Log-periodic antenna

Electrically, it simulates a series of two- or three-element Yagi–Uda antennas connected together, each set tuned to a different frequency.

[1][2] The radiation pattern of the antenna is unidirectional, with the main lobe along the axis of the boom, off the end with the shortest elements.

A parallel wire transmission line usually runs along the central boom, and each successive element is connected in opposite phase to it.

[4] The Yagi and the LPDA designs look very similar at first glance, as they both consist of a number of dipole elements mounted along a support boom.

However, the system is somewhat more complex than that, and all the elements contribute to some degree, so the gain for any given frequency is higher than a Yagi of the same dimensions as any one section of the log-periodic.

In its use as a television antenna, it was common to combine a log-periodic design for VHF with a Yagi for UHF, with both halves being roughly equal in size.

Y. Mushiake found, for what he termed "the simplest self-complementary planar antenna," a driving point impedance of η0/2=188.4 Ω at frequencies well within its bandwidth limits.

[10][11][12] John Dunlavy invented the log-periodic antenna in 1952 while working for the United States Air Force but was not credited with it due to its "Secret" classification.

[13] The University of Illinois at Urbana–Champaign had patented the Isbell and Mayes–Carrel antennas and licensed the design as a package exclusively to JFD Electronics in New York.

Channel Master and Blonder Tongue Labs ignored the patents and produced a wide range of antennas based on that design.