Hertziani Connections
Ideal propagation in the free space
1) Solution of the equations of Maxwell to great distance from the antenna:
it is observed that superficial the equiphase ones are of the spheres centered on the source and that and and H is orthogonal between they and to the propagation direction.
2) Parameters of an antenna :
An imaginary isotropic radiator irradiates power in all
the directions, at a distance r from it the power density is 
, a real antenna comes confronted to it by means of the
function of gain 
the whose maximum value is
called gain of G antenna, a lot used in the application is also EIRP =
PG.
For a receiving antenna the received power is function of
the density of 
power that acts on it and of the
area equivalent Toand , is had
that is 
. And it is characterized from a
reception gain 
.
3) Attenuation of transmission in the free space :
it therefore increases with the square of the frequency, but being in kind the band the much smallest one of the carrying frequency, pu² to suppose that the transmission attenuation is almost constant in band.
Propagation in the real space
4) eiconale Equation and its implications :
it is a lot important in how much from it derives the
relation that it concurs to determine the trajectory of the beams 
in particular is had that in the troposphere
(h < 20Km) n second depends on the quota the 
relation where p is the pressure total while pto it is the partial pressure of the
vapor of water, to varying of these factors distinguishes the 3
following situations:
to) atmosphere standard n it diminishes to growing of h therefore the curving is turned towards the land surface
b) atmosphere super-standard n diminishes still more in emphasized way to growing of h
to) atmosphere sub-standard n it increases to growing of h and therefore the concavity is turned towards the high
5) Effects of the ionosphere :
It is a zone that is found to approximately 80Km from the land surface and is characterized from elevated free electron concentrations that are behaved as a conductive sheet in a position to absorbing and rifrangere frequencies comprised between 5MHz and 30MHz concurring connections beyond the optical capacity.
6) ground Wave :
The earth has a good conductivity therefore the
electromagnetic field propaga also along its surface, however to the
attenuation from free space a term joins 
with p
employee from the square of the frequency, that means that such
propagation only has importance for inferior frequencies to 10MHz.
7) Diffraction :
It is the phenomenon for which us it can be communication also between 2 antennas between which an obstacle is interposed, it is explained by means of the principle of Huygens-Fresnel according to which every point in which the cancellation reaches becomes source of secondary spherical waves.
8) Attenuation due to the rain :
it is worth approximately 1dB/Km in intense rain conditions to 10GHz and can arrive until to 8dB/Km in the same conditions to 30GHz.
9) Characterization statistics of the hertziani connections :
The causes that can determine of the weakenings of mark them are following:
Weakenings in the long term
Variations of the refractive index can give place to variations of the curving beam, as also the presence of a zone to refractive index much bottom can reflect marks them, the total effect from place to one lognormale statistics.
Weakenings in the short term
The presence in the troposphere of various layers with gradient of refractive indices can give place to way multiple.
