Abstract: A coaxial line has a conductive surrounding shield connected from a first to a second point thereon. The outer conductor of the coaxial line shield is discontinuous at an intermediate point inside the shield so that it has two intermediate ends or terminals therein. A radio frequency signal applied to one end of the electrically unbalanced coaxial line will be supplied on the balanced intermediate terminals through a broadband transformation by the coaxial line with its shield, which constitutes a balun (balancing transformer). The length of each part of the coaxial line, from each intermediate terminal to the first and second points, is preferably one-quarter wavelength at the center frequency of an applied frequency band.The coaxial line may be used with another coaxial line mounted orthogonally to the first line, with both lines mounted within a common enclosure or shield, thereby to provide a dual balun.