RF communication, electro magnetic waves

An electromagnetic wave is a disturbance made up of coupled electric and magnetic fields that travel together through space. The two fields lie at right angles to each other and to the direction of travel, and they sustain one another as the wave moves, so no medium is needed and electromagnetic waves can pass through a vacuum. In free space they all travel at the speed of light. Radio communication uses the lower-frequency part of this family of waves, generated by causing electric charge to oscillate in an antenna.

The frequency and wavelength of an electromagnetic wave are linked: their product equals the speed of light, so a higher frequency means a shorter wavelength. The full electromagnetic spectrum spans from very low radio frequencies through microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays, each region differing only in frequency and wavelength. The radio portion is itself divided into bands, and the choice of band shapes how a signal behaves.

How radio waves spread, or propagate, depends strongly on their frequency. Lower-frequency waves can follow the curve of the ground or bounce off the ionosphere to travel beyond the horizon, while higher-frequency waves tend to travel in straight lines and are limited to roughly line-of-sight paths, though they can carry more information. Along the way waves are weakened by distance and absorption and can be reflected, refracted and diffracted by terrain and the atmosphere. Understanding these effects lets engineers select frequencies and antenna heights to give reliable coverage for broadcasting and communication.

Frequently asked questions

What is an electromagnetic wave?: It is a self-sustaining disturbance of coupled electric and magnetic fields that travel together at the speed of light and need no medium, so they can cross a vacuum.
How are frequency and wavelength related?: They are inversely related: their product equals the speed of light, so a higher frequency corresponds to a shorter wavelength.
Why does propagation depend on frequency?: Lower frequencies can follow the ground or reflect off the ionosphere to reach beyond the horizon, while higher frequencies travel mainly in straight, line-of-sight paths but carry more data.

Radio frequency technology:
Bluetooth
Digital modulation	GPS	RF datacommunication	UMTS
EMW	GSM	Transmission lines	WAP
GPRS	Radio frequency	Transmission lines topics	WIFI-WLAN

Electro magnetic waves

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