It is generally considered that the millimeter wave frequency range is 26.5～300GHz, and the bandwidth is as high as 273.5GHz, which is more than 10 times the full bandwidth from DC to microwave. Even if atmospheric absorption is considered, only four main windows can be used when propagating in the atmosphere, but the total bandwidth of these four windows can reach 135 GHz, which is 5 times the sum of the bandwidth of each band below the microwave. This is undoubtedly very attractive today when frequency resources are tight. The beam of millimeter wave is much narrower than that of microwave under the same antenna size. Therefore, it is possible to distinguish small targets closer together or observe the details of the target more clearly.
Broadband and broad-spectrum capabilities can be used to suppress multipath effects and clutter echoes. There are a large number of frequencies available to effectively eliminate mutual interference. A larger Doppler frequency shift can be obtained at the target radial velocity, thereby improving the detection and identification capabilities of low-speed moving objects or vibrating objects.
This advantages of millimeter wave communication come from two aspects: (1) Because mmWaves propagate in the atmosphere and are greatly attenuated by the absorption of oxygen, moisture and rainfall, the point-to-point through distance is very short, and the signal will become very weak beyond this distance. And this increases the difficulty of eavesdropping and interference by the enemy. (2) The beam of millimeter wave is very narrow and the sidelobe is low, which further reduces the probability of being intercepted. With more and more fields finding out millimeter wave advantages, the application of millimeter wave will spread the whole world and even change the world.
Because there are basically no interference sources in high-frequency millimeter wave communications, and the electromagnetic spectrum is extremely clean, the millimeter wave channel is very stable and reliable, and its bit error rate can be maintained at the order of 10-12 for a long time, which is comparable to the transmission quality of optical cables.
The penetration ability of millimeter waves to rainfall, dust, smoke and plasma is much stronger than that of atmospheric lasers and infrared. This enables millimeter wave communications to have better all-weather communications capabilities, ensuring continuous and reliable work. Compared with microwaves, millimeter wave components are much smaller in size. Therefore, the millimeter wave system is easier to miniaturize.
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