" A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional, antenna designed to operate over a wide band of frequencies. It was invented by Dwight Isbell and Raymond DuHamel at the University of Illinois in 1958.
The LPDA (log-periodic dipole array) normally consists of a series of dipoles known as "elements" positioned along a support boom lying along the antenna axis. The elements are spaced at intervals following a logarithmic function of the frequency, known as d or sigma. The length of the elements correspond to resonance at different frequencies within the antenna's overall bandwidth. This leads to a series of ever-shorter dipoles towards the "front" of the antenna. The relationship between the lengths is a function known as tau. The ever-decreasing lengths makes the LPDA look, when viewed from the top, like a triangle or arrow with the tip pointed in the direction of the peak radiation pattern. Sigma and tau are the key design elements of the LPDA design..."
A report about the construction of my first Log-Periodic Antenna (following the concept of OE3MZC) in ADL328 on 2017-06-24 will be posted here soon!