Propagation Path


Radio wave can be propagated from the transmitting antenna to the receiving
antenna in many ways: perpendicular incidence wave or ground refraction
wave, diffraction wave, troposphere reflection wave, ionosphere reflection
wave, as shown in the diagram. As for radio wave, the most simple
propagation mode between the transmitter and the receiver is free space
propagation. One is perpendicular incidence wave; the other is ground
reflection wave. The result of overlaying the perpendicular incidence wave
and the reflection wave may strengthen the signal, or weaken the signal,
which is known as multi-path effect. Diffraction wave is the main radio wave
signal source for shadow areas such building interior. The strength of the
diffraction wave is much dependent of the propagation environment. The
higher the frequency is, the weaker the diffraction signal will be. The
troposphere reflection wave derives from the troposphere. The heterogeneous
media in the troposphere changes from time to time for weather reasons. Its
reflectance decreases with the increase of height. This slowly changing
reflectance causes the radio wave to curve. The troposphere mode is
applicable to the wireless communication where the wavelength is less than
10m (i.e., frequency is greater than 30MHz).Ionosphere reflection propagation:
When the wavelength of the radio wave is less than 1m (frequency is greater
than 300MHz), the ionosphere is the reflector. There may be one or multiple
hops in the radio wave reflected from the ionosphere, so this propagation is
applicable to long-distance communication. Like the troposphere, the
ionosphere also presents the continuous fluctuation feature.
In a typical cellular mobile communication environment, a mobile station is
always far shorter than a BTS. The direct path between the transmitter and the
receiver is blocked by buildings or other objects. Therefore, the
communication between the cellular BTS and the mobile station is performed
via many other paths than the direct path. In the UHF band, the
electromagnetic wave from the transmitter to the receiver is primarily
propagated by means of scattering, namely, the electromagnetic wave is
reflected from the building plane or refracted from the man-made or natural