Which of the following describes a log-periodic antenna?

A log-periodic antenna is a multi-element directional antenna designed to operate over a wide band of frequencies. It achieves this wideband capability by varying the physical length of the driven elements and the spacing between them in a logarithmic progression along the boom. This design ensures that as the operating frequency changes, a different active region (set of elements) becomes electrically resonant. This allows the antenna to maintain a relatively constant gain and impedance across its entire operating range. Distractors involving impedance or gain varying logarithmically are incorrect; the goal of the design is actually to keep those electrical characteristics constant while the physical structure varies.