SWR is defined as which of the following?

• A. SWR is the impedance of the antenna at resonance.
• B. SWR is the ratio of input power to output power of the transmitter.
• C. SWR is the ambient environmental radio noise level.
• D. SWR is the ratio of forward to reflected power on the feedline.

Answer: (D)

SWR measures how well the feedline and antenna are matched by looking at how much power is actually sent toward the antenna versus how much is reflected back toward the transmitter. Forward power travels toward the antenna, while reflected power comes back when the antenna doesn’t present the line’s characteristic impedance. If the match is perfect, almost no power is reflected and the SWR is 1:1. If there’s a mismatch, reflected power increases and the SWR rises, potentially toward very high values if the reflection is large (open or short circuit at the end).

That’s why the best description is the ratio of forward power to reflected power on the feedline. The other options describe related concepts (impedance at resonance, overall transmitter power, or ambient noise) but they do not define SWR.