• Pays
• Europe

• Fabricant / Marque
• Homebrew - ORIGINAL, Europe others

• Année
• 1976

• Catégorie
• Antenne ou coupleur

• Radiomuseum.org ID
• 306039

Cliquez sur la vignette du schéma pour le demander en tant que document gratuit.

• Gammes d'ondes
• Bandes en notes

• Haut-parleur
• - - Pas de sortie basse fréquence

• Matière
• Matériaux divers

• De Radiomuseum.org
• Modèle: 37-element UHF antenna - Homebrew - ORIGINAL, Europe

• Forme
• Formes diverses décrites en notes

• Dimensions (LHP)
• 730 x 750 x 3660 mm / 28.7 x 29.5 x 144.1 inch

• Remarques

• This 37-element 412 MHz antenna was designed by Bruce Taylor. First the phase velocity characteristics of uniform periodic rod structures of 6.35 mm diameter elements of length 27 cm and 30 cm were measured for a range of spacings, using a long boom carrying a reflector at one end and a feed dipole at the other. The standing wave pattern is measured over several nodes towards the reflector end, where the surface wave is well established. The fields of the higher spatial harmonics attenuate rapidly in the direction transverse to the boom, so that when the measurement probe is moved at some distance from the tips of the elements it detects primarily the field of the fundamental Hartree component.

  In the main body region extending over 75% of the antenna length the mean value of λ_c/λ_z = 1.06 to optimise the gain. A phase velocity taper of 5% is then applied to this region to reduce the amplitude of the first sidelobes and broaden the bandwidth at the cost of a negligible reduction in gain. For maximum coupling between the surface wave on the structure and the feed, a value of λ_c/λ_z > 1.2 is achieved by progressively diminishing the phase velocity in a feed taper region extending over 20% of the length of the antenna. Finally, over the 5% of antenna length remote from the feed, a terminal taper is created by increased director spacing to match the free space wave to the surface wave with minimum reflection. The phase velocity tapering is achieved by progressively altering the spacing of the directors, rather than their length.

  The angle between each half-plane of the grid reflector and the boom can be adjusted, as also the distance of the reflector from the feed. For a reflector/feed spacing of about λ/4 the effect of these adjustments on the antenna gain is not critical, so that they can be altered to optimise the impedance matching.

  The full-wave dipole feed has broader bandwidth than a folded λ/2 dipole and a double delta-loop. Production of the plane reflector is more economical than that of the angled type required by the folded dipole, while the feed itself is more easily fabricated than the double delta-loop.

  Forward gain 18 dB.
  Front/back ratio 30 dB.
  Feed impedance 50 ohms.
  Beamwidth 27 degrees.
  First-order sidelobes 18 dB down at ±35º.
  Centre frequency 412 MHz.
  Bandwidth (3 dB) 374 - 454 MHz, flat (0.1 dB) 402 - 424 MHz.

  Dimensions in cm:

  Reflector
  Planar grid type on 2.54 x 2.54 x 75 central support.
  No. of elements 9.
  Element diameter 0.953, length 73, spacing 8.0.
  Reflector/feed spacing 18.2.

  Feed
  Full-wave planar 2-element fan-type dipole centre-fed by 4:1 impedance transformer/balun.
  Element diameter 0.635, length (overall) 69.5.
  Fan separation angle 30º.
  Balun length (0.67 velocity factor coaxial) 24.4.

  Slow-wave structure
  Boom 2.54 x 5.08 x 366 (2.54 dimension in director plane).
  No. of directors 35, diameter 0.635.
  Director lengths (numbered consecutively from the feed):
  Director 1:  33
  Director 2:  32.5
  Director 3:  32
  Director 4:  31
  Director 5:  30
  Director 6:  29
  Director 7:  28
  Directors 8 - 35:  27

  Element spacings (Feed - Director 1 - Director 2 - ... - Director 35)
  6.2  6.2  6.2  6.3  6.3  6.4  7.0  8.0  8.6  8.8  9.0  9.1  9.2  9.4  9.5  9.6  9.7  9.9  10.0  10.1  10.2  10.4  10.6  10.8  11.0  11.1  11.4  11.7  12.1  12.2  12.6  12.8  13.0  13.5  17.5

• Auteur
• Modèle crée par Bruce Taylor. Voir les propositions de modification pour les contributeurs supplémentaires.

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