# VSWR in transmission line.

#### AndrieGnd

Joined Jun 25, 2019
52
Hi guys, I'm confused about term " VSWR " on transmission line.
what I'm confusing about, VSWR looks like coefficient reflection ..so what's the difference between them?!

Can anyone please explain it to me in a simple meaningful explanation?

thanks alot.

#### nsaspook

Joined Aug 27, 2009
6,283
First, see what it means with physical waves.

http://www.antenna-theory.com/tutorial/txline/transmission3.php
One thing that becomes obvious is that the ratio of Vmax to Vmin becomes larger as the reflection coefficient increases. That is, if the ratio of Vmax to Vmin is one, then there are no standing waves, and the impedance of the line is perfectly matched to the load. If the ratio of Vmax to Vmin is infinite, then the magnitude of the reflection coefficient is 1, so that all power is reflected. Hence, this ratio, known as the Voltage Standing Wave Ratio (VSWR) or standing wave ratio is a measure of how well matched a transmission line is to a load.

#### Papabravo

Joined Feb 24, 2006
12,405
The reflection coefficient is a complex quantity. It is normally calculated as the quotient of the difference between load and source impedance and the sum of load and source impedance. It varies, on the real axis, from -1 to +1. SWR on the other hand uses just the magnitude of the reflection coefficient:

$$VSWR\;=\;\frac{1+|\Gamma|}{1-| \Gamma |}$$

VSWR is always a real number because we have taken the magnitude of a complex number and it is always positive.