What is RADAR ?????

"RADAR" is Radio Detetion And Ranging which is a communication medium to detect the objects which are at a distance that cannot be obsrved visually.It is one of the applications of microwave.
Principle:

Radar is based on the principle that the R.F signal at a high frequency is reflected back by the conducting target
To determine the distance:

The distance between the target and RADAR unit is measured in 'nautical miles'(nmi). The RADAR unit is essentially an antenna which transmitts and receives R.F signals.The target may be an airplane ,missile or ship.

1 nautical mile=6076 feet

The transmitted R.F signal is reflected by the target and send back to the antenna. The reflected signal is known as 'echo'.The time taken by the signal to travel one nmi is 6.18micro seconds.since the signal is transmitted and received it travells at a speed of 12.34 (6.18x2) micro seconds per nautical mile.The formula to determine the distance of the object 'S' is

S=T/12.34

where 'T' is the time taken for the transmission and reception of the signal.