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Voltage standing wave ratio (VSWR) (pronounced "vizwar" [1] [2]) is the ratio of maximum to minimum voltage on a transmission line . For example, a VSWR of 1.2 means a peak voltage 1.2 times the minimum voltage along that line, if the line is at least one half wavelength long.
The blue circle, centered within the impedance Smith chart, is sometimes called an SWR circle (short for constant standing wave ratio). The complex voltage reflection coefficient Γ {\displaystyle \Gamma \,} is defined as the ratio of the reflected wave to the incident (or forward) wave.
The input impedance is slowly varying over this wide frequency range, allowing low voltage standing wave ratio (VSWR) over the bandwidth. [1] The gain of horn antennas ranges up to 25 dBi, with 10–20 dBi being typical. [1]
A standing wave ratio meter, SWR meter, ISWR meter (current "I" SWR), or VSWR meter (voltage SWR) measures the standing wave ratio (SWR) in a transmission line. [ a ] The meter indirectly measures the degree of mismatch between a transmission line and its load (usually an antenna ).
It is usually expressed as a ratio in decibels (dB); = where RL(dB) is the return loss in dB, P i is the incident power and P r is the reflected power. Return loss is related to both standing wave ratio (SWR) and reflection coefficient (Γ). Increasing return loss corresponds to lower SWR.
It is a common misconception that a high standing wave ratio (SWR) per se causes loss. [3] A well-adjusted ATU feeding an antenna through a low-loss line may have only a small percentage of additional loss compared with an intrinsically matched antenna, even with a high SWR (4:1, for example). [21]
In telecommunications and transmission line theory, the reflection coefficient is the ratio of the complex amplitude of the reflected wave to that of the incident wave. The voltage and current at any point along a transmission line can always be resolved into forward and reflected traveling waves given a specified reference impedance Z 0.
The gain relative to an isotropic antenna (dBi), front-to-back ratio, standing wave ratio and the general reception pattern are all evident from these numbers. [15] Programs often process this into more common forms like Smith charts. [16]