Balanced Attenuator Calculator

What is attenuator?

An attenuator is a two-port device used in series with the signal source and load to reduce the signal's power without appreciably distorting signal waveform provided that the attenuator’s impedance is matched with the input source’s and load’s impedances. For example, the attenuator is used to lower the amplitude of the signal to the desired value to enable measurements or to protect the measuring device from signal levels that might damage it. The attenuator is also called a pad. The attenuators are suitable for use in radio, electronic circuits, communication, and transmission line applications to weaken a stronger signal. Attenuators are usually passive devices that use resistive networks to attenuate the signal. The basic types of passive attenuators are L type, pi (π) type, and T type attenuators. Active type attenuators are also available.

What is a balanced attenuator?

A passive attenuator is called a balanced attenuator when the two transmission lines of the attenuator have equal impedances along their lengths with respect to ground. Balanced attenuators are symmetrical attenuators, which means a symmetrical attenuator has the same value of the characteristic impedance (Zo = V/I) at the input, and output sides, allowing for its input and output terminals to be transposed with each other.

Thus, the balanced attenuator is suitable to connect in series with a signal source and load to reduce the signal power when the source impedance (ZS) and load impedance (ZL) are equal (i.e., ZS = ZL = Zo). Here, Zo represents the characteristic impedance of the balanced attenuator.

The following fig shows a balanced attenuator. Here, we can see that both the line has same impedance value (R1=R1) and same characteristic impedance (Zo) at both input and output sides, thus, it is a balanced attenuator circuit. Other examples of balanced attenuators are the "H"-pad and “O” pad.

How to calculate the resistance in balanced attenuator?

This calculator is used to calculate the value of resistor R1 of balanced attenuator (shown below) for the required value of attenuation (in dB) and for matching impedance/characteristic impedance (Zo = Zs =ZL Ω). Here, Zo is the characteristic impedance of balanced attenuator, which is equal to the value of source (Zs) and load impedance (ZL).

The following formula is used to calculate the value of resistor R1 balanced attenuator (shown above) for the desired value of attenuation (dB) and matching impedance/characteristic impedance (Zo Ω).

• Where:
• R1 (Ω) = Value of resistor in the balanced attenuator
• Zo = Characteristic impedance of the balanced attenuator (shown above) in Ω
• dB = Required attenuation level in dB (i.e., decibels)