Which statement best describes a half-wave dipole compared with a full-wave dipole?

• A. A half-wave dipole is resonant at λ/2 with about 73-ohm feed impedance in free space; a full-wave dipole is λ long with higher impedance.
• B. A half-wave dipole has higher impedance than a full-wave dipole.
• C. A half-wave dipole resonates at λ; a full-wave resonates at λ/2.
• D. Half-wave and full-wave dipoles have identical radiation patterns.

Answer: (A)

Resonance in a center‑fed straight dipole happens most cleanly when the length is about half a wavelength. At that λ/2 length, the current is strongest at the middle and falls to zero at the ends, giving a simple, efficient radiating system. In free space this configuration typically presents a feedpoint impedance around 73 ohms, which is a familiar match for common 50-ohm coax.

When you extend the dipole to a full wavelength, the current distribution changes to accommodate two half-wavelength sections along the wire. This changes the electromagnetic loading at the feedpoint, so the impedance goes up compared with the half-wavelength case. The result is a higher feed impedance for the λ-long dipole.

The statements about resonance and impedance in this way align with how length controls the standing wave pattern and the resulting feedpoint impedance. The other ideas—such as the half-wave resonating at λ or the full-wave at λ/2, or having identical radiation patterns—don’t match the way current distribution and impedance actually behave for these two lengths.