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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 John Dunlavy in 1952. The most common form of log-periodic antenna is the log-periodic dipole array or LPDA, The LPDA consists of a number of half ...
The "Log-Periodic Dipole Array" [17] or "Log-Periodic Dipole Antenna" [18] (LPDA), is a practically modified self-complementary antenna. LPDA has transposed excitation [ 19 ] for the dipole array resulted from folding up [ 20 ] the antenna structure to obtain unidirectional radiation, that is inevitable outcome of the modification.
A modern high-gain UHF Yagi television antenna with 17 directors, and one reflector (made of four rods) shaped as a corner reflector. Drawing of Yagi–Uda VHF television antenna from 1954, used for analog channels 2–4, 54–72 MHz (U.S. channels). It has five elements: three directors (to left) one reflector (to right) and a driven element ...
Antennas can be classified in various ways, and various writers organize the different aspects of antennas with different priorities, depending on whether their text is most focused on specific frequency bands; or antenna size, construction, and placement feasibility; or explicating principles of radio theory and engineering that underlie, guide, and constrain antenna design.
Antenna measurement techniques refers to the testing of antennas to ensure that the antenna meets specifications or simply to characterize it. Typical parameters of antennas are gain, bandwidth, radiation pattern, beamwidth, polarization, and impedance. The antenna pattern is the response of the antenna to a plane wave incident from a given ...
For such an antenna, the near field is the region within a radius r ≪ λ, while the far-field is the region for which r ≫ 2 λ. The transition zone is the region between r = λ and r = 2 λ . The length of the antenna, D, is not important, and the approximation is the same for all shorter antennas (sometimes idealized as so-called point ...
Intermediate-field region. In antenna theory, intermediate-field region (also known as intermediate field, intermediate zone or transition zone) refers to the transition region lying between the near-field region and the far-field region in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse ...
[3] [dubious – discuss]) This was one of the investigations that led to the victory of the wave theory of light over then predominant corpuscular theory. In antenna theory and engineering, the reformulation of the Huygens–Fresnel principle for radiating current sources is known as surface equivalence principle. [7] [8]