The gain of a parabolic reflector can be defined using the equation
where
with the beamwidth of the antenna being
where
So with some basic math, the gain of the 6ft dish at GPS frequencies 1575.42 MHz,
times mag
times mag
To convert that into dB isotropic,
dBi gain
dBi gain
with a beamwidth of
So with some basic math, the gain of the 6ft dish at GPS frequencies 10.455 GHz,
times mag
times mag
dBi gain
dBi gain
with a beamwidth of