chapter  14
17 Pages

Log-Periodic Antennas

WithBoris Levin

Log-periodic dipole antennas (LPDA) have been used widely in the past decades. Their creation represents a significant step in the development of wide-range directional antennas. PDA provides directional radiation along its longitudinal axis and retains shape of the directional pattern over a wide frequency range. They have also constant input impedance. Log-periodic antennas have rather large overall dimensions. In order to decrease transverse dimensions, it is expedient to shorten the longest dipoles using loads of different kind or structures with the slowing-down, that is, which are used for reducing the monopole's and dipole's length. The dipoles length is the same, but the helical wire length is twice as much as the straight rod's length. Linear-helical dipole in contrast to straight and helical dipole has two serial resonances, and the ratio of the resonant frequencies for the same dipole's length is equal to the slowing factor of the helical dipole.