In a Yagi-Uda antenna, what are the roles of a director and a reflector, and how do they influence forward gain?

• A. Directors focus energy to increase forward gain; reflector is slightly longer and helps directivity by rear suppression
• B. Directors increase impedance; reflector decreases bandwidth
• C. Directors decrease forward gain; reflector increases side lobes
• D. Directors have no effect on gain

Answer: (A)

Parasitic elements in a Yagi-Uda antenna shape the radiation pattern to boost forward gain. The driven element is the one actually fed with RF power. The director, which is shorter than the driven element and placed in front of it, is excited by the field from the driven element and tends to cause radiation to reinforce in the forward direction. This constructive interaction narrows the beam and increases the amount of energy steered toward the forward side, raising the forward gain.

The reflector sits behind the driven element and is slightly longer. Its role is to reflect energy back toward the forward direction while suppressing rearward radiation, which further enhances the forward-directed pattern and improves the front-to-back ratio. So together, the director and reflector direct energy into a stronger, more concentrated forward beam.

Other statements don’t capture this primary behavior: the director’s main job isn’t to increase impedance or to affect bandwidth in the stated way, and saying the director has no effect on gain ignores how these parasitic elements actively shape the pattern.