How does the addition of a bias-t circuit affect the impedance of a transmission line?
The capacitor and inductor values are chosen so as not to disturb the line impedance. In practice, we would aim for the capacitor in this case to be as near a short circuit (0 Ohm impedance) and the inductor as near an open circuit (infinite impedance) at the frequency of interest (~1575MHz or 1227MHz for GPS). Just use RF components (I would recommend a low ESR chip-scale ceramic cap and chip-scale wound inductor) and as a rule of thumb I'd be looking for a cap impedance &lt;1 Ohm and inductor impedance >20x your line impedance.