What is Antenna Polarization and Why It Matters

Polarization is an important phenomenon that is useful in different analyses of electromagnetic (EM) waves. Understanding polarization plays a significant role in maximum signal transmission. Maximum signal transmission is the event where the signal’s fidelity is preserved during the transmission. To achieve maximum signal transmission, the transmitter and receiver antenna elements must maintain the same antenna polarization. In the case when there is no match in polarization the signal strength will be reduced.

In this article, we will discuss the importance of understanding antenna polarization. This includes discussing a brief history of polarization, types of antenna polarization, and factors affecting polarization. Furthermore, we will explore some of the applications of antenna polarization and how they are utilized across different domains. This article can serve as a brief and concise comprehensive guide for antenna polarization.

Basics of Antenna Polarization

An EM wave consists of two perpendicular fields. These fields are:

• Electric field (E-field)
• Magnetic field (H-field)

These two fields are perpendicular to each other and the direction of the wave’s propagation. Antenna polarization is defined based on the electric field’s orientation. Accordingly, we can define antenna polarization as the orientation of the E-field of the EM wave radiated by the transmitter antenna. This is an important concept, as the E-field is important when we consider the strength of the signal.
When it comes to the history of antenna polarization, James Maxwell is one of the most influential scientists, who formulated Maxwell’s equations to describe the EM wave propagation and interaction between E-field and H-field. However, it was Heinrich Hertz who experimentally demonstrated polarization using a dipole antenna in the late 1880s.

Having a brief understanding of the definition of antenna polarization, and the history of antenna polarization, is necessary to understand the fundamental relationship between antenna polarization and EM waves. Fundamentally, antenna polarization can affect the EM waves,

• Signal strength at the receiving end
• Signal interference level due to multipath interference and polarization mismatch

Apart from these two fundamental ideas, polarization can also largely limit antenna design. Therefore, it is necessary to have a proper understanding about antenna polarization before an antenna design.

Types of Antenna Polarization

There exist several types of antenna polarization modes depending on different circumstances which would depend on environmental conditions and antenna designs. Moreover, depending on the advantages and disadvantages of each type of antenna polarization they are used in different forms of wireless communication media.

There are three main types of antenna polarization, namely,

1. Linear polarization
2. Circular polarization
3. Elliptical polarization

Horizontal and Vertical polarization

Dual slant polarization

Linear Polarization

Linear polarization is the most frequent type of polarization that we can see in practical applications. In linear polarization, all radiation that is being transmitted will be confined to one plane. Simply, here the E-field will only oscillate in a single direction. Depending on the direction of the E-field’s oscillation, there are three linear polarization sub-categories. They are:

• Horizontal polarization – Here the E-field oscillates from side to side and can be picked up by horizontal elements of an antenna.
• Vertical polarization – Here the E-field oscillates up and down and can be picked up by vertical elements. A significant advantage of using vertical polarization is that it radiates equally around the horizontal plane.
• Slanted polarization – Here the E-field oscillates at an angle to either a horizontal or vertical plane. Slanted polarization can be picked up by both horizontal and vertical elements of an antenna.

Circular Polarization

Here, the E-field will rotate while the signal propagates. This is a complex form of polarization when compared to linear polarization, which is widely used in satellite communication applications. Furthermore, for circular polarization to occur, three conditions are necessary to be satisfied. They are:

• The E-field must have two orthogonal vector components
• These vector components should be 90 degrees out of phase
• These vector components should be equal in magnitude

Depending on the direction of rotation of the E-field there are two types of circular polarization, namely:

• Right-hand Circular polarization (RHCP)
• Left-hand Circular polarization (LHCP)

Elliptical polarization

Elliptical polarization is a mix of both linear and circular polarization. This mix is due to the mismatch of the magnitude of E-field orthogonal vector components that we described previously in circular polarization. Like circular polarization, elliptical polarization is widely used in satellite communications as well as in Radar systems.

Factors Influencing Antenna Polarization

Several factors can influence antenna polarization since the EM waves are propagated freely in space. However, we can narrow down a few key factors that can have a substantial influence on antenna polarization. These factors are:

• Environmental factors: Here the terrain is a major concern. Depending on the nature of the terrain, i.e., urban, rural, etc., the degree of polarization is affected due to signal reflection, diffraction, and scattering. Furthermore, obstacles present in the environment can interact with the signal through reflection and absorption.
• Frequency: The transmission frequency will determine the degree of polarization, where higher frequencies are more susceptible to polarization.
• Antenna design: The antenna size, shape, orientation, and different elements also can affect polarization as they determine how the signal is received and transmitted.
• Signal propagation considerations: Other factors like atmospheric conditions, and channel distortions can also affect polarization.

Applications of Antenna Polarization

Having a comprehensive idea about antenna polarization, now let us investigate some of the widely used applications of antenna polarization. When it comes to wireless communication systems, polarization is used to reduce interferences that may occur during the progress of transmission. Moreover, achieving desirable polarization will increase the clarity of the signal and strength of the signal. Finally, in wireless communication systems such as cellular networks, polarization is used to increase channel capacity by achieving different flavors of polarization within the same channel. Also, in RFID systems polarization can be an influential factor in determining the read range of RFID systems due to interferences in the environment.

Furthermore, circular polarization and elliptical polarization are widely used in satellite and Radar systems due to the high degree of interference in these systems. In the case of satellite communication, introducing circular polarization can effectively compensate for the signal distortion that may occur due to the rotation of the satellites. Moreover, these two types of polarization can also be used to study the motion of large celestial bodies in radio astronomy.

Polarization diversity

Polarization diversity is a special case of polarization where multiple versions of a signal are transmitted and received by using several types of polarization. This is useful in mitigating polarization mismatch as the signal will be received in different types of polarizations. Moreover, it will also reduce signal degradation due to multipath interference.

This technique is useful in MIMO systems as it will reduce the size of MIMO terminal stations and the number of MIMO antennas. Such an advantage is achieved by using several types of polarized signals and low correlations between them. However, despite the advantage of polarization diversity, achieving such functionality will increase the cost of the overall system.

Practical Considerations for Antenna Polarization

Finally, let us understand some important practical considerations we need to consider in utilizing antenna polarization. The major factors can be summarized as follows:

• Proper alignment and orientation: This is a crucial factor to be considered as it will affect the signal clarity and strength. Moreover, great care should be taken when using directional communication links.
• Mitigation of polarization mismatch: Polarization mismatch can eventually cause failure in the reception of the correct signal. Therefore, we can use techniques such as polarization diversity and adaptive polarization.
• Antenna selection criteria: For example, vertical polarization is preferred in hand-held mobile radios, hence the dipole antenna is mounted vertically. Moreover, wire antennas can be used in High-frequency range, and for higher frequency polarized signals linear polarization methods are used.

Future Trends and Developments

With the advancements in 5G and 6G communication, we can see an increase in research in adaptive polarization techniques and the use of machine learning techniques in wireless communications. Moreover, research in intelligent reflective surfaces for adaptive antennas is another emerging research area in the industry. These research trends can contribute to emerging communication systems facilitating IoT (Internet of Things) applications, drone communications, and vehicular networks.

Conclusion

In conclusion, we can see that polarization is an important concept we need to understand to deal with applications involving antennas and communication systems. In this article, we discussed the importance of antenna polarization, the different types, and their applications. This short article can be used as a reference for understanding the concept of polarization.