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antenna
- (physics) A device for collecting (receiving) or transmitting (radiating) radio signals, the design of which depends on the wavelength and amplitude of the signals. In essence a transmitting antenna is a combination of conductors which converts AC (alternating current) electrical energy into radio waves. The simple dipole consists of two straight conductors aligned end on and energized at the small gap which separates them. The length of the dipole determines the frequency for which this configuration is most efficient. It can be made directional by adding electrically isolated director and reflector conductors in front and behind. Other configurations include the folded dipole, the highly-directional loop antenna, and the dish type use for microwave links. Receiving antenna can consist merely of a short dielectric rod or a length of wire for low-frequency signals. For VHF and microwave signals, complex antenna configurations similar to those used for transmission must be used. See also radio telescope.
• RADIO ASTRONOMY AND COMMUNICATIONS - (zoology) Usually one of a pair of many-jointed, whip-like structures present on the head of many arthropods, particularly insects (first appendage on head) and crustaceans(second appendage). Antennae have a sensory function, though in some crustaceans they are used for attachment or swimming.
• ZOOLOGY
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