Advanced Qualification · A-007 Feedlines and matching · A-007-007-002
Most simple horizontally polarized antennas do not exhibit significant directivity unless they are:
- Aa half wavelength or more above the ground
- Ban eighth of a wavelength above the ground
- Ca quarter wavelength above the ground
- Dthree-eighths of a wavelength above the ground
Correct answer: A — a half wavelength or more above the ground. From the official ISED question bank, verified word for word.
Why
When a horizontal antenna sits less than half a wavelength above the earth, the ground reflects its radio waves in a way that cancels out forward and backward signals, leaving the antenna to radiate almost equally in all directions. The full explanation — and one for every question — is in Pro.
Practise this section
Feedlines and matching is section A-007 of the Advanced exam: Feedlines and matching at the advanced level: transmission line theory, impedance transformation, stubs and matching networks.
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