Antenna Theory - Terms in Wave Propagation
In the process of propagation of a wave, there are few terms which we come across quite often. Let us discuss about these terms one by one. Virtual Height When a wave is refracted, it is bent down gradually, but not sharply. However, the path of incident wave and reflected wave are same if it is reflected from a surface located at a greater height of this layer. Such a greater height is termed as virtual height. The figure clearly distinguishes the virtual height (height of wave, supposed to be reflected) and actual height (the refracted height). If the virtual height is known, the angle of incidence can be found. Critical Frequency Critical frequency for a layer determines the highest frequency that will be returned down to the earth by that layer, after having been beamed by the transmitter, straight up into the sky. The rate of ionization density, when changed conveninetly through the layers, the wave will be bent downwards. The maximum frequency that g...