An antenna is a converter that converts the guided waves transmitted on a transmission line or vice versa. A component used in radio equipment to transmit or receive electromagnetic waves.
Definition of antenna:
Radio communication, broadcasting, television, radar, navigation, electronic countermeasures, remote sensing, radio geography and other radio equipment all transmit information through radio waves, which require the radiation and reception of radio waves.
Therefore, the equipment used to radiate and receive radio waves in radio equipment is called antenna.
The antenna provides the required coupling between the transmitter or receiver and the medium that transmits radio waves. Like transmitter and receiver, antenna is an important part of radio equipment.
Anyone who uses electromagnetic waves to transmit information depends on the antenna for operation.
In addition, in terms of transmitting energy with electromagnetic waves, antenna is also required for non signal energy radiation. Generally, antennas are reversible, that is, the same pair of antennas can be used as both transmitting and receiving antennas. The basic characteristic parameters of the same antenna for transmission or reception are the same. This is the reciprocity theorem of antenna.
Functions of antenna:
The antenna radiates radio waves and receives radio waves. However, what the transmitter sends to the antenna through the feeder is not radio waves, and the receiving antenna cannot send radio waves directly to the receiver through the feeder, which must go through the process of energy conversion.
Classification:
1. According to the nature of the operation, it can be divided into transmitting antenna and receiving antenna.
2. It can be divided into communication antenna, broadcast antenna, TV antenna, radar antenna, etc.
3. According to directivity, it can be divided into omnidirectional antenna and directional antenna.
4. According to the operating wavelength, it can be divided into ultra long wave antenna, long wave antenna, medium wave antenna, short wave antenna, ultra short wave antenna, microwave antenna, etc.
5. According to the structure and operation principle, it can be divided into wire antenna and plane antenna. The characteristic parameters describing the antenna include pattern, directivity coefficient, gain, input impedance, radiation efficiency, polarization and bandwidth.
6. According to the dimension, it can be divided into two types: one-dimensional antenna and two-dimensional antenna.
7. Antennas can be divided into three categories according to different applications: handheld station antenna, vehicle antenna and base antenna.
Common antenna:
Base station antenna, repeater antenna and indoor antenna commonly used in mobile communication.
