Radar PSR, SSR, COM and Weather Rardar


Radar ( RAdio Detection And Ranging) is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft,guided missilesmotor vehiclesweather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter. Radar is used on airport as aircraft anticollision systems and flight control system.
There are three type of radar used for flight control:

  • PSR (Primary Surveillance Radar)
  • SSR (Secondary Surveillance Radar)
  • COM (PSR and SSR)


Primary Radar

Electromagnetic waves reflect (scatter) from any large change in the dielectric constant ordiamagnetic constants. This means that a solid object in air or a vacuum, or other significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves.
PSR recieve the following data:
  • Aircraft range
  • Aircraft Azimuth
The average coverage of PSR is 100 nautical miles .




Secondary Radar


Secondary surveillance radar (SSR) is a radar system used in air traffic control (ATC), that not only detects and measures the position of aircraft i.e. range and bearing, but also requests additional information from the aircraft itself such as its identity and altitude. Unlike primary radar systems that measure only the range and bearing of targets by detecting reflected radio signals, SSR relies on targets equipped with a radar transponder, that replies to each interrogation signal by transmitting a response containing encoded data. SSR is based on the military identification friend or foe (IFF) technology.

The average coverage of PSR is 220 nautical miles .



Radar COM

This include Radar PSR and SRS.






Weather Radar

Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rainsnowhail, etc.). Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.
Weather radars send directional pulses of microwave radiation, on the order of a microsecond long, using a cavity magnetron or klystron tube connected by a waveguide to a parabolic antenna. The wavelengths of 1 to 10 cm (4 in) are approximately ten times the diameter of the droplets or ice particles of interest, because Rayleigh scattering occurs at these frequencies.
Between each pulse, the radar station serves as a receiver and listens for return signals from particles in the air. The duration of the "listen" cycle is on the order of a millisecond, which is a thousand times longer than the pulse duration. The length of this phase is determined by the need for the microwave radiation (which travels at the speed of light) to propagate from the detector, to the weather target, and back again, a distance which could be several hundred kilometers. The horizontal distance from station to target is calculated simply from the amount of time that lapses from the initiation of the pulse to the detection of the return signal. (The time is converted into distance by multiplying by the speed of light in air) :
Distance = c\ \frac {\Delta t}{2n} (c = speed of light = 299,792.458 km/s, n = refractive index of air ~= 1.0003).



The most frequent use of the radar is located at airports to supportthe air traffic control and safety as well as in meteorological research for studying  violent weather phenomena, or in territorial management in the prevention of extreme weather events such as floods, or to monitor the trend of events such as tornadoes or hurricanes.


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