VSWR & Return Loss Calculator
ZCG antennas are typically factory tuned to better than 1.5:1 VSWR across their rated band, and our installation guides recommend measuring return loss or VSWR at the feeder cable input once your antenna is mounted and connected, before you apply full transmit power. This calculator does that check for you.
Enter the forward and reflected power straight from your wattmeter to get VSWR, return loss, match efficiency and reflection coefficient (Γ) in one step. If you already have one of these figures from a spec sheet or a sweep, the second tool converts between all four without you needing to do the maths by hand. The third tool converts your transmitter's output between watts and dBm.
1Power → VSWR / Return Loss / Match
INForward Power
Watts
INReflected Power
Watts
VSWR
—
Return Loss
—dB
Match Efficiency
—%
Rho (Γ)
—
—
VSWR
Pf = Forward Power (W) · Pr = Reflected Power (W)
VSWR = [1+√(Pr/Pf)] / [1−√(Pr/Pf)] · Return Loss = 10·log(Pr/Pf) dB · Match Eff. = 100·(1−Pr/Pf) % · ρ = √(Pr/Pf)
VSWR = [1+√(Pr/Pf)] / [1−√(Pr/Pf)] · Return Loss = 10·log(Pr/Pf) dB · Match Eff. = 100·(1−Pr/Pf) % · ρ = √(Pr/Pf)
2Match Quantity → All Equivalents
INQuantity Type
INValue
ratio
VSWR
—
Return Loss
—dB
Match Efficiency
—%
Rho (Γ)
—
Select any one match-quality quantity and enter its value — the other three are computed automatically.
Conversions derived from: VSWR = (1+ρ)/(1−ρ) · RL = 20·log(ρ) · Match Eff. = 100·(1−ρ²)
Conversions derived from: VSWR = (1+ρ)/(1−ρ) · RL = 20·log(ρ) · Match Eff. = 100·(1−ρ²)
3Power Unit Conversion (Watts ↔ dBm)
Watts → dBm
Watts
Power
—dBm
dBm → Watts
dBm
Power
—W
Power (dBm) = 10·log[Power (W)] + 30 · Power (W) = 10^[(dBm−30)/10]
iReference & Definitions
VSWR — Voltage Standing Wave Ratio
Pf — Forward Power (W)
Pr — Reflected Power (W)
ρ (Rho) — Reflection Coefficient Magnitude
VSWR from power
[1 + √(Pr/Pf)] / [1 − √(Pr/Pf)]
VSWR from ρ
(1 + ρ) / (1 − ρ)
Return Loss from power
10 · log(Pr / Pf) dB
Return Loss from VSWR
10 · log{[(VSWR−1)/(VSWR+1)]²} dB
Match Efficiency from power
100% · (1 − Pr/Pf)
Match Efficiency from VSWR
100% · [1 − ((VSWR−1)/(VSWR+1))²]
Rho from power
√(Pr / Pf)
Power: Watts → dBm
10 · log(W) + 30
