Millimeter waves are electromagnetic waves with wavelengths ranging from 10 mm to 1 mm and frequencies between 30 GHz and 300 GHz. Communication using these waves is known as millimeter wave communication, which can be divided into two main types: millimeter wave waveguide communication and millimeter wave radio communication. The millimeter wave band typically refers to the frequency range of 30 GHz to 300 GHz, corresponding to wavelengths of 1 mm to 10 mm. This type of communication uses millimeter waves as a carrier for transmitting information, and much of the current research focuses on specific "atmospheric window" frequencies and "attenuation peak" frequencies.
Millimeter wave communication has several unique propagation characteristics. First, it is a typical line-of-sight transmission. Since millimeter waves operate in a very high frequency band, they propagate as direct waves with narrow beams and strong directivity. However, due to atmospheric absorption and rain fade, the single-hop communication distance is limited. On the other hand, because of the high frequency and low interference, the propagation is stable and reliable. This makes millimeter wave communication ideal for high-quality, consistent wireless communication channels.
Second, millimeter waves exhibit both "atmospheric windows" and "attenuation peaks." The atmospheric windows occur at frequencies such as 35 GHz, 45 GHz, 94 GHz, 140 GHz, and 220 GHz, where signal attenuation is minimal. These bands are well-suited for point-to-point communication and are used in systems like low-altitude air-to-ground missiles and ground-based radars. In contrast, "attenuation peaks" appear around 60 GHz, 120 GHz, and 180 GHz, where signal loss can reach up to 15 dB/km or more. These frequencies are often used in secure, multi-channel networks to enhance network safety.
Third, millimeter waves experience significant attenuation during rainfall. Compared to microwaves, millimeter waves are more vulnerable to weather conditions, especially heavy rain, which can severely impact signal propagation. Studies show that the extent of this attenuation depends on factors like rainfall intensity, distance, and raindrop size. To mitigate this, sufficient signal margin must be built into the system design.
Fourth, millimeter waves have strong penetration through dust and smoke. Unlike infrared or laser signals, which are easily scattered by particles in the air, millimeter waves can pass through sand and smoke with minimal loss. Even under extreme conditions like explosions or metal foil strips, the fading caused is usually temporary and recovery is quick. This makes millimeter waves particularly useful in environments where visibility is poor.
In terms of research status, current millimeter wave communication systems include terrestrial point-to-point communication and satellite-based systems. Terrestrial systems are widely used in applications requiring high privacy, such as relay communications. Their strong concealment and resistance to interference make them ideal for secure transmissions. Additionally, the use of small antennas and narrow beams helps prevent interception and eavesdropping.
Satellite communication using millimeter waves has also seen rapid development due to the availability of frequency resources. For example, interstellar communication often uses the 60 GHz band, where atmospheric loss is so high that ground-based detection is nearly impossible. This ensures secure and reliable long-distance communication. The advantages of satellite communication include long-distance capability, broadcast mode support, large capacity, and self-sufficiency in monitoring and receiving.
In military applications, millimeter waves play a crucial role in electronic countermeasures, radar, guidance, and remote sensing. They are especially valuable in modern warfare, where intense electronic battles require communication systems with strong anti-jamming capabilities. By operating in the "attenuation peak" bands, such as 60 GHz, 120 GHz, and 200 GHz, millimeter wave systems can significantly reduce the risk of interception and interference.
Looking ahead, millimeter wave communication is expected to expand into various civilian applications, including broadband multimedia systems, vehicle collision avoidance, topographic mapping, and satellite links. Its potential for high data rates, secure transmission, and all-weather operation makes it a promising technology for future wireless communication. As research continues to advance, the use of millimeter waves will likely become even more widespread, transforming both military and commercial communication landscapes.
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