Radar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft &ships.Radar uses include:Air traffic control:Precision approach and landing guidance to aircraft.Weather Forecasting / Severe weather detectionMeasuring ocean surface wavesPolice detection of speeding trafficSatellite
Super High FrequencySHF3 GHz - 30 GHz0.10m - 0.01m
The need to be able to identify aircraft more easily and reliably led to another radar development SSR-Secondary Surveillance was developed in the late 1960s. It was another form of radar surveillance that receives transmission reflections every few seconds. However, these reflections provide much more data than in primary surveillance. These reflections are digitized messages that report each aircraft's identifications and altitude.These information are transmitted back by the Aircraft’s Transponder on the 1030 MHz back to the ground SSR’s Antennae
Radar operates on the 3,000 to 10,000 MHz frequency bands. (super high frequency SHF)Electromagnetic energy radiating outward from a source is reflected back by objects in its path.The time difference between transmission (trace) and reflection (echo) is measured giving an accurate indication of an objects distance.Distance, azimuth, and elevation can be used to fix the objects position in three dimensional space.Signal timing is critical to accuracy. (one microsecond error results in a distance error of almost 500ft.)As a result position accuracy is directly related to the accuracy of the timing device used.An enormous amount of energy must be transmitted in order for even a small amount to be reflected back.Radar must be very powerful as a transmitter and very sensitive as a receiver.This powerful transmitter would completely overpower the receiver. The problem is corrected by alternating the transmit and receive functions at very brief intervals (signal sharing) and at very high rates. (at a range of 40nm radar cycles between transmitting and receiving approx. 800 times/sec.) SHF waves are subject to line-of-sight limitations, which limit range and create problems with terrain masking.Radar has difficulty differentiating between different types of objects.It will show returns from aircraft, terrain, precipitation, flocks of birds, built up areas such as cities.-Primary Surveillance is a form of radar surveillance developed after World War II. It relies on the "skin effect," which is the reflection of the transmitted radar signal from the aircraft's metallic skins. Thus, air traffic controllers were able to observe the horizontal position of the aircraft.Determines the position of contacts by measuring and displaying reflected radio frequency signals from the contacts.The information is displayed to the user on an oscilloscope. (scope)Detects and reports reflections of aircraft, weather, flocks of birds, built-up areas, and terrain.It is a short range radar effective to 80nm.There is no way to tell one aircraft from another without having the pilots verify position.
The SSR interrogates aircraft by means of pulse trains forming questions (interrogation mode). Aircraft transponder interpret these questions and transmit back the pulse train which are replies that contain information relate to questions (interrogation). SSR receivers capture these signals and transform them for analysis and processing. SSR is complement to the primary radar as it provide ATC with additional info about aircraft such as aircraft’s call sign, altitude, speed and destination.SSR requires an aircraft to be fitted with transmitter/receiver called as transponder.Secondary Radar The principles of operation of primary radar and some of the factorswhich affect a radar’s performance have been illustrated. Some of the effects can beminimised by using Secondary Radar techniques. The principle of measuring range from atime delay is still applicable, but the target plays an active role.The interrogating radar unit sends out a pulse (interrogation pulse). When this pulse isdetected at the target, it triggers a transmitter to respond, sending a signal back to theinterrogator. This signal will be stronger than an echo, will not be dependent on how well thetarget has reflected the energy and could be coded with additional information.
-Secondary Surveillance was developed in the late 1960s. It was another form of radar surveillance that receives transmission reflections every few seconds. However, these reflections provide much more data than in primary surveillance. The transponder is a radio receiver and transmitter which receives on one frequency (1030 MHz) and transmits on another (1090 MHz).
Air craft surveillance & instrumental landing system
Air Craft Surveillance
Bikas Chandra Sadashiv
ECE – I
Types of RADAR
Topics To Be Covered
RADAR is stand for Radio Detection
And Ranging and was developed prior
to World War II.
Today RADAR is extremely important
in civil aviation.
It is used by ATC to monitor and
control numbers of aircrafts in
airspace as well as by pilot for
weather warning and navigation.
Radar operates on UHF and SHF -
Super High Frequency (1 GHz - 30
RADAR systems are in SHF bands
a) These frequencies are free from
b) Higher frequency, shorter
wavelength, RADAR more
effective.(shorter wavelengths are
reflected more efficiently.)
RADAR has a wide range applications
1. Ground RADAR : extensively used by
Air Traffic Control to separate
2. Airborne Weather RADAR: used by
pilots. It provide pilots with
information regarding weather ahead.
Radar (PSR &
1) En-Route Surveillance Radar
En-Route Surveillance Radars (RSR)
are long range radars which the signal
goes to 300 NM.
It operates with frequency between 1
to 2 GHZ.
It used for airway surveillance to
provide range and bearing of aircraft.
**Surveillance: close observation,
especially of a suspected spy or
2) Terminal Approach Radar
TAR is a high definition radio detection
device which provides information on
identification, air speed, direction and
altitude of aircraft to assist air traffic
controllers to track the position of aircraft
in the air within the vicinity of the airport.
This radar gives the air traffic controller a
better or true picture of all aircraft flying
in his control zone.
Working of PSR :
Primary Surveillance Radar (PSR)
transmits a high power signal.
When a signal strikes an object or target,
some signal energy is reflected back and is
received by the radar receiver.
RADAR receiver will plot the direction and
the distance of the target (aircraft) from the
Thus, the ATC could know the position of
aircraft. through the RADAR display.
Primary Surveillance Radar
Secondary Surveillance Radar
Working of SSR :
Secondary Surveillance Radar (SSR)
transmits an interrogation signal which is
received by the target aircraft.
The aircraft transponder sends back a
coded reply to the ground radar
From the coded signal, information of the
aircraft’s call sign, altitude, speed and
SSR requires an aircraft to be fitted with
transmitter/receiver called as
How SSR Works?
The ground secondary radar transmits 1030MHz
The aircraft radar receives on 1030MHz and transmits
back 0n 1090MHz.
The transponder reply is more powerful than the
3) Surface Movement Radar (SMR)
SMR installed at airport (at top of ATC
tower building) to provide a very accurate
radar display in all weathers and conditions
of visibility. (operate with frequency 18-
SMR radar display can show all of airfield
infrastructure including aircraft movements
on runway, taxiway and apron.
It is designed to provide clear display of all
aircraft on runway or taxiway so that ATC
can ensure runway are clear for take-
off/landing and also guide aircraft to apron
The Uses of ILS
How Localizer Works
How Glide Path Works
Topics To Be
Radio beam transmitter that
provides a direction for
approaching aircraft that
tune their receiver to the
The Uses of ILS
To guide the pilot during the
approach and landing.
◦ Very helpful when visibility is
To provide an aircraft with a
precision final approach.
To provide an aircraft guidance to
the runway both in the horizontal
and vertical planes.
ILS consists of Ground Installations and Airborne
There are 3 equipments for Ground Installations, which
1. Ground Localizer (LLZ) Antenna – To provide
2. Ground Glide path (GP) Antenna – To provide
3. Marker Beacons – To enable the pilot cross check
the aircraft’s height.
There are 2 equipments for Airborne Equipments, which
1. LLZ and GP antennas located on the aircraft
2. ILS indicator inside the cockpit
Localizer is the horizontal antenna array located at the opposite
end of the runway.
Localizer operates in VHF band between 108 to 111.975 MHz
Transmit two signals which overlap at the
The left side has a 90 Hz & right has a 150 Hz
The overlap area provides the on-track signal.
How Localizer Works
Needle indicates direction
Centered Needle = Correct
Glide Path Antenna Array
Glide Path is the vertical antenna located
on one side of the runway about 300 m to
the end of runway.
Glide Path operates in UHF band between
329.15 and 335 MHz
How Glide Path Works
Glide path produces two signals in the vertical
The upper has a 90 Hz modulation and the bottom
has a 150 Hz modulation.
Marker beacons operating at a carrier
frequency of 75 MHz are provided.
When the transmission from a marker
beacon is received it activates an
indicator on the pilot's instrument
The correct height the aircraft should
be at when the signal is received in an
Non-Instrument Runway (NI)
Non-Precision Runway (NP)
Precision Runway (P)
Types of Runway Approach
1.Non-Instrument Runway (NI)
◦ A runway intended for the operation of aircraft
using visual approach procedure
2. Instrument Runway
◦ A runway intended for the operation of aircraft
using instrument approach procedures
a) Non-Precision Runway (NP)
• An instrument runway served by visual aids and
a non-visual aid providing at least lateral
guidance adequate for a straight-in approach
b) Precision Runway (P)
• Allow operations with a decision height and
How ILS works?
Ground localizer antenna transmit VHF signal in
direction opposite of runway to horizontally guide aircraft
to the runway centre line.
Ground Glide Path antenna transmit UHF signal in
vertical direction to vertically guide aircraft to the
Localizer and Glide Path antenna located at aircraft
nose receives both signals and sends it to ILS
indicator in the cockpit.
These signals activate the vertical and horizontal
needles inside the ILS indicator to tell the pilot either
go left/right or go up/down.
By keeping both needles centered, the pilot can guide
his aircraft down to end of landing runway aligned with
the runway center line and aiming the touch down.