Calculate coupler coupling factor, through-path loss, isolation, and directivity from S-parameters. Interactive calculator for 10 dB, 20 dB, and 3 dB couplers in 50Ω systems.
Interactive Coupler Calculator
Coupler Performance Calculator
Coupling factor S31 (dB)
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Coupled power fraction
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Through-path S21
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Through-path loss
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Isolation S41
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Directivity
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Coupler Design Reference
Coupling
S31
Coupled %
Through Loss (S21)
3 dB coupler
−3.01 dB
50.0%
−3.01 dB
6 dB coupler
−6.02 dB
25.0%
−1.25 dB
10 dB coupler
−10.0 dB
10.0%
−0.46 dB
20 dB coupler
−20.0 dB
1.0%
−0.04 dB
30 dB coupler
−30.0 dB
0.1%
−0.004 dB
Directivity Formula
Directivity = Isolation − Coupling = |S41_dB| − |S31_dB|
Good coupler: Directivity > 25 dB
For VSWR measurement: Directivity limits minimum measurable |Γ|
Directivity 30 dB → min measurable |Γ| = 0.032 → min VSWR = 1.065
RF View Coupler Analysis: Load coupler .s4p, extract S31 (coupling), S21 (through), S41 (isolation) port pairs. Directivity = |isolation dB| − |coupling dB|, read with delta marker. Free on Android.