Discussion
Consider a transmission line of characteristic impedance 50 ohm. Let it be terminated at one end by + j50 ohm. The VSWR produced by it in the transmission line will be :
Answer: C
The VSWR is infinity.
The reflection coefficient at the load is
\[ \begin{aligned} \Gamma &= \frac{Z_{L} - Z_{0}}{Z_{L} + Z_{0}} \\ &= \frac{j50 - 50}{j50 + 50} \end{aligned} \]
The numerator and denominator have the same magnitude, \(50\sqrt{2}\), so \(|\Gamma| = 1\). This is true of any purely reactive load: it cannot absorb power, so everything is reflected. Then
\[ \begin{aligned} \text{VSWR} &= \frac{1 + |\Gamma|}{1 - |\Gamma|} \\ &= \frac{2}{0} \to \infty \end{aligned} \]
A VSWR of 1 would need a matched 50 ohm resistive load. VSWR is a real ratio of at least 1, so 0 and +j are not possible values.
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