Analysis of the core difference between left-handed and right-handed image transmission antennas

　　Analysis of the core difference between left-handed and right-handed image transmission antennas

　　In the field of wireless image transmission, the left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) of image transmission antennas play an important role in various communication scenarios due to their unique electromagnetic wave polarization characteristics. The core difference between the two polarization modes stems from the different rotation directions of the electric field vectors of electromagnetic waves, and this essential difference is further extended, which has a profound impact on signal transmission efficiency, anti-interference ability, gain characteristics and actual application scenarios. Next, we will conduct an in-depth analysis of the difference between left-handed and right-handed image transmission antennas from multiple dimensions such as technical principles, performance comparison, and practical applications.

　　1. Basic principles: the essential difference in the direction of rotation of the electric field vector

　　(I) Physical definition of rotation direction

　　From the perspective of the direction of electromagnetic wave propagation, the electric field vector of the electromagnetic wave radiated by the left-hand circular polarization (LHCP) antenna rotates in the counterclockwise direction; while the electric field vector of the right-hand circular polarization (RHCP) antenna rotates in the clockwise direction. This difference in rotation direction is the fundamental mark to distinguish the two polarization modes.

　　(II) Orthogonal characteristics of rotation

　　LHCP and RHCP are orthogonal to each other, that is, a left-hand circularly polarized antenna can hardly effectively receive a right-hand circularly polarized signal, and vice versa. This "rotational isolation" feature is of great significance in practical applications. Its isolation can reach up to 78dB, which can significantly reduce the crosstalk between signals of different rotations and provide a guarantee for the pure transmission of signals. For example, in a complex multi-antenna communication environment, this feature can effectively avoid signal interference between different antennas and improve the stability of the communication system.

　　(III) The key role of polarization matching

　　In a wireless image transmission system, the transmitter and the receiver must use circularly polarized antennas with the same rotation direction to achieve efficient signal transmission. Once polarization mismatch occurs, that is, the rotation directions of the transmitter and the receiver antennas are inconsistent, it will cause serious signal loss. This loss will not only reduce the clarity and smoothness of image transmission, but may also cause transmission interruption, affecting the normal operation of the entire communication system.

　　2. Performance Difference: Comparison of Advantages and Disadvantages in Multiple Dimensions

　　(I) Signal Transmission Efficiency

　　Matching Scenario: When the transmitting antenna and the receiving antenna have the same rotation direction, the signal can be transmitted efficiently and the receiving efficiency can be maximized. For example, in a system using an LHCP transmitting antenna with an LHCP receiving antenna, the signal strength can be fully guaranteed, and the quality and stability of image transmission are also improved.

　　Mismatching Scenario: Once the transmission and receiving antenna rotation directions do not match, such as LHCP transmission with RHCP reception, the signal will be severely attenuated, with an attenuation of more than 20dB. This large signal attenuation will cause problems such as blurring, freezing, and even loss of the image, greatly affecting the image transmission effect.

　　Comparison with linear polarization: When a linear polarization antenna receives a circularly polarized signal, there is an inherent loss of about 3dB, which means that a linear polarization antenna can only receive half the power of a circularly polarized signal. In contrast, the signal transmission efficiency between circularly polarized antennas with the same rotation direction has obvious advantages.

　　(II) Anti-interference and multipath suppression capability

　　Reflection wave rotation reversal mechanism: When a circularly polarized wave encounters a plane or spherical reflection, its rotation will reverse, that is, the LHCP wave becomes an RHCP wave after reflection, and the RHCP wave becomes an LHCP wave after reflection. This feature makes the circularly polarized antenna perform well in suppressing multipath interference. For example, in a system consisting of an LHCP transmitting antenna and an LHCP receiving antenna, the RHCP signal generated by the reflection will be naturally suppressed by the receiving antenna, thereby effectively reducing the interference of multipath signals to the main signal.

　　Actual application case: In the ship-ground image transmission system, by using the LHCP receiving antenna, the isolation of the RHCP interference signal reaches 78dB, which significantly improves the clarity and stability of the image. In the mine UWB positioning system, the optimized RHCP antenna further enhances the ability to resist multipath interference by reducing the axial ratio (≤2dB) and increasing the cross-polarization level (>10dBi), ensuring the accuracy and reliability of the positioning data.

　　(III) Gain and Directivity

　　Gain difference: Although left-handed and right-handed antennas do not directly determine the gain of the antenna, the design and manufacturing process of the antenna will affect the performance of different rotation directions. In the measured data of satellite communications, in the 21.4GHz frequency band, the gain of the RHCP antenna is 36.3dBi, and the gain of the LHCP antenna is 36.7dBi, and the difference between the two is less than 0.5dBi. By optimizing the antenna design, such as reducing the axial ratio to < 3dB, the purity of a specific rotation direction can be further improved, thereby improving the gain performance of the antenna.

　　Coverage angle and application trade-off: For high-gain image transmission antennas, such as directional antennas, their coverage angle is usually narrow. In practical applications, it is necessary to weigh and choose between left-handed and right-handed antennas based on specific transmission distances and flexibility requirements. For example, in long-distance, point-to-point image transmission scenarios, you may prefer a high-gain directional antenna. At this time, you need to comprehensively consider the characteristics of left-handed and right-handed rotations and the coverage angle to ensure that the signal can be accurately transmitted to the target receiving end.

　　III. Application scenarios: selection strategies under different requirements

　　(I) Aerospace field

　　In aerospace image transmission, circularly polarized antennas are widely used due to the complex attitude changes of aircraft and the harsh signal transmission environment. According to the specific system design and anti-interference requirements, left-handed or right-handed circularly polarized antennas will be selected. For example, in order to avoid interference with other satellite signals, the image transmission link between some satellites and ground stations will use circularly polarized antennas with specific rotation directions according to satellite orbits and signal planning to ensure stable transmission of image data.

　　(II) UAV image transmission system

　　During the flight, the attitude of the drone is constantly changing and is easily interfered by the surrounding environment. Therefore, the drone image transmission system usually uses circularly polarized antennas to improve the stability and anti-interference ability of the signal. In some drone operations that need to cross complex terrain or buildings, selecting a circularly polarized antenna with a suitable rotation direction can effectively reduce multipath interference, ensure the real-time transmission of high-definition images, and provide operators with clear and accurate on-site images.

　　(III) Security monitoring field

　　In security monitoring systems, especially in complex outdoor environments, circularly polarized image transmission antennas are also used to ensure stable transmission of monitoring images. According to the layout of the monitoring area and the signal interference, the reasonable selection of left-handed or right-handed antennas can improve the signal coverage and transmission quality, and achieve effective monitoring of the monitoring area.

　　In summary, there are significant differences between left-handed and right-handed image transmission antennas in terms of basic principles, performance, and application scenarios. In the actual design and application of wireless image transmission systems, in-depth understanding of these differences and selection of antennas with appropriate rotation directions according to specific needs are the key to achieving efficient and stable image transmission. With the continuous development of communication technology, the research and application of left-handed and right-handed circularly polarized antennas will continue to deepen, bringing more innovations and breakthroughs to the field of wireless image transmission.