What is VSWR?
Many of us know that, a bad VSWR affects the network's performance. But what about you: do you know what it means?
VSWR stands for Voltage Standing-Wave Ratio. It is a measure used to determe the severity of standing waves in a transmission line. Standing waves form when there is a mismatch between the line and the load, it is generally undesirable. The reflection coefficient is another measure closely related to VSWR. Engineers use the reflection coeffcient to determine how much of the signal propagating on a line is reflected back to the source. Return loss can measure how much of the signal is lost when it is reflected back to the source, matching loss is the loss incurred when there is a great mismatch btw the line and the load.
Applications
VSWR is a parameter used by engineers to know the degree of mismatch between a transmission line and a device (like an antenna or a transmitter/receiver circuit). The presence of standing waves in a transmission line means part of the incident signal is being reflected back to the source. The ratio of reflected voltage to the incident voltage is the reflection coefficient. That means that all the incident voltage is reflected back. A reflection coefficient equal to one would result in a VSWR equal to infinity. Therefore, the higher VSWR, the greater the reflection and consequently the higher the degree of mismatch between the line and the load.
The return loss and mismatch loss are parameters can indicate how much of the signal is lost because of the line mismatch. Engineers are used to seeing the power losses in dB, thus having parameters presented in dB is more convenient than ratios (like what the VSWR and reflection coefficient are). For example, instead of saying that the reflection coefficient in the line is 0.8, the engineers would rather say that the signal suffered a return loss of 1.938 dB.
Conclusion
We can then understand that, VSWR as an indicator of signal reflected back to the transmitter radio frequency, always taking the value 1 in the denominator. And the lower this index, the better! A radio frequency system with 1.4:1 VSWR is better than 1.5:1. Finally, the VSWR in a radio frequency system can be measured by special equipment.