A17.5.3 Attenuation due to diffraction

According to ITU-R Rec. P.526-2, the diffraction loss  L_p (d) can be derived by the received field strength  E referred to the free space E₀ :

                                              (Eq. 211)

with:

  X     is the normalized radio path between transmitter and receiver 

   Y1     is the normalized antenna height of the transmitter 

    Y2    is the normalized antenna height of the receiver

where:

 is a parameter derived from the earth admittance factor K  : =1 for > 20 MHz.

 f is the frequency in MHz

a_e is the equivalent earth radius in km (definition see below)

d is the distance in km

h_i is the antenna height above ground in m with =1 or 2 for the transmitter or receiver, respectively

The distance-dependent term F(X)  is given by the semi-empirical formula:

                                             (Eq. 212)

The antenna height gain G(Y) is given by the formula set:

                              for Y>2                                                (Eq. 213)

 for  10K < Y < 2                                 

                  for    K/10 < Y < 10K                      

                                                              for    Y < K/10                                 

where K is the normalized earth surface admittance factor (see ITU-R Rec. P.526), default value 10e-5:

All frequencies used attenuation due to diffraction have the unit MHz in contrast to the attenuation due to atmosphere where GHz is applied.