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Antenna 4 kinds of self-contained basic function detailed explanation
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For the antenna, we understand a variety of knowledge has been a lot, but for the antenna thing, we except from its basic information to explain, in fact, ignore its existence of meaning. Why do we need antennas, just because of the transmission of data? It is much more than that. This article will focus on the 4 basic functions of antenna, from the original point of view, to analyze the meaning of using antenna.
We all know that all radio equipment (including radio communication, radio, TV, radar, navigation and other systems) use radio waves to work, and the transmission and reception of electromagnetic waves from tens of MHz ultra-long wave to more than 40 GHz millimeter band are realized through antennas. Antenna is such a component, for transmitting, it will be the circuit of high-frequency current or feed transmission line on the guide line wave effectively converted into some kind of polarization of space electromagnetic wave, to the specified direction to launch out; for receiving, will be from the space of a specific direction of some kind of polarization of electromagnetic wave effectively converted into the circuit of high-frequency current or transmission line on the guide line wave.
To sum up, the antenna's own basic function has four main points.
First, energy conversion
For the transmitting antenna, the antenna should be the high-frequency current energy in the circuit or transmission line on the guided wave energy as much as possible to convert the space electromagnetic wave energy radiation out. For the receiving antenna, the antenna should be received by the maximum conversion of electromagnetic wave energy into the circuit of high-frequency current energy delivered to the receiver. This requires the antenna and the transmitter source as good a match as possible, or as good a match as possible with the receiver load. Good antenna, is a good energy converter.
Second, directional radiation or receive
For the transmitting antenna, the radiation of electromagnetic wave energy should be concentrated in the specified direction as far as possible, and in other directions not radiation or radiation is very weak. For receiving antenna, only receive the electromagnetic wave from the specified direction, in the other direction receiving ability is very weak or do not receive.
For example, in the case of radar, its task is to search and track a specific target. If the radar antenna does not have a sharp directional, it can not identify and determine the location of the target. And if the antenna is not directional, or directional weak, then for the transmitting antenna, only a small part of the energy it radiates reaches the specified direction, most of the energy is wasted in the unwanted direction. For the receiving antenna, in receiving the required signal at the same time, will also receive from the other direction of the interference signal or noise signal, resulting in the required signal completely submerged in interference and noise. Therefore, a pair of good antenna should have a certain task to complete the required direction.
If we want to receive satellite TV and other signals, due to the distance, it is necessary to use a good directional, high gain antenna, such as rotating parabolic antenna, Cassegrain antenna, array antenna, etc.
Third, there should be the appropriate polarization
That is, the antenna transmits or receives the polarization of electromagnetic waves. For example, a vertical polarization of the antenna, can not receive the horizontal polarization of the incoming wave, and vice versa; a left circular polarization of the antenna can not receive the right circular polarization of electromagnetic waves, and vice versa. A circularly polarized antenna to the line polarization of the incoming wave will have half energy loss.
Fourth, the antenna should be enough band width
Any antenna has a certain working band. In this band range outside of its work failure.
A pair of antennas and sending and receiving is reciprocal. According to the principle of reciprocity in electromagnetism can prove that, as long as the antenna and feed network does not contain nonlinear devices (such as ferrite devices), the same antenna used for transmitting and receiving, the basic characteristics remain unchanged. Therefore, when analyzing the characteristics of the receiving antenna, you can use the method of analyzing the transmitting antenna.
