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Reflection Attenuator Calculator

A 10 dB reflection attenuator for 50 Ω uses Rhigh = 96.25 Ω and Rlow = 25.97 Ω.

By Jasper · Updated

Calculator

PASS10.00 dBE96 10.12 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. Requires a 90° hybrid coupler.

Z0 presets:

K
3.162
R high
96.25 Ω
R low
25.97 Ω
Zin
50 Ω
Ideal att
10.00 dB
R high E96
95.3 Ω
R low E96
26.1 Ω
E96 Zin
50 Ω
E96 att
10.12 dB
|Γ|
0.3162
Return loss
∞
E96 return loss
∞
  • 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

Reflection Attenuator Calculator

Rhi=Z0K+1K-1,Rlo=Z0K-1K+1 Rhi = Z0 (K+1)/(K−1); Rlo = Z0 (K−1)/(K+1)

Hybrid

Γ=K-1K+1 Requires a 90° hybrid coupler

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 —
Rhi High reflection R Ω — 4 sig —
Rlo Low reflection R Ω — 4 sig —
RhiE96 High E96 Ω — 4 sig —
RloE96 Low E96 Ω — 4 sig —
Γ Reflection coefficient — — 4 sig —
Pres Resistor dissipation (approx) 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 10.12 dB
Zin · Input impedance 50 Ω
Rhi · High reflection R 96.25 Ω
Rlo · Low reflection R 25.97 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 reflection attenuator is two resistors hanging off a 90° hybrid, not a three-resistor through pad. The page will not let you forget the hybrid. Ideal Rhigh/Rlow, nearest E96, and |Γ| are listed together.

Pitfalls

  • Building the resistors without a 90° hybrid. This is not a through pad.
  • Trusting A above 60 dB; parasitics dominate.
  • Confusing Rhigh with a π-pad shunt — the network is different.

FAQ

Do I need a hybrid coupler?

Yes. A reflection attenuator presents Rhigh and Rlow on the coupled ports of a 90° hybrid.

What resistors make 10 dB in 50 Ω?

About 96.2 Ω and 26.0 Ω.

Why two resistors instead of three?

The hybrid provides the match. The resistors set |Γ| = (K−1)/(K+1).

Is A = 0 allowed?

No. K = 1 makes Rhigh infinite.

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