Further comments on the design of log-periodic dipole antennas

Abstract

The design procedure for the log-periodic dipole (LPD) antenna is discussed, by extending the results presented in a previous paper by the authors. The results of gain calculations, already published, are summarized and extended to cases of very thick dipoles. The gain analysis is completed with a discussion of the optimum antenna input feed line <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z_{0}'</tex> the achievable VSWR, the voltage gradient, and the effects of the presence of the ground. All the results of calculations given here are presented as a function of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z_{0}</tex> (the characteristic impedance of the transmission line feeder), <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h/a</tex> (the ratio between the half-length and the radius of the dipoles), <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\tau</tex> (the logarithmic decrement of the geometrical configuration), and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma</tex> (the spacing ratio of dipoles), i.e., the parameters, which usually describe the geometry of an LPD array. The results of calculations are presented in many diagrams, for different values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\tau,\sigma, Z_{0}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h/a</tex> , which can be useful for accurate design of LPD antennas including those for high-power applications. Measurements of VSWR performed on antenna models have confirmed the computed results.