A dipole antenna is one of the simplest and most widely used types of radio antenna. It consists of two conductive elements—usually rods or wires—arranged end to end with a feed point at their junction. The most common form is the half-wave dipole, whose overall length is approximately one half of the wavelength of the operating frequency; at resonance the antenna efficiently radiates or receives electromagnetic waves and typically produces a figure‑eight radiation pattern in free space.

Key characteristics include the center feed point where the transmission line connects, the current distribution that peaks at the feed and tapers toward the ends, and a linear polarization determined by the element orientation. A resonant half‑wave dipole in free space has a characteristic input impedance on the order of tens of ohms (commonly cited near 73 Ω), though real installations and nearby objects change this value. Bandwidth is moderate but can be increased by element thickness or by using multiband variants.

Construction and common variants

  • Center‑fed half‑wave dipole — the canonical form used as a reference in antenna theory.
  • Folded dipole — two parallel conductors joined at their ends, offering higher input impedance and broader bandwidth.
  • Off‑center fed dipole (OCFD) — tapped away from the center to provide multiple resonances or better match to feedlines.
  • Monopole — a single element over a ground plane, electrically equivalent to a dipole with the ground as a mirror.

The dipole often appears as the driven element in more complex systems: for example a Yagi‑Uda array uses a dipole as the active radiator, and many simple television and FM broadcast antennas are based on dipole sections. Detailed descriptions and practical guides can be found in general antenna references and online resources such as basic dipole tutorials and studies of the radiation pattern. Designers also consult compilations of antenna designs that use dipoles as building blocks.

Historically, early radio experimenters used dipole‑like conductors to demonstrate electromagnetic waves. Over time the dipole became a standard teaching example because it embodies many core antenna principles—resonance, current distribution, impedance, polarization and pattern shape—while remaining simple enough for practical construction and measurement.

In practice, users must consider feedline matching (often via a balun when feeding with an unbalanced coaxial cable), mounting height and surrounding objects, which affect gain and pattern. Compared to a monopole, the dipole does not require a ground plane, but installation details determine its real‑world performance. Because of its simplicity and predictable behavior the dipole remains a foundational element in both theoretical study and practical antenna engineering.