EMC Question of the Week: December 9, 2019

At a discontinuity in a transmission line, the ratio of incident power to reflected power in decibels is generally referred to as the

1. reflection coefficient
2. transmission coefficient
3. insertion loss
4. return loss

Answer

The best answer is "d". The ratio of incident power to reflected power is the return loss. This value, expressed in dB, is always a non-negative number. Return loss is a measure of how well devices or lines are matched. A match is good if the return loss is high. 

Occasionally, in the published literature, the S-parameter, S₁₁, is labeled return loss, but this is incorrect. S₁₁ is equal to the reflection coefficient at Port 1. Expressed in decibels, the reflection coefficient is the negative of the return loss.

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