What blocks millimeter waves?

Millimeter waves propagate solely by line-of-sight paths. They are not reflected by the ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do. At typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage.

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Why Millimetre waves are used in 5G?

Comparatively, the maximum carrier frequency of the 4G-LTE band, 2 GHz, provides an available spectrum bandwidth of only 100 MHz. Therefore, using millimeter wave frequencies can easily increase the spectrum bandwidth by a factor of 10, allowing for a massive increase in transmission speeds .

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