antenna to receiver antenna. These waves can travel directly or can travel after
reflecting from earth’s surface to the tropospheresurface of earth. So, it is also called
as Tropospherical Propagation.
MODULATION:
Modulation is a process ofSystematic Alteration of One Waveform, called the Carrier,
according to the characteristic of other waveform which is the Message or information
bearing Waveform.
NEED OF MODULATION:
 Frequency Multiplexing: This is needed for transmission of several
different signals of same spectral length. Such multiple transmissions i.e.
multiplexing may be achieved by translating each one of the original
signal to a different frequency range. If these frequency ranges do not
overlap, then the signal may be separated at the receiving end by
appropriate band pass filter, and the output of the filter processed to
recover the original signal.
 Practicability of Antennas: When free spaceis the communication
channel, antennas radiate and receive the signal. It turns out that antennas
operate effectively only when their dimensions are of the order of
magnitude of the wavelength of the signal being transmitted. A signal of
frequency 1 KHz corresponds to wavelength of 300,000 m, an entirely
impractical length. The required length may be reduced to the point of
practicability by translating the audio tone to a higher frequency.
DIFFERENT TYPES OF MODULATION:
1. Amplitude Modulation:
Modulation in which the amplitude of a carrier wave is varied in
accordancewith some characteristic of the modulating signal.
 Carrier signal equations,

12. 12
C (t) = C sin (ωc + φ)
Where:
carrier frequency in Hertz is equal to ωc / 2 π.
C is the carrier amplitude.
φ is the phase of the signal at the start of the reference
time.
 Modulating signal equations
m (t) = M sin (ωm + φ)
Where:
modulating signal frequency in Hertz is equal to ωm / 2 π.
M is the carrier amplitude.
φ is the phase of the signal at the start of the reference
time.
 Overall modulated signal for a single tone,
y (t) = [ A + M cos (ωm t + φ ] . sin(ωc t)
Or, y (t) = A. sin (ωc t) + M/2 [ sin ((ωc + ωm) t + φ) + M/2 [sin
((ωc - ωm) t - φ)
Where,
Carrier: A . sin (ωc t)
Upper sideband: M/2 [sin ((ωc + ωm) t + φ)]
Lower sideband: M/2 [ sin ((ωc - ωm) t - φ)]
Itcan be seen that for a case where there is 100% modulation, i.e. M = 1, and where
the carrier is not suppressed, i.e. A = 1, then the sidebands havehalf the value of the
carrier, i.e. a quarter of the power each.
Sidebands on an amplitude modulated carrier
when modulated with a single tone

13. 13
2. FREQUENCYMODULATION:
Frequency modulation (FM) is the encoding of information in a carrier
wave by varying the instantaneous frequency of the wave. (Compare
with amplitude modulation, in which the amplitude of the carrier wave
varies, while the frequency remains constant.)
X(t)= A cosθ =A cos (ωt +Ø), θ=cos(ωt+Ø), θ=ωt+Ø
where, A→ Amplitude
θ=ωt +Ø → Angle
Ø → Initial phase
ω →Angular frequency
A is replace by → A + kA cosωmt
→ Amplitude Modulation A(1+ kA cosωmt)cosωct
Ø is replace by→ Ø + kA cosωmt
→ Phase Modulation A cos(ωt+Ø + kA cosωmt)
If by similarity
ω is replaced by (ω + kA cosωmt)
It gives , A cos [(ω+kA cos ωmt )t +Ø]
The angular velocity becomes
d/dt[(ω+kA cos ωmt )t +Ø]
= ω +kA cos ωmt – t kA ωmsin ωmt
1 2 3
Term 3 is ridiculous and impossible to achieve.

14. 14
Therefore Instantaneous angular frequency is the rate of change of angle
and NOT repeats NOT the coefficient of t.
• Therefore the frequency modulation is to be conceived by replacing dθ/dt by ωc
+ K Am cos ωmt
• Spectral analysis gives the FM wave as,
Ac Jo(β) cos ω ct + ΣAC Jn (β)[cos(ωc+nωm) t-cos(ωc-ωm)t]
+ ΣAC Jn (β)[cos(ωc+nωm) t-cos(ωc-ωm)t]
• Note that the odd sideband pairs are in RF quadrature and the even pairs are in
RF phase with the carrier.
Therefore by truncating the second sideband onwards the desired AM will not
be available directly.
ANTENNA:
An antenna (or aerial) is an electrical device which converts electric power into radio
waves, and vice versa. It is usually used with a radio transmitter or radio receiver.
Antennas are essential components of all equipment that uses radio. They are used in
systems such as radio broadcasting, broadcasttelevision, two-way
radio, communications receivers, radar, cell phones, and satellite communications.
Connect receiver and transmitter in free space. Use to transmit electromagnetic waves
in free space.

15. 15
Folded Dipole Antenna:
A Folded dipole is dipole antenna with the ends folded around and connected to each
other forming a loop.
TRANSMISSION LINE:
In communications and electronic engineering, a transmission line is a specialized
cable or other structure designed to carry alternating current of radio frequency, that is,
currents with a frequency high enough that their wave nature must be taken into
account.
Impedance matching:
In electronics, impedance matching is the practice of designing the input impedance of
an electrical load or the output impedance of its corresponding signal source
to maximize the power transfer or minimize signal reflection from the load.
In the case of a complex sourceimpedance ZS and load impedance ZL, maximum
power transfer is obtained when

16. 16
where the asterisk indicates the complex conjugate of the variable.
Where ZS represents the characteristic impedance of a transmission line, minimum
reflection is obtained when
VSWR (Voltage Standing Wave Ratio), is a measure of how efficiently radio-
frequency power is transmitted from a power source, through a transmission line,
into a load (for example, from a power amplifier through a transmission line, to an
antenna).
= reflection coefficient
= ratio of the amplitude of the reflected wave to the incident
wave.
NAV-AIDS:
DISTANCE MEASURING EQUIPMENT :
Range:960MHz to 1215MHz
Distance measuring equipment (DME) is a transponder-based radio navigation
technology that measures slant range distance by timing the propagation
delay of VHF radio signals. DME is similar to secondary radar, except in reverse.
It works on the principle of Radar that is reflection of electromagnetic waves in space.
Aircraft use DME to determine their distance from a land-based transponder by
sending and receiving pulse pairs – two pulses of fixed duration and separation. The
ground stations are typically co-located with VORs.
A low-power DME can be co-located with an ILS glide slope antenna installation
where it provides an accurate distance to touchdownfunction.

17. 17
DME Signal characteristics and Function
Airborne Equipment
The Aircraft Interrogator transmits
an Omni-directional interrogation
The Airborne Interrogator:
• Operates at approximately 25 interrogations per second.
• Uses a pseudo-randomtiming algorithm to recognize the replies to
its own interrogations.
The Ground Transponder:
• Receives interrogations without distinguishing among the
sources.
• Decodes each interrogation to validate it.
• Adds sufficient time so that the complete time from
interrogation to reply is 50µs.
 The DME maintains a minimum duty cycle in order for the aircraft AGC to
work efficiently.

18. 18
 If the total number of interrogations does not generate enough replies to
maintain the minimum transmitter rate, then the transponder generates reply
pairs, called “squitters”, at random times.
 If there are enough replies to produce800 or more reply pulse pairs per second
(pps), then no squitters are produced.

19. 19
DOPPLER VHF OMNI RANGE
Its works on the principle of DopplerEffect.
That is the apparent change in frequency of a wave (or other periodic event) for
an observer moving relative to its source.
DVOR is a navigational aid equipment designed to provide bearing information to
aircraft.VOR Systems composedofa transmitting station on the ground and receiving
station on the aircraft.

20. 20
Here three signals are used:
1.AM SIGNAL(reference signal).its range is 30MHz
2.FM SIGNAL(varying signal)
3.CARRIER SIGNAL
In DVOR 48 antennas are used along with a central antenna. Only 5 antennas can be
used at a time. Central Antenna radiate carrier signal and other antenna radiate
amplitude modulated signal and frequency modulated signal. And in spacethese
signals undergo space modulation. All the information is contained in FM signal and
AM acts as an envelope.
 Counterpoise: use to reflect the information totally.
 By comparing the phase of AM and FM signal will get radial
information.
 ALFORD LOOP ANTENNA is used here.
COMPARING THE TWO 30 Hz SIGNALS AT DIFFERENT
AZIMUTHS

21. 21
EXAMPLE:
VOR SIGNAL FROM PILOT’S POINT OF VIEW (ON SPECTRUM
ANALYZER)
INSTRUMENT LANDING SYSTEM:
An instrument landing system (ILS) is a ground-based instrument approachsystem
that provides precision lateral and vertical guidance to an aircraft approaching and
landing on a runway, using a combination of radio signals and, in many cases, high-
intensity lighting arrays to enable a safe landing during instrument meteorological
conditions (IMC), suchas low ceilings or reduced visibility due to fog, rain, or
blowing snow.

22. 22
It has two parts:
1. LOCALIZER: It gives information about the central line.
The localizer information is typically displayed on a course deviation indicator (CDI)
which is used by the pilot until visual contact is made and the landing completed. The
localizer radiates on a carrier frequency between 108 to 112 MHz with 50 kHz
channel spacing. This carrier is modulated with audio tones of 90 Hz, 150 Hz.
The localizer antenna array radiates two different signals: Carrier sideband (CSB) and
Suppressed carrier sideband only (SBO). The CSB signal consists of the RF carrier
amplitude modulated (AM) with equal amplitudes of 90 Hz and 150 Hz tones. The
SBO signal is similar except that the carrier is suppressed.
If the aircraft on approachis aligned with the runway centreline , the CDI will display
no difference in the depth of modulation (DDM) between the 90 Hz and 150 Hz audio
tones; therefore, the CDI needle is centred.
If the aircraft is to the right of the centreline, the 150 Hz modulation will exceed that
of the 90 Hz and producea deflection on the CDI towards the left. Conversely, if the
aircraft is to the left of the centreline, the 90 Hz modulation will exceed that of the 150
Hz and producea similar but oppositedeflection.
The CDI has a full-scale deflection of 150 microamperes where the DDM equals
0.155 in both the 90 Hz and 150 Hz directions. The angular displacement, or
proportional guidance sector, that correspondsto this full scale deflection is known as

23. 23
the localizer course width. When the aircraft is outside this course guidance sector, the
CDI is required to provide full scale deflection. This region is known as the clearance
sector.
CSB RF RADIATED PATTERN
SBO RF RADIATED PATTERN

24. 24
2.GLIDE PATH:
 Frequency range: 329.15 - 335 MHz(Bhubaneswar-331MHz)
 2.5 - 3 degrees above horizon.
The glide slope provides the pilot with vertical guidance. This signal gives the pilot
information on the horizontal needle of the CDI to allow the aircraft to descend at the
properangle to the runway touchdown point. The glide slope radiates on a carrier
frequency between 329 and 335 MHz and is also modulated with 90 Hz and 150 Hz
tones. The glide slope frequencies are paired with the localizer, meaning the pilot has
to tune only one receiver control. The radiation patterns of a typical glide slope
system are similar to those of the Localizer.

25. 25
The glide path angle is normally referenced at 3 degrees. If the aircraft is on this three-
degree glide path, equal amounts of the 90 Hz and 150 Hz are received and the CDI
will be centred. If the aircraft is above the glide path, the 90 Hz modulation exceeds
that of the 150 Hz and produces a deflection on the CDI downwards. If the aircraft is
below the established glide path, the 150 Hz modulation predominates and produces a
similar but oppositedeflection.
The glide slope sensitivity is set so that the full-scale indications occurat
approximately 2.3 and 3.7 degrees elevation.
NON DIRECTIONAL BEACON:
 A non-directional beacon, also called a low or medium frequency
homing beacon transmits non-directional signals.
 A pilot of an aircraft suitably equipped with a directional antenna and
receiver can determine his bearing to the ground beacon and “home”
on it with the help of these signals.
 These facilities operate on frequencies available in that portion of the
frequency band between 190 and 1750 KHz (however, the frequency
band is selected according to the purpose for which it is designated),
with identification normally provided by keyed 1020 Hz or 400Hz
modulation, continuous carrier.
PURPOSE OF NDB -
 As an enroute Aid:- NDB is most useful as a long range enroute aid,
because it points the direction of the NDB from distances as large as
1000 miles. A series of NDBs located at strategic points help the
aircraft’s movement from one point to another.
 Position Fixing: Aircraft can get its position fixed on a map if it takes
its Relative Bearing from two NDBs.
 As an Aid to Final Approach: Low Power NDBs located along with
Middle and Outer Markers are called Middle Locator and Outer
Locator. This helps the aircraft to reach and adjust proper approach
path in Instrument Landing System (ILS).

26. 26
 Weather Broadcast: The NDB transmitter is capable of transmitting
audio signals on the carrier. Usually identification is transmitted in the
form of coded tone. Voice transmission can also be made. Weather
messages can also be voice modulated and transmitted. This facility is
not used in India.
SECURITY EQUIPMENTS
OBJECTIVESOF SECURITYCHECKS:
 Prevents attack on aircraft and airport.
 Ensure safety and security for passengers.
 Prevent accidents due to hazardous materials.
 X-RAY SCANNING
 Screening of baggage
 To ensure that hazardous materials not taken in aircraft
X-RAY THEORY:
X-Rays as electromagnetic radiation of very short wavelength, which are emitted
when fast moving electrons strike a target of high atomic weight .These are highly
penetrating rays, passed through some of the materials and absorb by some of the
materials depending upon the density and mass of the materials.
X-Rays systems distinguish the materials according to their atomic weight and density
.The are then displayed in colours according to the materials.
 Orange colour-organic materials(e.g.:-cotton, wool, alcohol ,explosives etc)
 Green colour-inorganic materials(e.g.:-salt ,glass ,pvc etc)
 Purple colour- metals(e.g.:-copper ,iron)

27. 27
X-Ray Baggage Inspection System (XBIS) equipped with high resolution Dual Energy
Solid State Detector which produces sharp and clear X-ray real time images for
baggage inspection in security areas.
Three types of X-BIS machines are used in Airport:
 Register baggage
 Hand baggage
 Cargo screening
X-BIS for Hand Baggage X-BIS for RegisterBaggage

28. 28
X-BIS for Cargo Baggage
DOOR FRAME METAL DETECTOR :
Door Frame Metal Detector walk-through metal detector which uses advanced
magnetic technology to accurately pinpoint the location, size, and number of
concealed weapons, such as knives and guns Personal artifacts such as coins, keys
or belt buckles will not set off the alarm. It offers superior performance for
demanding high security applications.
HAND HELD METAL DETECTOR:
A metal detectoris an electronic instrument which detects the presence of metal
nearby. Metal detectors are useful for finding metal inclusions hidden within
objects, or metal objects buried underground. They often consist of a handheld unit
with a sensorprobewhich can be swept over the ground or other objects. If the

29. 29
sensorcomes near a piece of metal this is indicated by a changing tone in
earphones, or a needle moving on an indicator. Usually the device gives some
indication of distance; the closer the metal is, the higher the tone in the earphone or
the higher the needle goes. Another common type are stationary "walk through"
metal detectors used for security screening at access points in prisons, courthouses,
and airports to detect concealed metal weapons on a person's body.
Other Security Equipments include -
 Liquid Explosives Detector
 CCTV
 Walkie Talkie

30. 30
Air Traffic
Management

31. 31
Air Traffic Management is an aviation term encompassing all systems that
assist aircraft to depart from an aerodrome, transit airspace, and land at a destination
aerodrome, including air traffic control (ATC), aeronautical meteorology, air
navigation systems (aids to navigation), Air Space Management (ASM),Air Traffic
Services (ATS), and Air Traffic Flow Management (ATFM), or Air Traffic Flow and
Capacity Management (ATFCM).
 Air Traffic Control - Service provided by ground-based controllers who
direct aircraft on the ground and through controlled airspace, to prevent
collisions, ATC enforces traffic separation rules, which ensure each aircraft
maintains a minimum amount of empty spacearound it at all times. The
objectives of Air traffic control service is preventing collisions between aircraft
and expediting and maintaining in an orderly flow of air traffic.
The areas of responsibility for TWR controllers fall into three general
operational disciplines; Aerodrome Control, Surface Movement Control or
Ground Control, and Clearance Delivery—other categories, such
as Apron Controlor Ground Movement Planner, may exist at extremely busy
airports.

32. 32
 Air Traffic Advisory Service - used in uncontrolled airspace to prevent
collisions by advising pilots of other aircraft or hazards
 The ApproachControl Service is an air traffic control service in the
Terminal Control Area (TMA) and the ControlZone (CTR), which
is provided for controlled flights of aircraft arriving at one or more
airports under the TMA or departing from them.
 The Area ControlCentre (ACC ) provides an air traffic control
service for controlled flights in controlled area (CTA). The air
traffic control service is provided continuously in Indian airspace by
22 ACCs in 5 FIRs.
 Ground Control(sometimes known as Ground Movement Control)
is responsible for the airport "movement" areas, as well as areas not
released to the airlines or other users. This generally includes all
taxiways, inactive runways, holding areas, and some transitional
aprons or intersections where aircraft arrive, having vacated the
runway or departure gate. Exact areas and control responsibilities
are clearly defined in local documents and agreements at each
airport. Any aircraft, vehicle, or personwalking or working in these
areas is required to have clearance from Ground Control. This is
normally done via VHF/UHF radio, but there may be special cases
where other procedures are used. Aircraft or vehicles without radios
must respond to ATC instructions via aviation light signals or else
be led by vehicles with radios. People working on the airport
surface normally have a communications link through which they
can communicate with Ground Control, commonly either by
handheld radio or even cell phone. Ground Controlis vital to the
smooth operation of the airport, becausethis position impacts the

33. 33
sequencing of departure aircraft, affecting the safety and efficiency
of the airport's operation.
 Clearance Delivery is the position that issues route clearances to
aircraft, typically before they commence taxiing. These contain
details of the route that the aircraft is expected to fly after departure.
Clearance Delivery or, at busy airports, the Traffic Management
Coordinator (TMC) will, if necessary, coordinate with the en route
centre and national command centre or flow control to obtain
releases for aircraft. Often, however, such releases are given
automatically or are controlled by local agreements allowing "free-
flow" departures. When weather or extremely high demand for a
certain airport or airspace becomes a factor, there may be ground
"stops" (or"slot delays") or re-routes may be necessary to ensure
the system does not get overloaded. The primary responsibility of
Clearance Delivery is to ensure that the aircraft have the proper
route and slot time.
 Flight Information Service - which provides information useful for the safe
and efficient conductof flights
 Alerting Service - which provides services to all known aircraft, will
accomplish the objectives of notifying appropriate organizations regarding
aircraft in need of search and rescue aid

34. 34
RADIO DETECTION AND RANGING
Radar is an object-detection system that uses radio 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. The object returns a tiny part of the wave's energy to a
dish or antenna that is usually located at the same site as the transmitter.
Principles:
 Radar signal
A radar system has a transmitter that emits radio waves called radarsignals in
predetermined directions. When these come into contactwith 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 ground. Some of these make the use
of radar altimeters possible. The radar signals that are reflected backtowards
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.
Radar receivers are usually, but not always, in the same location as the
transmitter. Although the reflected radar signals captured by the receiving
antenna are usually very weak, they can be strengthened by electronic
amplifiers. More sophisticated methods of signal processingare also used in
order to recover useful radar signals.
 Illumination
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 ofdirecting artificial radio
waves towards objects is called illumination, although radio waves are invisible
to the human eye or optical cameras.
 Reflection
Radar waves scatter in a variety of ways depending on the size (wavelength) of
the radio wave and the shape of the target. If the wavelength is much shorter
than the target's size, the wave will bounceoff in a way similar to the way light

35. 35
is reflected by a mirror. If the wavelength is much longer than the size of the
target, the target may not be visible becauseof poorreflection. Low-frequency
radar technology is dependent on resonances for detection, but not
identification, of targets. This is described by Rayleigh scattering, an effect that
creates Earth's blue sky and red sunsets. When the two length scales are
comparable, there may be resonances. Early radars used very long wavelengths
that were larger than the targets and thus received a vague signal, where as
some modern systems use shorter wavelengths.
 Doppler Effect
Frequency shift is caused by motion that changes the number of wavelengths
between the reflector and the radar. That can degrade or enhance radar
performance depending upon how that affects the detection process.
Doppler shift depends upon whether the radar configuration is active or passive.
Active radar transmits a signal that is reflected back to the receiver. Passive
radar depends upon the object sending a signal to the receiver.
Types-
 Primary radar
The rapid wartime development of radar had obvious applications for air traffic
control (ATC) as a means of providing continuous surveillance of air traffic
disposition. Precise knowledge of the positions of aircraft would permit a
reduction in the normal procedural separation standards, which in turn promised
considerable increases in the efficiency of the airways system. This type of
radar (now called a primary radar) can detect and report the position of
anything that reflects its transmitted radio signals including, depending on its
design, aircraft, birds, weather and land features. Forair traffic control purposes
this is both an advantage and a disadvantage. Its targets do not have to co-
operate, they only have to be within its coverage and be able to reflect radio
waves, but it only indicates the position of the targets, it does not identify them.
When primary radar was the only type of radar available, the correlation of
individual radar returns with specific aircraft typically was achieved by the
controller observing a directed turn by the aircraft.
 Secondary radar
The need to be able to identify aircraft more easily and reliably led to another
wartime radar development, the Identification Friend or Foe (IFF) system,
which had been created as a means of positively identifying friendly aircraft
from enemy. This system, which became known in civil use as secondary
surveillance radar (SSR), or in the USA as the air traffic control radar beacon
system (ATCRBS), relies on a piece of equipment aboard the aircraft known as
a "transponder." The transponder is a radio receiver and transmitter pair which

36. 36
receives on 1030 MHz and transmits on 1090 MHz The target aircraft
transponder replies to signals from an interrogator (usually, but not necessarily,
a ground station co-located with a primary radar) by transmitting a coded reply
signal containing the requested information

37. 37
Automatic Dependent Surveillance Broadcast
It is costefficient alternative for secondarysurveillance radar (SSR)and
provides high performance. It is compact, requires minimum power, has no RF
emissions and can be easily installed
FunctionsOf Main Components-
 Quadrant Sensor receive the incoming RF signal. Convert analog to digital and
then digital signal processing is done and final output is given to QCMS
application.
 The Quadrant Low Power Site Monitor is reference transponder, periodically
transmits ADS-B messages. It is used to verify the properfunctioning of
Quadrant Sensor.

38. 38
 Quadrant Interrogator Controller (QIC) schedules all transmission & make sure
that consecutive interrogations are separated by a certain amount of Time.
 Enhanced Supervision Management System (ESMS) is control and Monitoring
System to ensure a continued high integrity of Provided services. This uses
SNMP to get reports from the component about health and status.
 LAN Switches are used to interconnect different components of ADS-B
System.
 Dual UPS system is used to provide redundant uninterrupted power supply to
different component of ADS-B system.

39. 39
Automation

40. 40
Automationis the use of control systems and information
technologies to reduce the need for human work in the production of
services.
Automation in ATS enhances:
 Safety
 Efficiency (which may include flexibility, potential cost savings, and
reduction in staffing)
 Capacity
 Support to the controller
NEED OF ATS AUTOMATION -
 The user of ATS automation is Air Traffic Management (ATM).
 The job of ATM is to enhance safety, reduce delays and increase
airspace & airport capacity.
 It requires lot of information to be processed efficiently .
 The information is increasing with the air traffic growth.
 Difficult to process so much information manually
ADVANTAGES -
• Tower , Approach & Area ATS functions are integrated and
Automated.
• Multi-Sensor Surveillance Data Tracking and fusion.
• Safety Nets (STCA, APW, MSAW).
• 4-D Trajectory Prediction.

41. 41
• Medium Term Conflict Detection (MTCD).
• RVSM Operation.
• AIDC/ICAO Coordination.
• Synchronized data and voice replaying
• System Availability & Recovery.
• Surveillance Bypass Facility.
AIRCON 2100 ATS AUTOMATION SYSTEM
The Automation System Comprises of the following functional
subsystems:
 Local Area Network (LAN) components
 Common Time System (CTS)
 Radar Data Communication Unit-RX (RDCU)

42. 42
 Flight Data Processor (FDP)
 Surveillance/Situation Data Processor (SDP)
 Safety Net (SNET)
 Data Recording Facility (DRF)
 Control and Monitoring Display (CMD)
 Neptuno Voice Recorder (NEP-VR)
 Neptuno Supervisor position
 Database Management System/Data Management
System(DBM/DMS)
 Situation Data Display (SDD)
 Flight Data Display (FDD)
 Flight Strip printer
 Radar Data Communication Unit-TX (RDCU)
 UPS System

43. 43
AUTOMATIC MESSAGE SWITCHING SYSTEM
 Communication system that provides Air Traffic Service (ATS) messages to
control the air space and movement of Air traffic in an orderly way.
 Designed by ECIL, India.
 Computer-based message switching system.
 Works on Store and forward principle.
 Accepts AFTN (AERONAUTICAL FIXED TELECOMMUNICATION
NETWORK ) message format.
 Works on both Domain based & Non‐domain based network.
 Dual Architecture system
Three major categories of AFTN switching system -
 LINE SWITCHING
It is switching system used for switching lines or circuits. User on demand
basis end-to-end connection like Telephone exchange
 MESSAGE SWITCHING
It is switching system works on store and forward principle in the order of
priority. Provides good line utilization, multi-addressing, message and system
accounting.
 PACKET SWITCHING
This system divides a message into small chunks called packet made of a bit
stream, each containing communication control bits and data bits. It can handle
high-density traffic. Messages are protected until delivered.

44. 44
MAJOR COMPONENTS -
 Core System
E.g.: AMSS Main Servers operated in Hot/Standby combination,
Communication adapters, Multiplexer and Communication server.
 Recording System
E.g.: Mass Data storage devices for incoming /outgoing AFTN messages and
Database Servers.
 Users’ Terminals
E.g.: Workstations.
WORKING OF AMSS -
 AMSS is AFTN Switching System based on computer networking.
 It receives the messages from LAN and remote lines via CCM.
 It analyses the received messages for the correctness ofthe format and address,
stores them in the shared memory and also on online mass- storage media and
automatically retransmits the messages to the addressees according to the
database files at UNIX server.
 In case the message is not as per the format or has incorrect addresses, the
message is rejected and the service message is generated and sent

45. 45
back to the originator of the message.
 While re-transmitting, AMSS keeps in view the precedenceof message.
In the process ofre-transmitting, AMSS checks continuously for the
availability of the line for the destination of message.
 Forsupervision of the switch AMSS sends reports to the supervisory
terminals about changes in status of the system and lines. AMSS
generates periodical statistical and status reports for the supervisor.
 AMSS provides facilities to store the every day’s messages on
the removable media for the long-term storage and retrieval.