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About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2016
Webmaster:
Kirt Blattenberger,
 BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

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Directional Coupler Calculator

These directional couplers calculations are based on textbook equations and conditions where all four ports are assumed to be terminated in impedances that are exactly matched to the characteristic impedance of the coupler, and that perfectly linear operation occurs. The "Directivity" term accounts for non-ideal isolation between the coupler input and the isolated port. The "Mainline Loss" term exists to account for resistive losses in the coupler (a specification often provided by the manufacturer).

Definitions for all of the terms used are provided below the calculator. Mainline Loss and Coupling Factor can be entered as positive or negative according to your preferred standard, but the results are the same for either since the absolute value is used.

Calculated values do not change until the "Calculate" button is clicked.

  Mainline Loss  
  dB  
Input (Port 1) Transmitted (Port 2) Coupling Losses Only
dBm dBm dB
Coupling Factor Directivity Isolation
dB dB dB
     
Coupled (Port 3) Isolated (Port 4)  
dBm dBm  

Input (Port 1) Main system signal input (sign depends on power level)
Transmitted (Port 2) Main system signal output  (sign depends on power level)
Coupled (Port 3) Power sampled from Port 1 (forward, or incident)  (sign depends on power level)
Isolated (Port 4) Power sampled from Port 2 (reverse, or reflected)  (sign depends on power level)
Coupling Factor Amount of power sampled relative to the input (always positive dB)
Mainline Loss Resistive losses not due to coupling (always positive dB)
Directivity Difference between Port 3 and Port 4 (always positive dB)
Isolation Difference between Port 1 and Port 4 (always positive dB)
Coupling Losses Only Theoretical reduction in output power relative to the input due to power lost to the coupled and isolated ports. (always positive dB)