Propagation Properties of Metric, Decimeter and Centimeter Waves
Meter wave (frequency 30MHz-300MHz), decimeter wave (frequency 300MHz-3GHz) and centimeter wave (frequency 3GHz-30GHz) are usually called ultrashort waves or microwaves. They are rapidly attenuated by the absorption of the earth during the propagation process, the diffraction ability is very poor, and they cannot be reflected back when they encounter the ionosphere. Therefore, electromagnetic waves in these frequency bands are usually only used for line-of-sight propagation and scattering propagation.
Line-of-sight propagation, as the name implies, is to propagate within the "visible" distance, that is, there is no obstruction between the transmitting antenna and the receiving antenna. Mainly used in radio and television, mobile communication, microwave relay, wireless access, radar and other systems. The "line-of-sight" can sometimes be extremely distant, such as the space communication between the earth and deep space probes, and the reception of electromagnetic radiation signals from celestial bodies by radio astronomy observatories.
Scattering propagation is mainly concentrated in the 30MHz-100MHz and 700MHz-10000MHz frequency bands. When electromagnetic waves encounter unevenly distributed objects (charged media) in the troposphere and ionosphere, a portion of the electromagnetic waves will be scattered back to the ground. Therefore, scattering propagation can be used for over-the-horizon communication. Compared with the sky wave communication in the short-wave band, it is not affected by nuclear explosions, sunspots, magnetic storms and aurora.
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