====== Antenna ======

An antenna couples a radio signal to the space around it. Its behaviour depends on frequency, geometry, installation height and nearby objects. A [[transmission_line|feed line]] carries energy between the radio and antenna.

===== Common antenna families =====

  * **Dipole:** a balanced antenna with two conducting sections, often used as a practical starting point for HF.
  * **Vertical:** useful where space and installation constraints favour a vertical structure; the return-current path is part of the design.
  * **Directional antenna:** concentrates radiation in selected directions. A Yagi is a familiar example.
  * **Loop:** a closed conducting path, with many possible sizes and designs.

No antenna is best for every station. Available space, bands, mounting options and the intended paths help determine a suitable design.

===== Feed lines and matching =====

Coaxial cable is widely used because its shielding and routing are convenient. Balanced lines are another option. Loss, impedance, weather protection and connector quality all affect the complete system.

[[standing_wave_ratio|Standing wave ratio (SWR)]] describes mismatch along a transmission line. A low SWR is useful, but it does not by itself prove that an antenna radiates efficiently. A dummy load can present a good match while intentionally converting most transmitted energy to heat.

===== Documenting an installation =====

Include a diagram, dimensions, feed-line type and length, installation height, measurement method and operating conditions. Keep measured results separate from predictions and simulations.

See [[wiki:article_template|the article template]] for a consistent way to document a design.