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RF Attenuator Calculator – Pi & T Pads
Calculate symmetrical RF attenuator resistor values for Pi and T pads from attenuation, system impedance, and input power. Includes voltage ratio, power ratio, and output power.
Input Parameters
Results
Use RF-rated resistors and layout. At high frequency, resistor parasitics, PCB geometry, connectors, and power handling strongly affect performance.
Equations Used
K = 10^(Attenuation dB / 20)
Pi pad: shunt resistors = Z0 × (K + 1)/(K - 1); series resistor = Z0 × (K² - 1)/(2K)
T pad: series resistors = Z0 × (K - 1)/(K + 1); shunt resistor = 2 × Z0 × K/(K² - 1)
Output power dBm = Input power dBm - attenuation dB
Frequently Asked Questions (FAQ)
Q1: What does an RF attenuator calculator do?
It calculates resistor values for impedance-matched Pi and T attenuator pads.
Q2: What is the difference between Pi and T attenuators?
A Pi pad uses two shunt resistors and one series resistor; a T pad uses two series resistors and one shunt resistor.
Q3: Can I use standard resistors for RF attenuators?
At low frequencies yes, but RF designs need low-parasitic resistors, short layout, and correct impedance geometry.
Q4: Does this calculator support 50 ohm and 75 ohm systems?
Yes. Enter the desired system impedance such as 50 Ω for RF or 75 Ω for video/coax systems.
Q5: Why does high attenuation produce extreme resistor values?
Large attenuation ratios require resistor values that may become impractical or sensitive to parasitics and tolerance.
