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. 220)

with:

 

    is the normalized radio path between transmitter and receiver 

 

  is the normalized antenna height of the transmitter  

   is the normalized antenna height of the receiver

where:

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

 is the frequency in MHz

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

 is the distance in km

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

The distance-dependent term

  is given by the semi-empirical formula:

                       

 (Eq. 221)

The antenna height gain

 is given by the formula set:

(Eq. 222)   

    

 for  

 for  

       

  for    

                             

 for   

where

 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.