Q.What is the principle of RADAR ? Write the applications of RADAR.

RADAR uses the reflection (echo) of transmitted microwave pulses off a target to detect its presence, distance and sometimes velocity; it is widely used in navigation, defence, and meteorology.

Principle

A RADAR transmitter sends out short, powerful pulses of ultra-high-frequency electromagnetic waves (microwaves, typically a few GHz) through a directional antenna. When these waves strike a distant object (aircraft, ship, storm cloud, etc.), part of the energy is reflected back as an echo. The same (or a nearby) antenna receives this reflected pulse. Since electromagnetic waves travel at the speed of light $c$, and the time interval $t$ between transmission of the pulse and reception of its echo is measured electronically, the distance of the object is

$d = \dfrac{c\,t}{2}$

the factor of $2$ accounting for the wave travelling to the object and back. The direction of the antenna when the echo is strongest gives the bearing of the object, and if the object is moving, the Doppler shift of the reflected frequency gives its radial velocity.

Why microwaves are used

Microwaves are used because they travel in straight lines (good directionality with a small antenna/dish), are not absorbed much by the atmosphere, and are reflected efficiently by metallic and other objects.

Applications of RADAR

1. Detecting and tracking the position, direction and speed of aircraft and ships (navigation and collision avoidance). …