Military radar has remained largely unchanged since its development over 100 years ago.
Working as an active-duty airman in the U.S. Air Force, my primary responsibility was the repair and maintenance of the complex radar system onboard the E-3 Sentry AWACS aircraft. The radar lessons I learned in tech school, however, were exceedingly simple: a transmitter emits a radio wave that is reflected back when it comes in contact with an object.
If that object is moving toward or away from the transmitter, the return signal has a slightly different frequency, caused by the Doppler effect. By calculating the time of flight of a radio wave moving at the speed of light and the Doppler effect, you can determine the distance and speed of most conventional aircraft.
Named after the Austrian physicist Christian Doppler, the Doppler effect is the change in frequency or wavelength of a wave in relation to an observer. It’s the reason why a passing ambulance has that familiar change in pitch as it passes by. Compressed sound waves as it moves toward you are higher pitched, whereas stretched out sound waves as it moves away result in a lower pitch.