VSWR Mismatch Errors

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VSWR Mismatch Errors

Both amplitude and phase errors are introduced when mismatched impedances are present at an electrical interface. The result is ripple across the frequency band (since the VSWR of each interface typically varies with frequency), as well as a portion of the incident power being reflected back to the source.

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Amplitude ErrorPhase Error
eA = 20 * log (1 ± |GA * GB|) dBef = (180 / p) *| GA| * |GB|

Note: This formula has also been seen written as ef = (180 / p) * sin-1 (| GA| * |GB|),
           but for small angles, the difference is negligible

See a derivation of this equation as provided by Haris Tabakovic

Resultant MIN and MAX Cascaded VSWR
VSWRMAX = SA * SB
VSWRMIN = SA / SB
 

where

SA = larger of the two VSWRs
SB = smaller of the two VSWRs

Example

VSWRA = 2.5:1  -->  SA = 2.5
VSWRB = 2.0:1  -->  SB = 2.0
VSWRMAX = 2.5 * 2.0 = 5.0  = 5.0:1
VSWRMIN = 2.5 / 2.0 = 1.25  = 1.25:1