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Directional antenna. A multi-element, log-periodic dipole array. A 70-meter Cassegrain radio antenna at GDSCC, California. Patch antenna gain pattern. A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater ...
A beam waveguide antenna is a particular type of antenna dish, at which waveguides are used to transmit the radio beam between the large steerable dish and the equipment for reception or transmission, like e.g. RF power amplifiers. 34-meter beam waveguide antenna at NASA's Deep Space Communications Complex site outside Madrid, Spain, part of ...
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.
Aperture blockage – In front-fed parabolic dishes where the feed antenna is located in front of the dish in the beam path (and in Cassegrain and Gregorian designs as well), the feed structure and its supports block some of the beam. In small dishes such as home satellite dishes, where the size of the feed structure is comparable with the size ...
Directivity. In electromagnetics, directivity is a parameter of an antenna or optical system which measures the degree to which the radiation emitted is concentrated in a single direction. It is the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. [1] Therefore, the ...
Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. [1] This is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference.
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 ...
a passive element slightly longer than and located behind a radiating dipole element that absorbs and re-radiates the signal in a directional way as in a Yagi antenna array. a flat reflector such as used in a Short backfire antenna or Sector antenna. a corner reflector used in UHF television antennas. a cylindrical reflector as used in Cantenna.