For a 50 Ω transmission line terminated with ZL = 25 Ω, which option correctly states Γ and SWR?

• A. Γ = (25−50)/(25+50) = −0.333; |Γ| = 0.333; SWR ≈ 2.0
• B. Γ = (50−25)/(50+25) = 0.333; |Γ| = 0.333; SWR ≈ 1.5
• C. Γ = (ZL−Z0)/(ZL+Z0) with ZL=25, Z0=50
• D. Γ = (ZL+Z0)/(ZL−Z0) with ZL=25, Z0=50

Answer: (A)

On a transmission line, the reflection coefficient is Γ = (ZL − Z0) / (ZL + Z0). With Z0 = 50 Ω and ZL = 25 Ω, this becomes Γ = (25 − 50) / (25 + 50) = (−25) / 75 = −0.333. The magnitude is |Γ| = 0.333, which gives the standing-wave ratio SWR = (1 + |Γ|) / (1 − |Γ|) = 1.333 / 0.667 ≈ 2.0. The negative sign indicates the load is smaller than the line impedance, so the reflected wave is inverted in phase. Thus Γ is about −0.333 and SWR is about 2.0, matching the stated result.