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VSWR Mismatch Errors

Amplifier SolutionsRes-Net MicrowavePlease click here to visit the NP Technologies websiteClick to visit the RFtronics website


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. Here is a well-done reflection coefficient video tutorial by SavvyPaper.

VSWR Mismatch Errors - RF Cafe


Here is a JavaScript calculator for VSWR / Return Loss / Reflection Coefficient / Mismatch Error / Improvement.

 

Amplitude ErrorPhase Error
εA = 20 * log (1 ± |ΓA * ΓB|) dBεΦ = (180 / π) *| ΓA| * |ΓB|

Note: This formula has also been seen written as

            εΦ= (180 / π) * 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

 

RF Cafe Software

RF Cascade Workbook
 RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

Smith Chart™ for Excel
Smith Chart™ for Visio
RF & EE Symbols Word
RF Stencils for Visio
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