PRINCIPLES OF RADAR
Some radar sets are quite weak and emit less power than is used in an ordinary light bulb. Others are so powerful that for very short periods of time the power transmitted could light up an entire town. But in principle they are much the same. They all contain a transmitter, a receiver, an antenna, and an indicator. We shall return to a description of these components, but before doing that, let us see how radar measures the distance to any object, for example, an airplane.
The radar set sends out a pulse of energy in the direction of the airplane (Fig. 1). A small fraction of the energy is reflected back and is detected by the radar. If one knows the speed at which the pulse travels and the time elapsed between transmission and reception of the pulse, one can easily calculate the distance to the airplane. In all radar sets the pulse of energy is in the form of electromagnetic waves, which for most practical purposes can be considered to move at a constant velocity equal to 186,000 miles/sec (5 × 108 meters/sec). Some readers will immediately recognize that this is the velocity of light.