Navigation and Seamanship

6.2.2. Working Principle of Radar

          

          Basically radar works on the same principle as an echo sounder but use radio waves instead of sound waves. Radar sends radio waves with the help of directional antenna to particular direction. The radio wave travels with the speed of light that is 3x10⁸ m/s, hit an object if any, on the way of radio wave and bounce back as echo. Since the waves travel at a constant speed (3x10⁸ m/s), the distance of an object can be calculated by noting the time interval between transmission of a wave and reception of an echo.

           If the travel time of radio wave from antenna to object and back to the antenna as echo is ‘ t’,then the distance(Range-R) between the antenna fitted vessel and the target object may be determined by the simple formula:

R = c t/2
where c = 3 x 10⁸ m/s, the speed of light or radio wave.
The value needs to be taken as 50% because the radio wave pulse travels twice the time of actual required.

Radar signals can be displayed on the Plan Position Indicator (PPI) with rotating vector indicates the pointing direction of the antenna and hence the bearing of targets.