Pi-Pad Shunt Resistor

R1 = Z · (K + 1)/(K − 1)

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Result
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Formula

R1 = R3 = Z × (K + 1)/(K − 1)

Description

The two equal shunt resistors of a symmetric Pi-pad attenuator connect each port to ground. This formula gives each shunt arm. As attenuation increases the shunt resistors fall toward Z, while the series resistor rises—the opposite trend to the T-pad and a useful way to keep resistor values in a practical range.

Variables

  • R1 — Each shunt resistor to ground (Ω)
  • Z — Characteristic impedance (Ω)
  • dB — Desired attenuation; K = 10^(dB/20)

Practical Notes

Combine with the Pi-pad series resistor R2 = Z(K²−1)/(2K). For low attenuation the shunt arms become large (near open) and the pad approaches a through connection.

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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