Ground Defenses
If your base has Deflection Shields, they will add shielding to all ground-battery defenses (from barracks to disruptors)
The math behind it is:
total of shields divided by total of area
shields = deflection shielding * 5
area = sum of all battery levels * 5
limited to a maximum increase of 3 shielding per battery.
For a simple example, if a base has 1 barracks, 1 laser battery, 2 ion battery and 1 deflection shields, then:
(1+1+2)*5=20 area
1 deflection=20 shielding (add 5% to each shielding tech level you have)
so each ground defense would get 1 extra shielding.
Base Owner Orbiting Ships
To the orbiting ships the bonus is similar, divide the total number of units you have by the p.shields or s.shields
1000 ft
1 level of p.shields
24*5 / 1000 = 0.12
if you have shielding tech 20, it would give double that shielding to your fighters.
Shielded units will have their shielding increased.