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Pi Attenuator Calculator

A 10 dB pi attenuator for 50 Ω uses R1 = 96.25 Ω (shunt) and R2 = 71.15 Ω (series).

By Jasper · Updated

Calculator

PASS10.00 dBE96 10.05 dB

K = 10^(A/20). Matched both ports to Z0. E96 nearest preferred values are re-driven with 20·log10(|Vin/Vout|). A above 60 dB: parasitics dominate; values are theoretical.

Z0 presets:

K
3.162
R shunt
96.25 Ω
R series
71.15 Ω
Zin
50 Ω
Ideal att
10.00 dB
R shunt E96
95.3 Ω
R series E96
71.5 Ω
E96 Zin
49.8 Ω
E96 att
10.05 dB
Return loss
∞
E96 return loss
53.84 dB
  • Pass K: K = 10^(A/20) = 3.16228
  • Pass Input impedance: Zin = 50.0000 Ω

Formula

Voltage ratio

K=10A/20 K = 10^(A/20)

High attenuation

A>60dB A above 60 dB: parasitics dominate; values are theoretical

Preferred values

RE96=nearestE96(R) E96 nearest preferred values

Pi Attenuator Calculator

Rsh=Z0K+1K-1,Rse=Z0K2-12K Rsh = Z0 (K+1)/(K−1); Rse = Z0 (K²−1)/(2K)

Variables

Symbol Meaning Unit Typical range Precision Default
A Attenuation dB ≥ 0 dB A must be > 0 4 sig 10 dB
Z0 Characteristic impedance Ω ≥ 0 mΩ 4 sig 50 Ω
Pin Input power (optional) W ≥ 0 µW 4 sig
K Voltage ratio — — 4 sig —
Zin Input impedance Ω — 4 sig —
AdB Ideal attenuation dB — 4 sig —
AE96 E96 attenuation dB — 4 sig —
RL Return loss dB — 4 sig —
Rsh Shunt resistor Ω — 4 sig —
Rse Series resistor Ω — 4 sig —
RshE96 Shunt E96 Ω — 4 sig —
RseE96 Series E96 Ω — 4 sig —
PshIn Input shunt dissipation W — 4 sig —
Pse Series dissipation W — 4 sig —
PshOut Output shunt dissipation W — 4 sig —
Pload Load power W — 4 sig —

Worked example

10 dB / 50 Ω

Input Value
A · Attenuation 10 dB
Z0 · Characteristic impedance 50 Ω
Output Value
K · Voltage ratio 3.162
AdB · Ideal attenuation 10 dB
AE96 · E96 attenuation 10.05 dB
Zin · Input impedance 50 Ω
Rsh · Shunt resistor 96.25 Ω
Rse · Series resistor 71.15 Ω

6 dB / 50 Ω

Input Value
A · Attenuation 6 dB
Z0 · Characteristic impedance 50 Ω
Output Value
AdB · Ideal attenuation 6 dB
K · Voltage ratio 1.995

How it works

A π-pad is two shunts and one series resistor, matched to Z0 both ways. This page prints the ideal pair, the nearest E96 pair, and the voltage attenuation of that E96 network. Use the 50 / 75 / 600 Ω chips for the usual lines.

Pitfalls

  • Trusting A above 60 dB on a lumped pad. Parasitics dominate; the numbers are theoretical.
  • Driving an unmatched load and expecting Zin = Z0.
  • Snapping only one resistor to E96.

FAQ

What resistors make a 10 dB, 50 Ω π-pad?

About 96.2 Ω shunt and 71.2 Ω series. E96 is 95.3 Ω and 71.5 Ω.

Why does A = 0 fail?

K = 1 and the formulas divide by K−1.

What does A above 60 dB mean here?

The algebra still runs, with a warning that parasitics dominate and the values are theoretical.

Is the E96 attenuation 10 log or 20 log?

20·log10(|Vin/Vout|) of the loaded pad.

Related

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