File:Antenna UHF 01.JPG
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Français : L'antenne ground plane UHF 450 MHz à 470 MHz ou GPA (Ground Plane Antenna) est un dipôle dans lequel on a remplacé la moitié par un « plan de sol », la moitié conservée étant normale à cette surface. Si le plan de sol est suffisamment grand, le demi-dipôle se comporte exactement comme un dipôle entier (type: dipôle demi-onde λ/2) car sa réflexion dans le plan de sol forme la partie manquante. La longueur physique est environ égale au quart de la longueur d'onde de la fréquence sur laquelle l'antenne est accordée. Ces brins, disposés en cercle inclinés vers le bas ; en nombre de 3, ils constituent une surface conductrice de l'électricité, même si cette surface n'est pas parfaite pour être alimenté par un câble coaxial de 50 ohms .
English: A UHF ground plane antenna for 450 MHz to 470 MHz. The vertical whip is approximately one quarter of the wavelength of the radio waves, and functions as a quarter-wave en:monopole antenna. The three downward pointing quarter wave whips extending from the base of the vertical function as a ground plane for the monopole. They create an electrical "image" of the top whip, on the other side of the ground plane. The two antennas, the monopole and its image, are together equivalent to a half-wave dipole antenna so the radiation pattern of the ground plane antenna is the same as the top half of the pattern of the half wave dipole: It is omnidirectional, radiating maximum power in horizontal directions, with the power declining with elevation angle to zero on the antenna's axis. The maximum gain is twice (3 dB more than) that of a half wave dipole's 2.19 dBi, or 5.19 dBi. If the ground plane wires extended out horizontally from the base of the monopole the impedance would be half that of the dipole, or 36.5 ohms. However the downward slant of the ground plane wires serves to increase the antenna impedance, so the antenna is a good match for the 50 ohm coaxial cable feedline. |
| Date | |
| Source | Own work |
| Author | F1jmm |
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I, the copyright holder of this work, release this work into the public domain. This applies worldwide. In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law. |
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This is a retouched picture, which means that it has been digitally altered from its original version. Modifications: picture manager bright. Modifications made by F1jmm.
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| current | 04:29, 10 October 2012 | | 680 × 1,170 (463 KB) | F1jmm (talk | contribs) | User created page with UploadWizard |
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