Question
What must be done to prevent standing waves on a feed line connected to an antenna?
Answer Options
- 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: D
Explanation
Standing waves are the result of reflected power caused by an impedance mismatch between the feed line and the antenna. To prevent standing waves, all of the power sent down the line must be absorbed by the antenna at the end of the line.
This is achieved when the antenna feed point impedance must be matched to the characteristic impedance of the feed line. For example, if a 50 \text{ ohm} coaxial cable is used, the antenna must present a 50 \text{ ohm} resistive load at its feed point to achieve a perfect 1:1 Standing Wave Ratio (SWR) and eliminate reflections.
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