Comments on the design of log-periodic dipole antennas

Abstract

The design procedure of the log-periodic dipole (LPD) antennas is discussed. The results of the calculations carried out by the use of the more recent and accurate methods of the analysis for the arrays of unequal dipoles, are compared with those already available in the literature. The calculations refer to the gain of LPD antenna as a function of Z_{0} , the characteristic impedance of the exciting transmission line, of h/a , the ratio between the half-length and the radius of dipoles, of \tau and \sigma , two parameters which describe the geometry of the LPD antenna. The values of gain are lower than those given by earlier calculations. The degradation of the gain is more consistent, when the values either of Z_{0} or h/a are increased with respect to Z_{0} = 100 \Omega and h/a = 125 , which are parameters often used in the literature. The many diagrams included in this paper for different values of \tau, \sigma, Z_{0} , and h/a can be useful in a more accurate design of an LPD antenna. Confirmation of the computer data has been obtained by the tests performed on various scale models and on a full scale antenna.