RF Pi Attenuator Calculator

Use this tool to calculate Resistor values for a Pi attenuator.

Enter the desired value of attenuation and the characteristic impedance (default value is 50 ohm).

Formula

R1 = Zo [10dB/20 + 1] / [10dB/20 – 1]

R2 = Zo/2 [10dB/10 – 1] / [10dB/20]

where R1 is the shunt resistor and R2 is the series resistor. To build this attenuator you will need

• two shunt resistors – one at the input and the other at the output
• one series resistor

Example Calculation

A 10 dB attenuation can be realized with the following values:

• R1 = 96.25 Ω
• R2 = 71.15 Ω

Assuming input and output impedance is 50 Ω

What is a Pi Attenuator?

A Pi attenuator is a type of passive electronic attenuator that uses a configuration resembling the Greek letter π (pi) in its circuit diagram. It is composed of three resistors: two series resistors and one shunt resistor that connects the series resistors at the midpoint to the ground or common circuit. This design is commonly used in RF (Radio Frequency) circuits to reduce signal levels, match impedances between circuits, and maintain signal integrity.

The primary advantage of a Pi attenuator is its ability to provide a relatively constant impedance match in both directions across its terminals, which is crucial in high-frequency applications to prevent signal reflections that can distort the signal. The attenuation level, which is the amount by which the signal is reduced, is determined by the values of the resistors. The design allows for easy adjustment of these resistor values to achieve the desired level of attenuation.

Pi attenuators are widely used in various applications, including telecommunications, radio and television broadcasting, and any other scenario where signal level reduction without significant reflection or distortion is required. They are appreciated for their simplicity, effectiveness, and the ease with which they can be integrated into different circuit designs.