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
Air Craft Surveillance
Bikas Chandra Sadashiv
ECE – I
• RADAR Frequencies
• RADAR Applications
• Types of RADAR
Topics To Be Covered
• RADAR is stand for Radio Detection And
Ranging and was developed prior to World
• Today RADAR is extremely important in civil
• 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 GHz).
• RADAR systems are in SHF bands because:
a) These frequencies are free from disturbance.
b) Higher frequency, shorter wavelength,
RADAR more effective.(shorter wavelengths
are reflected more efficiently.)
RADAR has a wide range applications including
1. Ground RADAR : extensively used by Air
Traffic Control to separate aircrafts.
2. Airborne Weather RADAR: used by pilots. It
provide pilots with information regarding
(PSR & SSR)
Classifications of RADAR
1) En-Route Surveillance Radar (RSR)
• En-Route Surveillance Radars (RSR) are long
range radars which the signal goes to 300 NM.
• It operates with frequency between 1 to 2
• It used for airway surveillance to provide
range and bearing of aircraft.
**Surveillance: close observation, especially of
a suspected spy or criminal.
2) Terminal Approach Radar (TAR)
• 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 radar
• Thus, the ATC could know the position of
aircraft. through the RADAR display.
Primary Surveillance Radar (PSR)
Secondary Surveillance Radar (SSR)
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 equipment.
• 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 transponder.
How SSR Works?
• The ground secondary radar transmits 1030MHz signal.
• The aircraft radar receives on 1030MHz and transmits back
• The transponder reply is more powerful than the reflected
radar signal allowing for far greater range. (250nm).
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 18-40Ghz)
• 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 in order.