R&D Report 1970-31 : VHF receiving aerials: The use of active elements D.J. Whythe An array of half-wavelength dipoles forms the most convenient type of aerial for VHF television re-broadcast reception. The principles are well-known by which such an array can be designed to have any specified directivity but re-radiation from the dipole makes it difficult to implement those principles in practice. This report shows that the difficulty can be overcome by incorporating an amplifier directly across the terminals of each dipole such that the dipoles operate under substantially open-circuit conditions. A suitable design for a practical active dipole is described and, as an example, the directivity that could be achieved using an array of eight such dipoles is given.