Page 149 - Satellite Communications, Fourth Edition

Polarization 129

E 1

E 11
Depolarizing
medium

E 12

(a)

E 1

E 11
Depolarizing
medium
E 21

E 12
E 2 E 22
(b)
Figure 5.11 Vectors defining (a) cross-polarization discrimination
(XPD), and (b) polarization isolation (I).

The second situation is shown in Fig. 5.11b. Here, two orthogonally
polarized signals, with magnitudes E and E , are transmitted. After
2
1
traversing the depolarizing medium, copolar and cross-polar components
exist for both waves. The polarization isolation is defined by the ratio of
received copolar power to received cross-polar power and thus takes into
account any additional depolarization introduced by the receiving system
(Ippolito, 1986). Since received power is proportional to the square of the
electric field strength, the polarization isolation in decibels is defined as

E 11
I 20 log (5.18)
E 21