Which characteristic is typical of a semi-directional antenna such as the ones listed?

Which characteristic is typical of a semi-directional antenna such as the ones listed?

• A. Yagi (a semi-directional antenna).
• B. Omnidirectional vertical.
• C. Dipole with no directionality.
• D. Isotropic radiator.

Answer: (A)

Semi-directional antennas focus energy toward a specific direction while still emitting some radiation in other directions. A Yagi fits this description because it uses multiple elements (driven, reflector, and directors) to shape the pattern into a clear front lobe with higher forward gain and a narrower beam. This creates a defined direction to point toward a target, with less radiation off to the sides and rear. An omnidirectional vertical radiates more or less the same in all horizontal directions, so it lacks a focused beam. A bare dipole does have directionality, but its pattern is a basic figure‑eight and isn’t the classic semi-directional behavior emphasized by a Yagi. An isotropic radiator is a theoretical reference that would radiate equally in all directions with no preferred beam.

Semi-directional antennas focus energy toward a specific direction while still emitting some radiation in other directions. A Yagi fits this description because it uses multiple elements (driven, reflector, and directors) to shape the pattern into a clear front lobe with higher forward gain and a narrower beam. This creates a defined direction to point toward a target, with less radiation off to the sides and rear.

An omnidirectional vertical radiates more or less the same in all horizontal directions, so it lacks a focused beam. A bare dipole does have directionality, but its pattern is a basic figure‑eight and isn’t the classic semi-directional behavior emphasized by a Yagi. An isotropic radiator is a theoretical reference that would radiate equally in all directions with no preferred beam.