10.2.4 Baluns

A balun (a contraction of balanced-to-unbalanced) is a device used to connect a balanced transmission line to an unbalanced one while maintaining proper impedance transformation and preventing unwanted common-mode currents. Baluns are commonly used to connect balanced antennas, such as dipoles, to unbalanced coaxial feed lines.

Baluns may be implemented using transformer coupling, transmission-line sections, ferrite cores, or quarter-wave impedance transformers. In addition to impedance matching, an effective balun suppresses common-mode currents on the outer conductor of coaxial cables, thereby reducing radiation, pattern distortion, and electromagnetic interference. Proper balun selection is essential in antenna systems to preserve symmetry and ensure accurate radiation characteristics.