Usually the millimeter wave frequency band refers to 30GHz to 300GHz, and the corresponding wavelength is 1mm to 10mm. Millimeter wave communication refers to the communication carried out by using millimeter wave as the carrier of transmitting information. At present, the vast majority of applied research focuses on several "atmospheric window" frequencies and three "attenuation peak" frequencies.
The millimeter wave belongs to the very high frequency band. It propagates in space as a direct wave. The beam is very narrow and has good directivity. On the one hand, because the millimeter wave 5G is seriously affected by atmospheric absorption and rainfall fading, the single-hop communication distance is short; on the other hand, due to the high frequency band and few interference sources, the propagation is stable and reliable. Therefore, millimeter wave communication is a typical communication technology with high-quality, constant-parameter wireless transmission channels.
The "atmospheric window" refers to the 35GHz, 45GHz, 94GHz, 140GHz, and 220GHz frequency bands. The millimeter wave propagation near these special frequency bands suffers less attenuation. Generally speaking, the "atmospheric window" frequency band is more suitable for point-to-point communications, and has been adopted by low-altitude air-to-surface missiles and ground-based radars. The attenuation near the 60GHz, 120GHz, and 180GHz frequency bands has a maximum value of about 15dB/km or more, which is called the "attenuation peak". Usually these "attenuation peak" frequency bands are preferentially selected by hidden networks and systems with multi-channel diversity to meet the requirements of network safety factors.
Atmospheric lasers and infrared have poor penetration of dust and smoke, while millimeter waves have obvious advantages in this regard. A large number of field test results show that millimeter waves have strong penetrating power to dust and smoke, and can pass through dust and smoke almost without attenuation. Even under the conditions of higher intensity scattering produced by explosions and metal chaffs, even fading is short-term and will soon recover. With the diffusion and landing of ions, it will not cause serious interruption of millimeter wave communication.