VSWR is a measure of impedance mismatch on a line; it is given by which expression and is measured with which tools?

• A. It measures impedance mismatch and equals (1+|Γ|)/(1-|Γ|); measured with SWR meter or VNA
• B. It measures voltage amplitude only
• C. It measures current
• D. It measures average power

Answer: (A)

Understanding VSWR starts with how a wave on a transmission line interacts with the load. When the load isn’t equal to the line’s characteristic impedance, part of the incident wave is reflected, creating standing waves. VSWR measures how severe that mismatch is by comparing the maximum and minimum voltages along the line, which is directly tied to how much of the wave is reflected.

The key relation is VSWR = (1 + |Γ|) / (1 − |Γ|), where Γ is the reflection coefficient given by Γ = (ZL − Z0) / (ZL + Z0). This shows how the strength of the reflected wave (encoded in |Γ|) translates into the standing-wave ratio. If the load matches perfectly (Γ = 0), VSWR is 1, indicating no standing waves. As the mismatch grows (Γ approaches 1 in magnitude), VSWR increases toward infinity.

VSWR is measured with an SWR meter, which directly reads the ratio of forward to reflected power, or with a vector network analyzer (VNA), which can measure the reflection coefficient (or impedance) and from that derive VSWR. The other options don’t describe what VSWR quantifies or how it’s measured, since VSWR is about impedance mismatch and standing-wave formation, not mere voltage amplitude, current, or average power.