Radio waves are that part of the
electromagnetic spectrum with wavelengths longer than
infrared light. Naturally-occuring radio waves are produced by
lightning, or by
astronomical objects. Artificially-generated radio waves are used for
broadcasting, mobile and fixed communications, navigation, computer networks and innumerable other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves may cover a part of the Earth very consistently, shorter waves can reflect off the
ionosphere and travel around the world, and much shorter wavelengths bend or reflect very little and travel on a line of sight.
Diagram of the electric (E) and magnetic (H) fields of Radio Waves emanating from a radio transmitting
antenna (small dark vertical line in the center). The E and H fields are perpendicular as implied by the phase diagram in the lower right.
Discovery and utilization
Radio waves were first predicted by mathematical work done in 1865 by
James Clerk Maxwell. Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. He then proposed
equations, that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887,
Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical the use of radio waves to transfer information through space.
Nikola Tesla and
Guglielmo Marconi are credited with inventing systems to allow radio waves to be used for communication.
Radio portion of the electromagnetic spectrum
Radio waves are divided up into bands by frequency (and corresponding
wavelength) as shown in the radio
frequency spectrum table below.
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