RADAR

RADAR

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 missiles, motor vehicles, weather 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 basic principles 

The following figure shows the operating principle of a primary radar set. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

 RADAR TYPES:

·       Primary Surveillance Radar (PSR)
·       Secondary Surveillance Radar (SSR)

Primary Radar:
 

Primary radar systems receive reflections of their own transmitted signals as returned signals from the target. The reflected energy is used by the primary radar to determine the target information. Conventionally, the term primary is dropped when referring to primary radar systems as this is considered the normal method of radar operation. The exception to this convention comes when making a distinction between primary radar systems and secondary radar systems. There are three major types of primary radar; mono-static, bi-static and multi-static radar. 

Secondary radar:

Secondary radar uses transponder information to display details about a plane like its identity and altitude, so is the most important. In the absence of a transponder signal, controllers must pick out an unidentified blip on the screen from all the other aircraft they're dealing with, not such an easy task. And it's further complicated because some areas don't have primary radar, meaning a plane passing through them with no transponder signal simply disappear. 

  

Difference between Primary and Secondary Radar: 

Primary Radar provides 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.

Primary radar can detect and report the position of anything that reflects its transmitted radio signals. While secondary radar is with (IFF) system, relies on "transponder." The transponder is a radio receiver and transmitter which receives on one frequency (1030 MHz) and transmits on another (1090 MHz). The target air craft’s 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.