What is the definition of an antenna?

An antenna (antenna) is a transducer that transforms a traveling wave propagating on a transmission line into an electromagnetic wave propagating in a unbounded medium (usually a free space), or in reverse. A component used in radio equipment to transmit or receive electromagnetic waves. Radio communications, radio, television, radar, navigation, electronic confrontation, remote sensing, radio astronomy and other engineering systems, all the use of electromagnetic waves to transmit information, rely on the antenna to work. In addition, in the use of electromagnetic waves to transmit energy, not signal energy radiation also needs the antenna. General antennas are reversible, that is, the same pair of antennas can be used as a transmitting antenna, but also used as a receiving antenna. The same day line is the same as the basic parameters for transmitting or receiving. This is the reciprocity theorem for antennas.

Classification of antennas:

① according to the nature of work can be divided into transmitting antenna and receiving antenna.

② According to the use can be divided into communication antennas, broadcast antennas, television antennas, radar antennas and so on.

③ by working wavelength can be divided into super long wave antenna, long wave antenna, MW antenna, shortwave antenna, ultrashort antenna, microwave antenna and so on.

④ according to the structure and working principle can be divided into line antennas and surface antennas. The characteristic parameters of the antenna include directional graph, directivity coefficient, gain, input impedance, radiation efficiency, polarization and frequency width.