What is the Polarization? Using Antenna Polarization as an Example
What is the polarization? In this article, we use antenna polarization as an example, to deeply explain the key concept of antenna polarization. That is akin to the "signature" of an antenna, having a crucial impact on wireless communications!
What is antenna polarization?
In the realm of wireless communication, antennas act as "couriers" of signals, and antenna polarization is its "unique method" of delivering signals. Simply put, the affective polarization direction of an electromagnetic wave is the vertical direction of the antenna's polarization, mainly divided into three types: linear polarization, circular polarization, and elliptical polarization. It's akin to how couriers handle packages: some hold them vertically (vertical polarization), others horizontally (horizontal polarization), and some spin them around (circular polarization).
Antenna polarization is a critical factor in antenna design, installation, and integration within wireless communication systems. Different antennas exhibit distinct polarization characteristics, directly affecting their "compatibility" with signals. Theoretically, polarization refers to the plane of electromagnetic wave vibration, and antennas are highly "sensitive" to this plane, typically favoring signals with specific polarization. Much like people excel in fields they are familiar with, antennas are adept at receiving or transmitting signals that match their basis polarization type.
Most antennas' polarization can be easily determined as it aligns with the plane where the antenna elements reside. For instance, a vertical antenna stands upright like a "straight-standing courier," adept at receiving vertically polarized signals; a horizontal antenna lies flat like a "supine courier," more attuned to horizontal polarized signals.
The matching of antenna polarization with signal polarization is crucial, akin to the relationship between a key and a lock – only a proper match ensures maximum efficiency. If mismatched, the signal strength diminishes significantly, as using the wrong key fails to unlock the door, reducing signal strength by the cosine of their angle. Ideally, in free space, the polarization directions of antennas and signals should align perfectly; if perpendicular, theoretically, no signal would be received.
In ground-based radio communication, once emitted, the signal's polarization direction remains relatively stable, but reflections from objects along the path can disrupt it, altering the signal's polarization state. The signal ultimately received is a "mélange" of direct and numerous reflected signals, maintaining an overall polarization direction with slight nuances.
Types of antenna polarization
The world of polarization is diverse, offering varied "postures" for signal transmission, each with unique traits and applicable scenarios.
Linear Polarization: The most "simple" signal transmitter
● Linear polarizer is the most common form of polarization axes, characterized by all radiation occurring within a single plane, resembling a straight road where signals travel in a fixed vertical direction.
● Horizontal Polarization: Antennas with a horizontal "framework," specifically "capturing" and radiating horizontal polarized signals, akin to a conveyor belt placed horizontally, conveying signal packages in a particular direction.
● Vertical Polarization: Represented by vertical elements, akin to an erect flagpole, capable of evenly radiating signals within the horizontal single plane, featuring low radiation angles, allowing most energy to propagate near the ground, particularly suitable for automotive installations, acting as a tailored signal "receiver" for cars.
● Slant Polarization: Angled with respect to horizontal or vertical planes, like a tilted conveyor belt, enabling both vertical and horizontal polarized antennas to "get work," increasing signal reception potential.
Circular Polarization: A "reliable assistant" in satellite communication
● Circular polarization offers unique advantages in magnetic fields like satellite communication, effectively addressing anomalies in direction of propagation, ground reflection, and satellite spin-related issues. Imagine signals emanating from a rotating antenna, with the tip of the electric field vector spiraling like a helix, creating a vivid image!
● Right-Hand Circular Polarization: Vectors rotate in the direction of tightening a bottle cap with the right hand.
● Left-Hand Circular Polarization: The opposite of right-hand circular polarization, vectors rotate leftward.
Mixed Polarization (Elliptical Polarization): A "fusion style" of linear and circular polarization
When linear and circular polarizations "mix," elliptical polarization forms. The tip of the electric field vector traces an ellipse, akin to dancing a unique dance. Interestingly, linear and circular polarized antennas can "guest star" in receiving each other's signals, though the signal strength reduces by 3dB, as if using a less familiar method to deliver packages, reducing efficiency slightly.
Applications of Different Types of Antenna Polarization
Different polarization types play unique roles in their respective fields, much like how different couriers excel on various delivery routes.
● General Radio Communication:Linear polarization, known for its simplicity and straightforwardness, acts as the "workhorse" for most radio communications. It’s like the typical courier efficiently delivering signals using conventional methods.
● Mobile Phones and Short-Distance Wireless Communication:With the rapid development of mobile phones and short-distance wireless communication, linear polarization has become a common choice due to the ease of antenna manufacturing. For instance, mobile phones and Wi-Fi routers often use vertical polarization, though some router antennas are adjustable. Additionally, because signals undergo multiple reflections during transmission, resulting in random polarization upon reaching the receiver, polarization matching becomes less critical.
● Mobile Two-Way Radio Communication:Traditional mobile two-way radio communications, such as emergency services and vehicle-mounted radios, mostly employ vertical polarization. Vertical polarized antennas have an omnidirectional radiation pattern, like a courier with a 360-degree coverage. They allow stable signal reception without needing to adjust the antenna direction as vehicles move.
● Long-Distance HF Ionospheric Communication:Both horizontal and vertical polarizations show their strengths. Horizontal polarized wire antennas are easy to erect using poles, and large multi-element antenna arrays are more conveniently installed on a horizontal plane. Meanwhile, vertically polarized single-element antennas leverage low radiation angles to achieve excellent long-distance transmission and reception.
● Medium Wave Broadcasting:Medium longitudinal wave radio stations favor vertical polarization because vertically polarized ground waves propagate better along the Earth's surface. The simple structure of a vertically polarized antenna, requiring only a single vertical element, offers advantages over horizontally polarized antennas.
● Satellite Communication:Circular polarization shines in satellite communication, effectively overcoming direction of propagation challenges and mitigating fading caused by changes in satellite orientation, ensuring stable signal transmission.
Though invisible and intangible, antenna polarization acts as a "behind-the-scenes hero" in the realm of wireless communication, playing a crucial role in various application scenarios.
Polarization Matching
Understanding the concept of antenna polarization makes grasping polarization matching relatively straightforward. In essence, polarization matching occurs when the receiving antenna and the transmitting antenna share the same polarization and rotational characteristics. This alignment enables the receiving antenna to capture all the energy radiated by the transmitting antenna, maximizing signal transmission. It is akin to using the right key for a lock – only the "key" of polarization characteristics can unlock the door to seamless signal transmission, allowing signals to flow unimpeded.
For example, in linear polarization, if the transmitting antenna emits a horizontally polarized wave, the receiving antenna must also be set to horizontal polarization to achieve optimal signal reception. If the receiving antenna uses vertical polarization instead, it’s like trying to use the wrong key, unable to unlock the "lock" of signal transmission, which will considerably decrease the efficiency of signal transfer, potentially preventing signal reception altogether. Such polarization mismatch resembles a communication barrier between two people speaking different languages; they cannot understand each other, and information exchange is inevitably obstructed.
In practical communication systems, polarization matching plays a crucial role in ensuring stable signal transmission. In satellite communications, given the vast distances between satellites and ground stations, signals face various influencing factors during transmission, such as atmospheric interference and multipath effects. To guarantee accurate and stable signal transmission, both satellite and ground station antennas must achieve good polarization matching. Only then can ground stations receive the faint signals emitted by satellites and extract useful information from them. Without polarization matching, signals suffer significant attenuation during transmission, leading to degraded communication quality or even complete disconnection.
The Role of Polarization Matching
Polarization matching assumes a pivotal role in the entire communication system, directly affecting the efficiency and quality of signal transmission. When the transmitting and receiving antennas achieve polarization matching, it creates an unrestricted expressway for the signal, enabling efficient transmission from the sender to the receiver. At this point, the receiving antenna can optimally capture the energy radiated by the transmitting antenna, bringing the signal strength to its peak state. In mobile communications, polarization matching between cell phone antennas and base station antennas is essential. Only when their polarization modes align can the phone receive sufficiently strong signals to ensure clear and smooth calls and fast, stable network connections. If polarization is mismatched, signal strength sharply declines, leading to poor call quality, network lag, or even disconnection.
Polarization matching is also closely related to the anti-interference capability of communication systems. In complex electromagnetic environments, various interfering signals exist, often having polarization modes different from those of useful signals. By achieving polarization matching, the receiving antenna can effectively suppress these interfering signals, improving the signal-to-noise ratio and enhancing the communication system's resistance to interference. In radar systems, polarization matching technology is widely used to distinguish target echoes from interference signals. Given that different targets and interference sources possess distinct polarization characteristics, radar can accurately identify target echoes and suppress ground clutter, weather interference like rain or snow, and human-made interference by designing specific polarization reception methods, thereby improving target detection accuracy and reliability.
From a broader perspective, polarization matching plays an indispensable role in optimizing the performance of entire communication systems. As modern communications evolve, with increasing data transmission demands and rising quality standards, the significance of polarization matching technology becomes ever more prominent. It not only boosts signal transmission efficiency and stability but also supports the expansion of communication system capacity and coverage. In constructing 5G networks, the application of polarization matching technology aids in achieving high-speed, high-capacity data transmission, meeting user demands for high-definition video, virtual reality, and other services, thus propelling communication technology to higher levels.
Methods of Achieving Polarization Matching
Achieving polarization matching isn't instantaneous; it requires a comprehensive application of various methods to ensure optimal signal transmission effects across different communication scenarios. When selecting an appropriate polarization mode, one must thoroughly consider the communication system's requirements, environmental conditions, and antenna design factors. If a communication system specifies a particular polarization requirement, such as circular polarization in some satellite communication systems, the corresponding antenna polarization mode must strictly follow these system requirements. In open areas or spaces far from reflectors, linearly polarized antennas are often ideal due to their simple structure and minimal signal transmission loss. However, in urban environments or complex propagation settings, where numerous buildings and terrain features act as reflectors causing severe multipath effects and scattering, circularly polarized antennas hold an advantage, effectively reducing multipath interference to ensure stable signal transmission.
Adjusting the antenna direction is a critical step in achieving polarization matching. In practice, the receiving antenna's direction must be precisely adjusted based on the transmitting antenna's position and signal propagation direction, aligning their polarization directions as closely as possible. For terrestrial satellite communications, operators use specialized equipment, like satellite antenna alignment tools, to accurately measure the satellite's azimuth, elevation, and polarization angles, then adjust the ground receiving antenna to the corresponding angles to achieve polarization matching with the satellite antenna. This process demands high precision since even minute deviations can degrade signal reception quality.
Employing polarization diversity techniques is another effective means of achieving polarization matching. Polarization diversity utilizes the uncorrelated fading characteristics of signals emitted from antennas with orthogonal polarization directions at the same location for diversity reception. Currently, dual-polarized antennas commonly adopt ±45° dual-linear polarization, equipping transmit and receive terminals with ±45° polarized antennas. This setup allows the acquisition and polarization diversity of two signal paths with uncorrelated fading characteristics. In mobile communication base stations, polarization diversity technology frequently enhances signal reception quality. By simultaneously receiving horizontally and vertically polarized signals and processing and merging these two signals, the impact of signal fading can be effectively reduced, improving communication reliability and stability.
Factors Influencing Polarization Matching
In real-world communication environments, maintaining ideal polarization matching is challenging due to the influence of multiple factors that act as hidden "sources of interference," continually testing the stability and reliability of communication systems.
Environmental factors significantly impact polarization matching. In urban environments filled with skyscrapers, these structures function as giant mirrors, reflecting and refracting electromagnetic waves as they propagate. When signals encounter buildings, they reflect in various directions, creating multipath propagation. Consequently, the received signal comprises multiple paths with different polarization directions. Originally transmitted as a single polarized signal, its polarization may transform into a complex variety after multipath propagation, making it difficult for the receiving antenna to achieve perfect polarization matching with the transmitting one. In mountainous areas with rugged terrains, topographical undulations also noticeably affect electromagnetic wave propagation. Mountains can cause signal diffraction, while valley formations might focus or scatter signals; both scenarios alter signal polarization characteristics, complicating polarization matching.
Reflection and refraction phenomena during signal propagation also significantly influence polarization matching. When electromagnetic waves transition between media, refraction occurs, changing the direction of the electric field vector according to Snell's law. For instance, if a horizontally polarized wave encounters a medium like water with a certain dielectric constant, refraction can tilt the electric field vector away from pure horizontal polarization. Such changes in polarization direction lead to mismatches between the transmitting and receiving antennas, diminishing signal reception intensity. Similarly, reflection alters polarization direction. When electromagnetic waves reflect off metal objects or strong reflectors, the reflected light wave's polarization may differ from the incident transverse wave, creating cross-polarization components. These cross-polarization components act as interference signals within communication systems, hampering the receiving antenna's ability to capture the primary signal and degrading polarization matching quality.
Antenna design and performance are also tightly linked to polarization matching. Different antennas exhibit unique polarization characteristics, influenced by factors like structure, size, and shape, impacting polarization mode and purity. A poorly designed antenna might produce significant cross-polarization components, complicating effective polarization matching with the transmitting antenna even in ideal conditions. Manufacturing errors can cause performance deviations from design expectations, affecting polarization matching outcomes. Moreover, antenna aging and damage alter polarization properties, impacting matching. Prolonged exposure to harsh environmental conditions—such as wind erosion, rainfall, and UV radiation—can degrade antenna materials, causing polarization drift and reducing matching precision.
Applications of Polarization Matching
Polarization matching technology finds extensive and profound applications across various fields, acting as an "invisible link" within communication systems, quietly supporting the efficient operation of diverse communication equipment, and significantly enhancing convenience in daily life and work.
In satellite communication, the importance of polarization matching is self-evident. Communication between satellites and ground stations spans great distances, with signals subject to complex factors like atmospheric interference, multipath effects, and ionospheric variations during transmission. To maintain stable and precise signal transmission, satellite and ground station antennas must achieve excellent polarization matching. In geostationary satellite communications, satellites typically adopt specific polarization modes for signal transmission, while ground stations must accurately adjust their receiving antenna's polarization direction and mode to match the satellite's for successful polarization matching. This ensures ground stations can capture sufficiently strong satellite signals to provide high-quality communication, supporting services like live satellite TV broadcasts, satellite telephony, and satellite data transmission.
The mobile communication sector also serves as a crucial application scenario for polarization matching technology. As smartphones proliferate and mobile internet rapidly evolves, users demand increasingly higher standards for communication quality and speed. Urban environments, populated by towering buildings, present complex signal propagation settings where polarization matching technology plays a vital role in enhancing signal reception quality and stabilizing communication. The polarization matching between mobile phones and base station antennas directly affects user experience. As phones change position and orientation relative to base stations during mobility, continuity and stability depend on the phone antenna's ability to adaptively adjust polarization to match the base station's. High-end smartphones employ smart antenna technology, featuring multiple built-in antenna units and advanced signal processing algorithms, automatically adjusting antenna polarization modes and directions to achieve optimal base station matching, enhancing signal reception strength, minimizing signal fading, and interference, and delivering smooth calls and high-speed data services to users.
In radar systems, polarization matching technology is indispensable. Radar relies on emitting electromagnetic waves and receiving target-reflected echoes to detect target positions, velocities, and shapes. Since targets exhibit different scattering properties toward electromagnetic waves, their echo polarization characteristics vary. Through leveraging polarization matching, radar can enhance target echo signals, suppress interference, and improve detection capabilities and recognition accuracy by designing appropriate polarization emission and reception methods based on target polarization characteristics. Militarily, polarization matching technology assists in target identification and classification, enabling radar to discern different target types—such as aircraft, missiles, and ships—and even recognize specific models and features, providing critical intelligence support for military operations. In meteorological radar applications, polarization matching helps detect precipitation particle shapes, sizes, and states, assisting meteorologists in more accurately predicting weather changes.
Looking ahead, polarization matching technology holds promising prospects in communication fields, particularly within emerging technologies like 5G and 6G, where it will assume an increasingly critical role, guiding communication advancements to higher stages.
