This paper is concerned with the problem of maintaining a low standing wave, over a wide frequency band, on the feeders of an aerial system. The problem involves a study of typical aerial impedance variations with frequency and of the possible devices which can be used to compensate these variations. The paper is illustrated by experimental impedance measurements on balanced twin feeders in the 500–600 Mc/s band. The results quoted give the authors considerable confidence in their methods of impedance measurement and compensation.