Reflection Coefficient Calculator

How it is calculated

Inputs are the load impedance ZL and the line characteristic impedance Z0, both in ohms and both treated as purely resistive (real) values. The reflection coefficient is Γ = (ZL − Z0) / (ZL + Z0). From its magnitude |Γ| the tool derives VSWR = (1 + |Γ|) / (1 − |Γ|), return loss = −20·log10|Γ| in dB, and the share of reflected power |Γ|² × 100 in percent.

Γ is signed: positive when the load is above the line impedance, negative when below. A perfect match (Z_L = Z₀) gives Γ = 0, VSWR = 1.000 and return loss ∞ dB. A short circuit (Z_L = 0) gives Γ = -1, VSWR ∞ and 0 dB return loss. Z_L must be zero or more and Z₀ above zero; otherwise there is no result. Reactive loads with a phase angle (complex impedance) cannot be entered.

Common mistakes

• Swapping the load and the line: Γ then changes sign (a 25 ohm load on a 50 ohm line gives -0.3333), although |Γ|, VSWR and return loss stay the same. Enter the load as Z_L and the line as Z₀.
• Reading a larger return loss as worse: return loss in dB is higher when the match is better, so 13.979 dB is better than 9.542 dB.
• Confusing the magnitude with the signed value: the Γ line keeps the minus sign, while the |Γ| line is always positive. VSWR and return loss use only the magnitude.
• Entering a complex antenna impedance such as 50 + j25: only the real value can be typed, so reactance is ignored and the result describes a purely resistive load.
• Entering 0 for the line impedance or a negative load: both return no result, because a transmission line needs a positive characteristic impedance and the tool handles only passive resistive loads.