Small-signal
Complex impedance, reflection, and a Smith chart at the measurement reference plane.
Z₀ the reference impedance everything is normalised toZ = R + jX the load being described
Enter R + jX, or |Γ| and phase. Blank R, X, or phase means zero. Editing S11, VSWR, or mismatch loss keeps the reflection phase. Magnitude alone does not determine complex impedance.
Drag the marker or click the chart. Arrow keys move Γ; Shift makes a fine adjustment.
Upper half: inductive (+jX). Lower half: capacitive (−jX). Grid values are normalized to Z₀.
This slice has X = 0. Click it to set a real resistance.
Two reflections facing each other, such as this load and the analyzer port, interact through the product of their reflection coefficients. The trace moves between 20 log₁₀(1 ± |Γ₁Γ₂|) as the phase between them turns with frequency. Blank Γ₁ uses this load.
Order-of-magnitude only
| Item | Thumb | Why it matters |
|---|---|---|
| Return loss 10 dB | VSWR 1.92 · 0.46 dB lost | Often acceptable; the lost power is rarely what hurts |
| Return loss 14 dB | VSWR 1.50 · 0.18 dB | A common connector and cable specification |
| Return loss 20 dB | VSWR 1.22 · 0.04 dB | Good match; going further buys almost no power back |
| Return loss 26 dB | VSWR 1.11 · 0.01 dB | Calibration-grade, and hard to hold over a wide band |
| VSWR 2 | RL 9.5 dB · 0.51 dB | The classic acceptable limit still costs half a decibel |
| Two mismatches face to face | ripple ±20 log₁₀(1 ± |Γ₁||Γ₂|) | Two 20 dB returns ripple ±0.09 dB; two 10 dB returns ripple ±0.9 dB |
| Why match actually matters | ripple and uncertainty, not loss | The interaction between two mismatches beats the power either one wastes |
Passive impedances (R ≥ 0), real positive Z₀. Γ = (Z − Z₀)/(Z + Z₀). Delivered power fraction is 1 − |Γ|² for a matched source at this plane. This is not a full source/load mismatch uncertainty model.
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