Log-periodic antenna: Difference between revisions
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== External links == |
== External links == |
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*[http://www.antennasoftware.com.ar/1_5_PRODUCTS.html AN-SOF Antenna Simulation Software] |
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*[http://www.changpuak.ch/electronics/lpda.php LPDA Online Calculation] |
*[http://www.changpuak.ch/electronics/lpda.php LPDA Online Calculation] |
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*[http://www.members.westnet.com.au/impeh/log%20periodic_A.htm Some thoughts on Log-Periodic Antennas] |
*[http://www.members.westnet.com.au/impeh/log%20periodic_A.htm Some thoughts on Log-Periodic Antennas] |
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Revision as of 04:42, 2 April 2012
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In telecommunication, a log-periodic antenna (LP, also known as a log-periodic array or log periodic beam antenna/aerial) is a broadband, multi-element, directional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The individual components are often dipoles, as in a log-periodic dipole array (LPDA). Log-periodic antennas are designed to be self-similar and are thus also fractal antenna arrays. The log periodic antenna was invented by Dwight E. Isbell, Raymond DuHamel and variants by Paul Mayes. 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. Lawsuits regarding the antenna patent which the UI Foundation lost, evolved into the Blonder-Tongue doctrine. This precedent governs patent litigation. [1]
It is normal to drive alternating elements with 180° (π radians) of phase shift from one another. This is normally done by connecting individual elements to alternating wires of a balanced transmission line.
The lengths and spacings of the elements of a log-periodic antenna increase logarithmically from one end to the other. A plot of the input impedance as a function of logarithm of the excitation frequency shows a periodic variation.
This antenna design is used where a wide range of frequencies is needed while still having moderate gain and directionality. It is sometimes used for a (VHF/UHF) television antenna. [1]
Popular Amateur radio variations
HB9CV
The HB9CV is a very popular two-element beam which can be considered[citation needed] as a log-periodic dipole array with only two elements. Antenna Design Details and Online HB9CV Antenna Calculator
ZL special[citation needed]
This is a beam antenna which for a given boom length gives a higher gain than a Yagi antenna, it is a log-periodic[citation needed] where only two elements are driven with a series of parasitic elements (directors) in front of the smaller of the two driven elements.
The driven elements are folded dipoles which are linked by a length of balanced twin-lead feed line. Unlike the bidirectional W8JK designs, the ZL Special is essentially a unidirectional beam[2] [3] ; the polar plots of the ZL special and the HB9CV are heart shaped (cardioid), while the typical Yagi antenna has a large forward lobe and a smaller back lobe.
History of the ZL Special
A New Zealand ham, George H. Pritchard (ZL3MH), brought the design to attention in 1949 (based on ideas of W5LHI and W0GZR), hence the "ZL" part of the name given the 3MH beam by Fred C. Judd (G2BCX), who further developed variants[4]
Sources
This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).
- ^ http://www.radio-electronics.com/info/antennas/log_p/log_periodic.php
- ^ Orr, William I. (1955). Handbook. Radio Publications, Inc. p. 156.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Schultz, John J. "A Broomhandle Beam For 10 Meters" (PDF). Retrieved 6 June 2011.
- ^ Cebik, L. B. "The Poor Old ZL Special". Retrieved 6 June 2011.