Reflection Attenuator Calculator

Enter the Impedance and required attenuation level to get values for R1 < Zo(Ω) and R1 > Zo(Ω)

  • dB
  • Ω


  • R1 < Zo
  • R1 > Zo
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Reflection attenuator calculator:

A reflection attenuator uses a reflective technique in addition to the absorption technique to reduce the signal’s power without appreciably distorting the signal waveform.

This online reflection attenuator calculator allows the user to calculate the two possible resistor values (R1< Z0 & R1> Z0) of a reflection attenuator by entering the required attenuation level (in dB) and the characteristic impedance Z0 (in Ω) of the reflection attenuator.

An attenuator is a device used between the signal source and load to reduce the signal's power without appreciably distorting signal waveform, as well as the attenuator provides impedance matching between the input source and load. 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.

A reflection attenuator uses a reflective technique in addition to absorption (i.e., heat) to reduce the signal’s power. Hence, a reflective attenuator attenuates the signal as well as reflects some portion of the input power back to the driving source. The amount attenuation level determines the amount of reflected power.

A high VSWR (voltage standing wave ratio) is a problem in reflective type attenuators when compared to the absorptive (non-reflective) type attenuators. Hence, usually, the designers prefer a non-reflective type attenuator. Voltage standing wave ratio (VSWR) is the measure of impedance mismatching between two connected lines. If VSWR is high, it means that a high impedance mismatch results in high reflected power. The following figure shows the passive reflection attenuator that uses resistive elements.

Reflection attenuator
Reflection attenuator

How to calculate resistance of reflection attenuator?

The formulas for calculating the value of resistor R1of reflection attenuator (shown above) for the required value of attenuation (in dB) and for the characteristic impedance (Zo) is given below. This calculator provides two values of resistor in ohm – one is less than characteristic impedance and another one is greater than characteristic impedance by using the following formulas.

  • Where:
  • R1 (Ω) < Zo = Value of resistor which is less than Zo
  • R1 (Ω) > Zo = Value of resistor which is greater than Zo
  • Zo = Characteristic impedance of the reflection attenuator (shown above) in Ω
  • dB = Required attenuation level in dB (i.e., decibels)