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What is antenna polarization? Why do we need to consider antenna polarization?

Author:Xia Men Lineyi Antenna & Connector Click: Time:2020-08-08 16:52:38

What is antenna polarization? Why do we need to consider antenna polarization?

Antenna polarization is similar to optical polarization. Although there is a "polar", it has nothing to do with Arctic weather, but involves sending and receiving electromagnetic radiation according to the direction of electromagnetic radiation. Through optical polarization, film or glass can block light that is polarized in a certain direction (that is, become darker), while allowing light with the correct polarization to pass through. This is similar to an antenna-the polarization of the antenna determines its electromagnetic radiation transceiver performance.

Polarization is based on the oscillation plane of the electric field component of electromagnetic radiation. If the polarization of the electromagnetic wave is cancelled by the antenna polarization rotation, the antenna can only capture a part of the electromagnetic wave. Therefore, if the transmitting antenna and the receiving antenna use the same plane as the reference plane, in order to achieve the best efficiency of the communication link, their polarization directions should be the same. For some applications, the choice of polarization direction can also rely on other physical phenomena.

Although there are many types of polarization, there are mainly three. The radio frequency antenna is usually a linear polarization or a circular polarization antenna. Linearly polarized antennas are usually vertically polarized or horizontally polarized antennas, while circularly polarized antennas are left-handed or right-handed circularly polarized antennas. In addition, there is a common type of polarization that is elliptical polarization formed by a complex combination of linear polarization and circular polarization.

The polarization loss of the linear polarization system depends on the angle between the linear polarization antenna and the polarization vector of the electromagnetic wave, and the maximum polarization loss occurs when the two are at an angle of 45 degrees. Under the polarization vector deflection angle of 45 degrees, the maximum polarization loss is 0.5 (that is, 3dB). In the case of circular or elliptical polarization systems, the calculation of polarization loss is more complicated, and the maximum polarization loss can be as high as 30dB. 

This is why polarization can be used to achieve signal isolation and interference can occur between antenna systems. Although there is polarization loss, antennas that are polarized in different ways can still receive signals from electromagnetic waves with different polarization types. Therefore, the signal isolation effect that can be achieved by polarization has a certain limit.

Under normal circumstances, the antenna polarization mode can be selected according to application requirements. Different applications can obtain better results from different polarization methods. For example, because vertically polarized electromagnetic waves are easier to pass through uneven terrain than horizontally polarized electromagnetic waves, vertically polarized antennas have better performance in land mobile communications applications, while horizontal polarization depends on the ionosphere and is usually long. It performs better in the use of distance communication. In addition, since circular polarization can usually better alleviate the weakening caused by satellite directional deviation, circular polarization is often used in satellite communications.

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