Page 152 - Satellite Communications, Fourth Edition

132 Chapter Five

Minor
axis

E V E' V

E'
E
c c
τ τ'

E' H
E H
Major
axis
Figure 5.13 Polarization vector relative to the major and minor axes of a raindrop.

shown that the depolarization resulting from the differential phase shift
is more significant than that resulting from differential attenuation.
The cross-polarization discrimination in decibels associated with rain
is given to a good approximation by the empirical relationship (CCIR
Report 564-2, 1982)
XPD U V log A (5.21)

where U and V are empirically determined coefficients and A is the rain
attenuation. U, V,and A must be in decibels in this equation. The
attenuation A is as determined in Sec. 4.4. The following formulas are
given in the CCIR reference for U and V for the frequency range 8 to
35 GHz:

20 for 8 f 15 GHz
V e (5.22a)
23 for 15 f 35 GHz

and

U 5 30 log f 10 log (0.5 0.4697 cos 4 ) 40 log(cos
) (5.22b)

where f is the frequency in gigahertz, q is the angle of elevation of the
propagation path at the earth station, and t is the tilt angle of the
polarization relative to the horizontal. For circular polarization t
45°. As shown earlier, for a satellite transmission, the angle ξ between
the reference plane containing the direction of propagation and the