Antenna is a converter that transforms a conductive wave traveling over a transmission line into an electromagnetic wave that travels in a boundaryless medium (usually free space), or does the opposite. A component used in a radio device to emit or receive electromagnetic waves. Radio communication, radio, television, radar, navigation, electronic confrontation, remote sensing, radio astronomy and other engineering systems, all the use of electromagnetic waves to transmit information, all rely on antennas to carry out work. In addition, in the use of electromagnetic waves to transmit energy, non-signal energy radiation also requires antennas. General antennas are reversible, i.e. the same antenna can be used as both a transmitter and a receiving antenna. The basic characteristic parameters of the same antenna as transmission or reception are the same.
Antenna radiation is radio waves, receiving also radio waves, however, the transmitter through the feeder into the antenna is not radio waves, the receiving antenna can not send radio waves directly through the feeder to the receiver, which must go through the energy conversion process. Let's take radio communication equipment as an example to analyze the transmission process of the signal, and then explain the energy conversion of the antenna.
At the transmitter, the modulated high-frequency oscillation current (energy) generated by the transmitter is fed into the transmitting antenna (the feed device can transmit current waves or electromagnetic waves directly depending on the frequency and form), and the transmitting antenna converts the high-frequency current or conduction wave (energy) into radio wave-free electromagnetic wave (energy) to the surrounding space radiation (see Figure 1); From the above process, it can be seen that the antenna is not only a device that radiates and receives radio waves, but also an energy converter, which is an interface device between circuit and space.