In communication, different ways are used to transport the electrical signal from the transmitter to the receiver.
Electromagnetic waves consist of electric and magnetic fields, which are inseparable. An electric field varying in time produces a space-time varying magnetic field, which, in turn, produces electric field. This mutually supporting role results in propagation of electromagnetic waves according to e.m. laws.
E = Eo sin(kz – ωt)
H = Ho sin(kz – ωt)
The direct experimental evidence for the existence of e.m. waves came in 1888 through a series of experiments by Hertz. He found that he could detect the effect of e.m. induction at considerable distances from his appparatus. By measuring the wavelength and frequency of e.m. waves, he calculated their speed, which was equal to the speed of light. He also showed that e.m. waves exhibited phenomena similar to those of light.
In 1895, Indian physicist Jagadis Chandra Bose produced waves of wavelength in the range 25 mm to 5 m and demonstrated the possibility of radio transmission. This work was put to practical use by Guglielmo Marconi who, succeeded in transmitting e.m. waves across the Atlantic Ocean. This marked the beginning of the era of communication using e.m. waves.
In a communication system, a transmitter radiates electromagnetic waves with the help of an antenna. These waves propagate in the space and captured by the receiver. At the receiver, another antenna extracts energy (in formation) from the electromagnetic waves.