Pi Attenuator Calculator

Design a symmetrical π (Pi) attenuator for impedance matching and signal level reduction. This network uses three resistors to provide a specific attenuation while maintaining a constant system impedance.

Schematic

Component Values

R1, R3 (shunt):
R2 (series):

Calculated Performance

Actual Attenuation:
Input Impedance:
Return Loss:
VSWR:

Design Equations

For a symmetrical Pi attenuator with attenuation $A$ (in dB) and characteristic impedance $Z_0$:

Voltage ratio: $K = 10^{A/20}$
Shunt resistors: $R_1 = R_3 = Z_0 \cdot \frac{K + 1}{K - 1}$
Series resistor: $R_2 = Z_0 \cdot \frac{K^2 - 1}{2K}$

Design Notes

Standard E24 resistor values are used for "Actual" results.
For high power applications, ensure resistors can handle the dissipated power.
At high frequencies (RF), parasitic capacitance and inductance of resistors become significant.
Symmetrical design means Input and Output impedance are intended to be identical.