An antenna is a transducer that converts radio frequency (RF) fields into alternating current or vice versa. There are both receiving and transmission antennas for sending or receiving radio transmissions. Antennas play an important role in the operation of all radio equipment. They are used in wireless local area networks, mobile telephony and satellite communication.

Antennas have an arrangement of metallic conductors with an electrical connection to receivers or transmitters. Current is forced through these conductors by radio transmitters to create alternating magnetic fields. These fields induce voltage at the antenna terminals, which are connected to the receiver input. In the far field, the oscillating magnetic field is coupled with a similar oscillating electric field, which defines electromagnetic waves capable of propagating the signal for long distances. 

Radio waves are electromagnetic waves that carry signals through air at the speed of light without any transmission loss. Antennas can be omni-directional, directional or arbitrary.

The main function of an antenna is to receive and transmit electromagnetic waves.
The radio frequency signal power output by the radio transmitter is transmitted to the antenna through the feeder (cable) and radiated out by the antenna in the form of electromagnetic waves. When the electromagnetic wave reaches the receiving point, it is followed by the antenna (which receives only a very small part of the power) and sent to the radio receiver through the feeder. It can be seen that antenna is important to radio equipment for transmitting and receiving electromagnetic waves. Without the antenna, there would be no radio communication.

Antenna usage area:

Antenna applications for multi-polarized antennas include mining and agriculture networks, indoor and outdoor deployments, automatic guided vehicles (AGVs), unmanned systems, transit and rail, and HAM radio and scanners. Land mobile radio, mobile data, and DAS and BDA are also common antenna applications.