Z_in desired input impedance in Ω

Z_out desired output impedance in Ω

a attenuation in dB

L = 10^a/10 (the loss)

A = (L + 1)/(L − 1)

Pi attenuator

R2 = (L − 1)/2 * √ ((Z_in * Z_out)/L)

R1 = 1/( A/Z_in − 1/R2)

R3 = 1/ (A/Z_out − 1/R2)