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Bridged-Tee Attenuator Calculator

A 10 dB bridged-tee for 50 Ω keeps the arms at 50 Ω; Rbridge = 108.1 Ω, Rshunt = 23.12 Ω.

By Jasper · Updated

Calculator

PASS10.00 dBE96 9.953 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
23.12 Ω
R bridge
108.11 Ω
R arm (exact Z0)
50 Ω
Zin
50 Ω
Ideal att
10.00 dB
R shunt E96
23.2 Ω
R bridge E96
107 Ω
E96 Zin
49.92 Ω
E96 att
9.953 dB
Return loss
∞
E96 return loss
62.32 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

Bridged-Tee Attenuator Calculator

Rarm=Z0,Rbr=Z0(K-1),Rsh=Z0/(K-1) arms = Z0; Rbr = Z0(K−1); Rsh = Z0/(K−1)

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 —
Rarm Arm resistor Ω — 4 sig —
Rbr Bridge resistor Ω — 4 sig —
Rsh Shunt resistor Ω — 4 sig —
RbrE96 Bridge E96 Ω — 4 sig —
RshE96 Shunt E96 Ω — 4 sig —
Pbr Bridge dissipation W — 4 sig —
ParmIn Input arm dissipation W — 4 sig —
ParmOut Output arm dissipation W — 4 sig —
Psh 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 9.953 dB
Zin · Input impedance 50 Ω
Rarm · Arm resistor 50 Ω
Rbr · Bridge resistor 108.1 Ω
Rsh · Shunt resistor 23.12 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 bridged-T is the pad you reach for when you want to change attenuation without restuffing the through-line resistors. The arms stay at Z0; only the bridge and shunt move. E96 snapping follows that split.

Pitfalls

  • Snapping the arms to E96. This page keeps them at exact Z0 so the pad stays closer to matched.
  • Trusting A above 60 dB; parasitics dominate.
  • Wiring the bridge across the wrong nodes.

FAQ

What is special about a bridged-T?

The two arms stay at Z0. You only change the bridge and the shunt when you change A.

Do the arms snap to E96?

No. They stay at exact Z0. Only Rbridge and Rshunt snap.

What is 10 dB / 50 Ω?

Arms 50 Ω, bridge 108 Ω, shunt 23.1 Ω.

Why warn above 60 dB?

Lumped pads at that ratio are theoretical; layout parasitics take over.

Related

Sources