T-Pad Shunt Resistor

R3 = 2 · Z · K / (K² − 1)

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Result
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Formula

R3 = 2 × Z × K / (K² − 1)

Description

The shunt (middle) resistor of a symmetric T-pad attenuator connects the junction of the two series arms to ground. Together with the series arms it sets both the attenuation and the matched impedance. As attenuation rises (larger K), the shunt resistor falls, diverting more signal to ground.

Variables

  • R3 — Shunt resistor to ground (Ω)
  • Z — Characteristic impedance (Ω)
  • dB — Desired attenuation; K = 10^(dB/20)

Practical Notes

Use together with the T-pad series arms R1 = R2 = Z(K−1)/(K+1). For very high attenuation the shunt resistor becomes small and the series arms approach Z.

Related Concepts

All Attenuators & Pads formulas →
Attenuation Factor (K) T-Pad Series Resistor T-Pad Shunt Resistor Pi-Pad Series Resistor Pi-Pad Shunt Resistor Bridged-T Bridge Resistor Bridged-T Shunt Resistor

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