Application of the Brillouin Diagram in Log-Periodic Antenna Design

The utility of a Brillouin diagram for the design of a unit-cell and its translation to a log-periodic antenna from a uniform periodic (UP) array structure are discussed. Ten element UP array configurations of monopoles, folded monopoles (FM), folded inductively loaded monopoles (FILM), and folded normal mode helices (FNMH) are studied and the observations from said diagrams are utilized to determine critical parameters for achieving consistent backward radiation. The simulations show that initial configurations of FM and FILM log-periodic antennas without detailed parametric or optimization studies for a growth rate of 0.85 achieve VSWR < 2.5, expected radiation pattern, and acceptable front-to-back ratios over a large part of the HF band.