Overview

Reflection coefficient ( ?), return loss (RL), and voltage standing wave ratio (VSWR) are related. The most commonly used parameter in device specifications, however, is VSWR.

Using an S-parameter-based definition, input and output reflection coefficients are defined [1] as follows:

(B.1)

or

(B.2)

If the DUT is impedance matched to the test equipment, then the reflection coefficient of the source and load become zero and the input and output reflection coefficients of the DUT are simply the magnitude of S ₁₁ or S ₂₂ (referring to either the input reflection coefficient or output reflection coefficient, respectively):

(B.3)

or

(B.4)

The relationship between the reflection coefficient and return loss is

(B.5)

The relationship between VSWR and the reflection coefficient is

(B.6)

and it therefore follows that VSWR is related to reflection coefficient by

(B.7)

The acronym VSWR is often pronounced as a word, "vis-war," rather than as the acronym that it is. Additionally, it is most often written as a ratio, relative to 1, as shown in the Table B.1. This table shows the relationship between VSWR, return loss, and reflection coefficient.