The definition of antenna
We know that communications, radar, navigation, radio, television and other radio devices are all transmission of information through radio waves, which require radiation and reception of radio waves. In radio equipment, a device for radiating and receiving radio waves is called an antenna. Antennas provide the necessary coupling between transmitter and receiver and medium for transmitting radio waves. Antennas, like transmitters and receivers, are also an important part of radio equipment.
The function of the antenna
The antenna radiates radio waves and receives radio waves. However, the transmitter is not a radio wave sent through the feeder to the antenna. The receiving antenna can not send the radio wave directly through the feeder into the receiver, and the energy conversion process must be passed. Next, we take the radio communication equipment as an example to analyze the transmission process of the signal, and then illustrate the energy conversion function of the antenna.
Working principle
When a conductor passes through a high frequency current, an electric field and a magnetic field will be generated in the surrounding space. According to the distribution characteristics of electromagnetic field in space, it can be divided into near area, middle area and far area. Let R be the distance from the conductor to the space, and the region at a is called the near area. The electromagnetic field in the area is closely related to the current and voltage in the conductor. The region of the B is called a far zone. In this area, the electromagnetic field can leave the conductor to spread to the space. Its change is lagging behind the current and voltage on the conductor for a period of time. At this time, the electromagnetic wave propagating out has no direct connection with the current and voltage on the wire, and the electromagnetic field in this region is called the radiation field. It must be pointed out that when the length of the wire is much smaller than the wavelength of wavelength, the radiation is very weak; when the length of the conductor is L increases to the length of the conductor, the current on the wire will increase greatly, and thus the stronger radiation can be formed.
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