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RF Attenuator Calculator – Pi and T Pads
Calculate ideal resistor values for matched Pi and T RF attenuator pads, with approximate nearest E24 resistor suggestions.
Input Parameters
Results
Use precision resistors and RF layout practices for best return loss.
Equations Used
Voltage Ratio:
K = 10^(attenuation dB / 20)
Pi Pad Series Resistor:
Rseries = Z0 × (K² - 1) / (2K)
Pi Pad Shunt Resistors:
Rshunt = Z0 × (K + 1) / (K - 1)
T Pad Series Resistors:
Rseries = Z0 × (K - 1) / (K + 1)
T Pad Shunt Resistor:
Rshunt = 2 × Z0 × K / (K² - 1)
Frequently Asked Questions (FAQ)
Q1: What does this RF attenuator calculator do?
It calculates resistor values for matched Pi and T attenuator pads.
Q2: What impedance should I use?
Use the system impedance, usually 50 ohms for RF or 75 ohms for video and some RF distribution systems.
Q3: What is the difference between Pi and T pads?
Both can provide matched attenuation, but their resistor arrangements and practical resistor values differ.
Q4: Can I use standard resistor values?
Yes, but standard values introduce small mismatch and attenuation error. This tool gives approximate E24 suggestions.
Q5: Does this include resistor parasitics?
No. At high frequency, resistor package parasitics and PCB layout affect performance.
Q6: Can this be used for high power?
Check resistor power ratings and temperature rise. High-power attenuators need thermal design.
