Multi-dimensional Difference Analysis and Application Guide of Linear Polarization and Circular Polarization Antennas

　　Multi-dimensional Difference Analysis and Application Guide of Linear Polarization and Circular Polarization Antennas

　　In the field of wireless communications, customers are often confused about the characteristics of linear polarization and circular polarization antennas. In fact, these two antennas are based on different electromagnetic wave polarization methods, and show significant differences in signal propagation mechanism, system adaptability and engineering application. In-depth analysis of their characteristics is of great significance to optimizing the design of wireless communication systems and improving signal transmission quality.

　　I. Essential Differences in Polarization Methods

　　(I) Linear Polarization: Linear Vibration of the Electric Field Vector

　　During the propagation process, the electromagnetic wave electric field vector of the linear polarization antenna always vibrates along a fixed straight line direction, which can be divided into three types: horizontal polarization, vertical polarization and tilted polarization. Taking the Wi-Fi routers used in daily life as an example, many devices use horizontal polarization, and the electric field vector propagates parallel to the ground. This design facilitates effective coverage in indoor environments; while FM broadcast systems mostly use vertically polarized antennas, whose electric field vectors are perpendicular to the ground, which can effectively penetrate obstacles such as buildings in urban environments and achieve stable signal transmission. For tilted polarized antennas, such as when the electric field vector is at a 45° angle to the horizontal or vertical direction, in some special communication scenarios, the signal reception effect is optimized by adjusting the polarization angle.

　　(II) Circular polarization: Rotational trajectory of the electric field vector

　　When propagating, the electric field vector of the electromagnetic wave of the circularly polarized antenna rotates around the propagation direction at a constant rate, forming a circular trajectory on a plane perpendicular to the propagation direction, which is divided into right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP). In the Global Positioning System (GPS), the signal transmitted by the satellite adopts right-hand circular polarization, and the ground receiving equipment can stably receive the signal through the matching right-hand circular polarization antenna; in some satellite communication systems, the left-hand circular polarization antenna also plays an important role to ensure the reliable transmission of the signal.

　　II. Comparison of antenna direction and attitude sensitivity

　　(I) Linear polarization antenna: strict direction matching requirements

　　Linear polarization antennas are extremely sensitive to the relative direction of the transmitting and receiving antennas. When the polarization directions of the transmitting and receiving antennas are consistent, the signal can be transmitted efficiently and the reception effect is optimal; if the polarization directions are orthogonal, such as the transmitting antenna is vertically polarized and the receiving antenna is horizontally polarized, according to electromagnetic theory, the signal will be greatly attenuated. Theoretically, the polarization isolation between the two is almost infinite, and in practical applications, the isolation can reach more than 30dB, making the signal almost impossible to receive. This feature makes linearly polarized antennas suitable for fixed installation scenarios, such as point-to-point communication between base stations, and in multiple-input multiple-output (MIMO) systems, polarization diversity is achieved using orthogonally polarized antennas, effectively improving communication capacity.

　　(II) Circularly polarized antennas: flexible attitude adaptability

　　Circularly polarized antennas are insensitive to the relative rotation of the transmitting and receiving antennas. As long as the transmitting and receiving antennas are both right-hand circularly polarized or left-hand circularly polarized, the signal strength remains basically stable even if the antennas rotate during use. When the transmitting and receiving antennas rotate in opposite directions, the signal will be completely isolated, and the polarization isolation is usually greater than 20dB. This characteristic gives circularly polarized antennas unique advantages in mobile devices and platforms with unstable postures, such as drone communications, satellite navigation systems, and high-speed motion scenes such as rockets and spacecraft. They can effectively cope with the impact of changes in device posture and ensure the stability of signal transmission.

　　III. Significant difference in anti-multipath interference capabilities

　　(I) Linearly polarized antennas: the trouble of multipath interference

　　In complex urban environments, linearly polarized antennas are extremely susceptible to multipath interference. Due to the reflection of electromagnetic waves by obstacles such as buildings and walls, the polarization direction of the reflected signal may change. When the reflected signal is superimposed on the direct signal, it will cause fluctuations in signal strength and even signal cancellation, which seriously affects the communication quality. For example, in urban areas with high-rise buildings, when wireless communication equipment uses linearly polarized antennas, signal fading is more obvious, resulting in problems such as reduced data transmission rate and unstable connection.

　　(II) Circularly polarized antennas: natural anti-interference advantages

　　Circularly polarized antennas have natural anti-multipath interference capabilities. When a circularly polarized wave encounters a smooth surface and is reflected, its rotation direction will reverse, such as a right-hand circularly polarized wave that is reflected and becomes a left-hand circularly polarized wave. The receiving antenna (such as a right-hand circularly polarized antenna) will naturally suppress the reflected wave (left-hand circularly polarized wave) and significantly reduce multipath fading through the polarization isolation mechanism. Taking the GPS navigation system as an example, the circularly polarized antenna can effectively avoid the positioning drift problem caused by the reflected signal from the building and ensure the accuracy of the positioning accuracy.

　　IV. Implementation method and structural characteristics

　　(I) Linear polarization antenna: simple and efficient structural design

　　The structure of linear polarization antenna is relatively simple. Common types include dipole antenna, microstrip patch antenna (single feed point) and Yagi antenna. The dipole antenna consists of two symmetrical conductors, with a simple structure and easy to make. It is widely used in various wireless communication devices; the single-feed point microstrip patch antenna is excited by a single feed point and has the advantages of small size and light weight. It is widely used in small electronic products such as mobile phones and Bluetooth devices.

　　(II) Circularly polarized antenna: complex and sophisticated construction technology

　　The design of circularly polarized antennas needs to ensure that the amplitude of the electric field vector is equal and the phase difference is 90°. Common structural forms include single-feed point microstrip patches (circular polarization is achieved through angle cutting or slotting perturbation), dual-feed point microstrip patches (circular polarization is generated by using a 90° feeding phase difference), helical antennas (axial mode working mode) and cross dipoles (circular polarization is formed by feeding with a 90° phase difference). These structural designs are relatively complex, but they can meet the needs of circularly polarized signals in different application scenarios. For example, helical antennas are often used in the field of satellite communications and can achieve broadband circular polarization characteristics to meet the special requirements of satellite signal reception.

　　V. Analysis of differences in bandwidth characteristics

　　(I) Linearly polarized antenna: wider bandwidth advantage

　　Linearly polarized antennas usually have wider bandwidths. Taking dipole antennas as an example, their bandwidth can reach more than 10%, which can achieve stable signal transmission over a wider frequency range. This broadband characteristic makes linear polarization antennas suitable for communication systems with high frequency adaptability requirements, such as radio and television signal transmission, broadband wireless access and other fields.

　　(II) Circularly polarized antennas: limited bandwidth and special breakthroughs

　　Since circularly polarized antennas need to strictly meet the conditions of equal amplitude and orthogonal phase, their bandwidth is usually narrow, and the typical 3dB axial ratio bandwidth is only 1% - 5%. However, the helical antenna is an exception. It can achieve broadband circular polarization characteristics and is widely used in fields such as satellite communications. In actual design, engineers strive to broaden the bandwidth of circularly polarized antennas by continuously improving antenna structures and optimizing design parameters to meet the needs of more application scenarios.

　　In the design of wireless communication systems, the choice of linear polarization or circular polarization antennas needs to comprehensively consider the needs of actual application scenarios. If the relative positions of the transmitting and receiving antennas are fixed and the communication environment has less reflection, such as point-to-point microwave links, linearly polarized antennas become the first choice due to their high efficiency and simple structure; in complex environments where the terminal posture changes frequently or there are strong reflections, such as indoor positioning, drone image transmission and other scenarios, the anti-rotation and anti-multipath interference advantages of circularly polarized antennas are indispensable. In addition, with the continuous development of communication technology, more complex polarization forms such as elliptical polarization are gradually applied to practical systems, but linear polarization and circular polarization, as the most basic and widely used polarization forms, have always been the focus of research and application in the field of wireless communication. A deep understanding of their differences will provide strong support for the optimal design of wireless communication systems.