Broadband logarithmically periodic antenna structures

Antenna structures for which the input impedance and radiation patterns vary periodically with the logarithm of the frequency are described. For a particular class of these structures the variation of the electrical characteristics over a period is negligible, the result being an antenna for which the impedance and patterns are essentially independent of frequency over bandwidths greater than ten to one. The antennas are linearly polarised and bi-directional beams of approximately equal principal plane beamwidths are obtained. The beamwidth may be controlled to a considerable extent by the geometry of the structure.