Pi-Pad Series Resistor

R2 = Z · (K² − 1) / (2K)

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Result
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Formula

R2 = Z × (K² − 1) / (2K)

Description

A Pi-pad attenuator uses two shunt resistors and one series resistor arranged like the Greek letter π. This formula gives the single series (bridging) resistor. The Pi topology is the dual of the T-pad and is often preferred when the bridging resistor value is more convenient or when matching to a transmission line whose impedance suits the shunt-heavy structure.

Variables

  • R2 — Series (bridging) resistor (Ω)
  • Z — Characteristic impedance (Ω)
  • dB — Desired attenuation; K = 10^(dB/20)

Practical Notes

Pair with the Pi-pad shunt resistors R1 = R3 = Z(K+1)/(K−1). T and Pi pads give identical attenuation and matching; choose whichever yields nicer resistor values.

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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