What does the VSWR indicate in a transmission line?

The VSWR, or Voltage Standing Wave Ratio, is a crucial measurement in transmission line theory that quantifies power reflection. It is a ratio that describes how well the load impedance matches the characteristic impedance of the transmission line. When there is a mismatch, some of the incident power is reflected back toward the source, instead of being transmitted to the load.

A high VSWR indicates a significant level of reflected power, suggesting that the impedance mismatch is substantial. Conversely, a low VSWR shows that most of the power is being transmitted effectively to the load with minimal reflection. Hence, the VSWR serves as a direct measurement of how much of the signal power is being reflected due to impedance mismatches in the system. This makes it an essential parameter for determining the efficiency of power transfer in a transmission line.

In this context, while signal quality, matching efficiency, and signal frequency are important concepts related to transmission lines, they do not directly indicate the reflection of power, which is the primary function of the VSWR.