Antennas

Half Wave Dipole

  • If a half wavelength of wire is cut at the centre and fed with RF power at the frequency at which it is resonant it is called a half wave dipole and has a feed point impedance of about 40-70Ω depending on height above ground
  • A half wave dipole is a balanced antenna and needs a balanced feed.  This can be either typically coaxial cable and a balun (balance-to-unbalance transformer) or 75 or 450Ω balanced line.  The loss due to the 6:1 mismatch (6:1 SWR) on 450Ω line is inconsequential because this type of line is very low loss, though it needs to be matched to the Tx output