The basic principle behind radar technology is relatively simple — radar transmits a stream or “beam” of energy in discrete pulses that propagate away from the radar antenna at approximately the speed of light.
The volume of each pulse of energy determines how many targets are illuminated. This directly determines how much energy (power) is returned to the radar. The shape of the radar antenna, the wavelength, of the energy transmitted, and the length of time the radar transmits determine the shape and volume of each radar pulse.
Regardless of where its mounted (plane, ship or ground), a radar system needs the same basic set of components: something to generate radio waves, something to send them out into space, something to receive them, and some means of displaying information so the radar operator can quickly understand it.
The radio waves used by radar are produced by a piece of equipment called a magnetron. Radio waves are similar to light waves: they travel at the same speed but their waves are much longer and have much lower frequencies.
Light waves have wavelengths of about 500 nanometers (500 billionths of a meter, which is about 100–200 times thinner than a human hair), whereas the radio waves used by radar typically range from about a few centimeters to a meter — the length of a finger to the length of your arm — or roughly a million times longer than light waves.
Both light and radio waves are part of the electromagnetic spectrum, which means they’re made up of fluctuating patterns of electrical and magnetic energy zapping through the air.
The waves a magnetron produces are actually microwaves, similar to the ones generated by a microwave oven. The difference is that the magnetron in a radar has to send the waves many miles, instead of just a few inches, so it is much larger and more powerful.
Radar Antennas
Once the radio waves have been generated, an antenna, working as a transmitter, hurls them into the air in front of it. The antenna is usually curved so it focuses the waves into a precise, narrow beam, but radar antennas also typically rotate so they can detect movements over a large area.
The radio waves travel outward from the antenna and keep going until they hit something. Then some of them bounce back toward the antenna in a beam of reflected radio waves.
The speed of the waves is critical for military operations. With an enemy jet approaching at over 2,000 mph, the radar beam needs to travel much faster than this to reach the plane, return to the transmitter, and trigger the alarm in time. If an enemy plane is 100 miles away, a radar beam can travel that distance and back in less than a thousandth of a second.
The antenna doubles up as a radar receiver as well as a transmitter. In fact, it alternates between the two jobs. Typically it transmits radio waves for a few thousandths of a second, then it listens for the reflections for anything up to several seconds before transmitting again.
Another key component of a radar system is the duplexer. This makes the antenna swap back and forth between being a transmitter and a receiver. While the antenna is transmitting, it cannot receive — and vice versa.
Want to learn more? Tonex offers Radar Communications Training, a 2-day course that covers in-depth aspects of radar communications systems including engineering and operations.
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