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English: A wire log-periodic monopole antenna for military communication, from a US Navy training manual. It consists of many vertical wire monopole driven elements of gradually decreasing length suspended through insulators from a support line between two masts, attached in parallel to a feedline at the bottom. The log-periodic antenna, invented by Dwight E. Isbell and Raymond DuHamel in 1958, is a broadband high-gain antenna. Log-periodic dipole antennas (LPDAs) are widely used as rooftop television antennas, but vertical monopole versions like this can also be used in the MF and HF band. Each vertical element serves as a quarter-wave monopole radiator, one half of a dipole antenna. The other side of the feedline to the transmitter or receiver is attached to a buried ground system under the antenna, and the reflection of the element in the ground plane provides the other half of the dipole. The antenna radiates vertically polarized radio waves in a beam off the narrow end of the antenna. The antenna has a fairly constant gain between the wavelengths equal to 4 times the longest element and 4 times the shortest element. A typical version designed to cover a frequency range of 2-30 MHz requires a 140 ft tower and the antenna is 500 ft long. The US Navy AS-2224/FRC is a typical portable version.