Kvartbølge monopolantenne
En kvartbølge monopolantenne eller kvartbølge antenne er i korte træk en radioantenne hvis ene (typisk øverst) antennefødedel er 1/4 bølgelængde lang – faktisk en halv halvbølge dipolantenne. Den anden fødedels halvdel er typisk elektrisk ledende jord – eller et kunstigt jordplan (eng. groundplane) bestående af – radialer; eksempelvis 3 eller flere elektrisk ledende (metal)stave eller rør – eller en elektrisk ledende (metal)plade.
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Crystal128-tv.svg
Forfatter/Opretter: Everaldo Coelho (YellowIcon);, Licens: LGPL
Et ikon fra Crystal-temaet
Forfatter/Opretter: Everaldo Coelho (YellowIcon);, Licens: LGPL
Et ikon fra Crystal-temaet
Antenne gp vhf 2.jpg
Forfatter/Opretter: F1jmm, Licens: CC BY-SA 3.0
VHF ground plane antenna. This is a quarter-wave whip (monopole) antenna (white rod at top) with three grounded quarter-wave conductors projecting down from the base of the whip to form a "ground plane". Ground plane antennas have an omnidirectional radiation pattern, radiating equal signal strength in all azimuthal directions, with the radiated power maximum in a horizontal direction and decreasing with elevation angle to zero on the antenna axis. The ground conductors serve to increase radiated power in the horizontal direction to twice the gain of a dipole, or 5.19 dB. 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.
Forfatter/Opretter: F1jmm, Licens: CC BY-SA 3.0
VHF ground plane antenna. This is a quarter-wave whip (monopole) antenna (white rod at top) with three grounded quarter-wave conductors projecting down from the base of the whip to form a "ground plane". Ground plane antennas have an omnidirectional radiation pattern, radiating equal signal strength in all azimuthal directions, with the radiated power maximum in a horizontal direction and decreasing with elevation angle to zero on the antenna axis. The ground conductors serve to increase radiated power in the horizontal direction to twice the gain of a dipole, or 5.19 dB. 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.