Insertion Loss vs Return Loss


Insertion loss and return loss are two different parameters used in the context of signal transmission and measurements, particularly in the field of telecommunications and electronics.

They measure different aspects of signal behavior.

Here’s a brief explanation of each and the key differences between them:

Insertion Loss

Insertion loss refers to the reduction in signal power or energy when a component, device, or system is inserted into a transmission path. It quantifies how much of the signal’s power is lost as it passes through a component or system.

Insertion loss is typically expressed in decibels (dB).

???? A lower insertion loss value indicates less signal power is lost, making it more desirable in most cases. An exception is in the case of filters – signals to be rejected should have a high insertion loss.

Components like cables, connectors, filters, switches, and amplifiers can introduce insertion loss as the signal passes through them.

???? Try the insertion loss calculator to understand how it varies with input and output power.

Return Loss

Return loss measures the amount of signal that is reflected back towards its source when it encounters an impedance mismatch or a discontinuity in the transmission path.

Return loss is also expressed in decibels (dB).

???? Higher return loss values are typically more desirable. A higher return loss indicates that less signal is reflected back towards the source. This means better impedance matching and less signal loss due to reflections. As with insertion loss, a filter should have low return loss values at out-of-band signal frequencies.

Return loss is particularly important in applications like RF (radio frequency) and microwave systems, as well as in high-frequency digital signal transmission, where impedance matching is critical to minimize signal distortion.

Return Loss vs Insertion Loss of a Band Pass Filter

The plot below shows Insertion Loss (S21) and Return Loss (S11) of a BPF.

  • The absolute value of S21 is equal to the insertion loss. It is minimum in the passband.
  • The return loss (absolute value of S11) is minimum out of band and maximum in the pass band.


In summary, the main difference between insertion loss and return loss is what they measure:

  • Insertion loss measures the signal power lost as it passes through a component or system.
  • Return loss measures the signal reflected back towards its source due to impedance mismatches or discontinuities in the transmission path.

Both parameters are important for ensuring signal integrity and efficient signal transmission in various electronic and communication systems, but they focus on different aspects of signal behavior.

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