Log-Periodic

Log-Periodic

A somewhat novel, but very useful, design is the log-periodic antenna. This antenna is based on the dipole element. As shown in the illustration of figure 18, it is in fact comprised of a set of dipoles, all active, that vary in size from smallest at the front to largest at the rear. Usually, this antenna is constructed so the antenna terminals are located at the front (on the shortest dipole). Figure 19 shows a typical installation. The key features of this antenna are, first of all, its broadband nature, and second, its relatively high front-to-back gain ratio. The latter feature is evident in the typical radiation pattern shown in figure 20.

Figure 18. A log-periodic antenna

Figure 19. A typical log-periodic antenna

Figure 20. A log-periodic antenna horizontal-plane pattern