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Antenna electromagnetic radiation |
| Author： Date：2016/7/27 10:55:24 |
The function and position of antenna
Radio transmitter output radio frequency signal power, through the feeder (cable) to the antenna, the antenna in the form of electromagnetic radiation to go out. After arrival at the receiving site, the electromagnetic wave is received by the antenna (only a small fraction of the power is received), and is sent to the radio receiver via the feeder. It is seen that the antenna is an important radio equipment to transmit and receive electromagnetic waves. Antenna variety, for different frequencies, different uses, different occasions, different requirements, such as the use of different circumstances. For many varieties of antenna, proper classification is necessary: according to the purpose of the classification, can be divided into communication antenna, TV antenna, radar antenna; according to the working frequency band classification, can be divided into short wave antenna, ultra short wave antenna and microwave antennas; according to the direction of classification, can be divided into omni-directional antenna and directional antenna; according to shape classification, can be divided into linear antenna, planar antennas.
Electromagnetic wave radiation
When there is an alternative current flowing on the conducting wire, the electromagnetic wave can be radiated, and the capability of the radiation is related to the length and shape of the conductor. As shown in Figure 1.1 A., if two wire distance is very near, the electric field is bound between the two wires, and the radiation is weak; the two wires open, as shown in Figure 1.1 B shows, electric field spread around in space, so the radiation enhancement. It must be pointed out that, when the wire length L is much smaller than the wavelength lambda, the radiation is weak; the length L of the wire increases to comparable with the wavelength, will greatly increase the current on the wire and can, therefore, the formation of strong radiation. |