Resistive Attenuator (T / Pi Pad) Calculator

A resistive pad reduces signal level by a fixed amount while keeping the line matched to Z₀. Let K = 10^(dB/20).

• T-pad: R1 = Z₀(K−1)/(K+1), R2 = Z₀·2K/(K²−1)
• Pi-pad: R1 = Z₀(K+1)/(K−1), R2 = Z₀(K²−1)/(2K)

Usage: Enter the attenuation and system impedance (50 Ω for most RF). Pick the T or Pi topology that gives the most buildable resistor values.

When you need it: Designing a matched resistive pad that drops signal level by a set number of dB while keeping the line at its characteristic impedance (usually 50 Ω).

Worked example: A 6 dB 50 Ω Pi pad uses a series R ≈ 37 Ω between two shunt Rs ≈ 150 Ω. The voltage ratio is 10^(dB/20), and the pad presents 50 Ω at both ports.

Tips & gotchas:

• Resistive pads are broadband and dead simple, but they dissipate the attenuated power as heat.
• T topology suits low attenuation; Pi is common at 50 Ω — both are matched two-ports.
• The input resistor sees the most power; rate it for the full input level at high drive.
• A pad also improves source/load match — a few dB of padding is a cheap VSWR fix.