General exam question G9A07
Subelement G9, ANTENNAS AND FEED LINES· Group G9A
What must be done to prevent standing waves on a feed line connected to an antenna?
- A.The antenna feed point must be at DC ground potential
- B.The feed line must be an odd number of electrical quarter wavelengths long
- C.The feed line must be an even number of physical half wavelengths long
- D.The antenna feed point impedance must be matched to the characteristic impedance of the feed line (correct answer)
WhyPreventing standing waves on a feed line connected to an antenna requires the antenna feed point impedance to be matched to the characteristic impedance of the feed line. Standing waves on a feed line arise from a mismatch between the line's characteristic impedance and whatever impedance is connected at its far end, so eliminating them means making the antenna feed point's impedance match the feed line's characteristic impedance, answer D. Grounding the feed point at DC, or picking a particular electrical line length, doesn't fix an underlying impedance mismatch, a mismatched line produces standing waves at any length, so A, B, and C are wrong.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2023-2027 NCVEC Element 3 pool (public domain); the explanation above is original writing, see our methodology.
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