Online calculator and formulas for calculating the resistances of a Pi attenuator
In the case of attenuators for high frequencies, attention must be paid to the impedance matching. The input impedance and the output impedance must be equal to the wave impedance of the lines.
On this side, a pi attenuator is calculated whose resistances, i.e. also the impedance, are the same on the input and output sides.
If the resistances on the input and output sides are not the same, an impedance matching takes place at the same time as the attenuation.

The resistances R1 and R2 of the PI attenuator are calculated from the impedance Z and the attenuation factor a. The damping factor a is calculated from the ratio of the output voltage to the input voltage (U_{1} / U_{2}), or the attenuation measure ΔL in db.
\(\displaystyle a=\frac{U_1}{U_2}= 10^{\frac{ΔL}{20 db}}\)
\(\displaystyle R_1= Z\frac{a^21}{2a}\)
\(\displaystyle R_2= Z\frac{a+1}{a1}\)
