If we want receive signal level better than we need bigger dish. Usually for distance (d) :
d < 1 km the dish is 0.3m 1 km < d < 20 km the dish is 0.6m 20 km < d < 30 km the dish is 1.2 or 1.8 d > 30 the dish is 2.4m
But it is depend on planning
Space Diversity (SD): one hop (system) with two antennas at different height. By using to antennas, we can select one antenna which receive better and then the other at standby mode.
Frequency Diversity (FD) means one system using two frequency f1 and f2 then we select which receive better as ‘working frequency’ and the other as standby mode.
In SD and FD, the selection mode can be made automatically
that’s simple explanation, i hope help you