Reflection Attenuator Calculator

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This simple tool helps RF beginners, hobbyists, and engineers see how much of a signal is “bouncing back” when impedances don’t match. Enter your system’s characteristic impedance (e.g. 50 Ω) and load impedance (and, optionally, incident/reflected power levels), and it will compute the reflection coefficient, VSWR, return loss, and attenuation. These metrics tell you how much power is reflected by an impedance discontinuity. A low reflection coefficient (close to 0) and high return loss (large dB value) indicate a good match, meaning most power is delivered to the load.

FAQ

What is a reflection attenuator?
An attenuator is a circuit that reduces signal power. A reflection attenuator does this by both absorbing some energy and reflecting some back to the source

Why is VSWR important?
VSWR tells you how efficiently power is transferred through your system. A low VSWR (close to 1:1) means almost all the power reaches the load. A high VSWR means much of the energy is reflected, which can damage transmitters or waste power. 

What values should I enter?
Enter the characteristic impedance of your transmission line (e.g. 50 Ω) and the impedance of your load (in the same units). If you have power measurements, you can also enter the incident (forward) power and reflected power. The calculator uses these to compute the reflection coefficient, VSWR, return loss, and the resulting attenuation (loss). 

What is a good return loss value?
Generally, higher return loss is better (meaning less reflection). As a rule of thumb, a return loss of 20 dB or more is considered good: that means only about 1% of the power is reflected.