Radar (Radio Detection and Ranging)

Remote detection system used to locate and identify objects. Radar relies on sending and receiving electromagnetic radiation, usually in the form of radio waves or microwaves. Electromagnetic energy moves in waves at or near the speed of light. The wavelength of an electromagnetic wave determines some of the characteristics of the wave. Gamma rays and X-rays have very short wavelengths and can penetrate solid objects. Longer wavelengths such as radio waves or microwaves tend to be reflected by solid objects and are more effective for radar.

Radar creates an electromagnetic energy pulse that is focused by an antenna and transmitted through the air. This focused wave is called the signal. Objects in the path of the signal, called targets, scatter the electromagnetic energy. Some of this scattered energy is reflected or bounces back toward the radar. This is called an echo. The receiving antenna (which is usually the transmitting antenna as well) gathers this radiation and feeds it to a device called a receiver. The receiver reports the return and, depending on the sophistication of the device, simply reports the detection or analyzes the signal for more detailed information.

Radar can determine a number of properties of an object, including its distance, speed, direction of motion, and shape. Radar can detect objects in the dark, beyond a line of sight, and in diverse weather conditions. Even though radio waves and microwaves reflect better than other electromagnetic waves with shorter lengths, only a minute fraction of the radar signal is reflected back (about a billionth of a billionth). This low return requires the radar system to transmit high amounts of energy in the signal.

Radar has many applications, from meteorology to speed limit enforcement. Air defense and tactical military operations are dependent upon airborne and ground-based radar installations to track threats and coordinate attacks. Radar is integral to air and sea navigation, defense, improving traffic safety, and providing scientific data. Air traffic control is highly dependent on large networks of ground-based radar systems.

Meteorologists use radar to observe and forecast the weather. Recent improvements, such as Doppler radar, have been effective for providing tornado, hurricane, and other types of severe weather warnings. Radar is also employed in climate research, for mapping the surface of the earth from orbit, in remote sensing applications, and for investigating the surface of other planets and asteroids.

Radar systems perform the same basic tasks, but the manner in which these are operationalized affects the systems' parts. Pulse radar, for example, sends out bursts of electromagnetic waves at intervals. This requires a method of timing that bursts from the transmitter, causing this type of radar to require a more complex transmitter. Continuous wave radar sends out a continuous signal to obtain detailed information about the target—about its speed and direction, for example. Because this type of radar is more dependent on the return, or echo, it requires a more complex receiver.