Your RF Cafe
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.
|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)|