The reliability of the system generally can be improved by the use of a second receiving antenna located at a different height (“space diversity”). Both antennas (primary and diversity) feed the receiver through appropriate switching devices.

The space diversity improvement factor for vertically separated receive antennas is computed as:

I = (7 x 10-5 x f x s2 x 10F2/10 ) / D

where:

• I is the space diversity improvement factor
• f is the frequency in GHz.
• s is the vertical antenna spacing in feet.
• D is the path length in miles.
• F2 is the lower fade margin in dB.

In space diversity systems, fade margins are computed for both antennas. The larger fade margin value is used to compute the non-diversity reliability, and the smaller fade margin value is used to compute the space diversity improvement.

The overall reliability with space diversity is computed by dividing the non-diversity outage probability by the improvement factor:

Udiv = Undb/I