Why Must We Consider Antenna Polarization?

  • Source: eahison
  • Date:08/19/2019

Antenna polarization is similar to optical polarization, although it has a "pole" word, but it has nothing to do with the Arctic weather, but involves transmitting and receiving electromagnetic radiation according to the direction of electromagnetic radiation. By optical polarization, film or glass blocks light that is polarized in a certain direction (becomes darker) while allowing the correct polarization of light to pass. This is similar to an antenna - the polarization of the antenna determines its electromagnetic radiation transceiving performance.

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


Although there are multiple types of polarization, there are three main types. The RF antenna is typically a linearly polarized or circularly polarized antenna. Linearly polarized antennas are typically 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 an elliptical polarization formed by a complex combination of linear polarization and circular polarization.


The polarization loss of a linearly polarized system depends on the angle between the linearly polarized antenna and the polarization vector of the electromagnetic wave, and the maximum polarization loss occurs at an angle of 45 degrees between the two. At a polarization vector deflection angle of 45 degrees, the maximum polarization loss is 0.5 (i.e., 3 dB). In the case of a circularly or elliptically polarized system, the calculation of polarization loss is more complicated and the maximum polarization loss can be as high as 30 dB. This is why polarization can be used to achieve signal isolation and interference between antenna systems. Although polarization losses exist, antennas polarized in different ways can still receive signals from electromagnetic waves of different polarization types. Therefore, the signal isolation effect that polarization can achieve has a certain limit.


Under normal circumstances, the antenna polarization mode can be selected according to the application requirements. Different applications can achieve better results from different polarizations. For example, vertically polarized antennas perform better in terrestrial mobile communications applications because vertically polarized electromagnetic waves are more likely to pass through undulating topography than horizontally polarized electromagnetic waves, while horizontal polarization is dependent on the ionosphere and is usually long. It performs better in the use of communication. In addition, circular polarization is often used for satellite communications because circular polarization generally mitigates the degradation caused by satellite orientation shifts.

 

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