Keywords
antenna, dipole, antenna gain, effective aperture area,
link budget, radiation resistance, cage dipole, folded dipole,
balun, monopole,
biconical dipole, discone
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Abstract
Much of the work of Spectrum
Planning Group is based on well established ‘principles
of antennas and propagation’. Propagation matters
have received a lot of attention over the years and much
has been written on the topic but the ‘antennas’ part,
although arguably simpler, may lack a suitable written
reference that gathers much of the relevant material into
one place. The primary purpose of this White Paper is to
take a step towards correcting this state of affairs, but
a huge amount of underlying complexity comes to light when
one ‘scratches the surface’ of a topic like
this. A secondary objective, then, is to present some of
the more interesting and useful facts, and to provide simple,
physical explanations wherever possible.
In summary, this White Paper is intended
to provide a compendium of well-known and obscure facts
about dipole antennas and isotropic sources including
effective aperture areas, coupling factors, radiation
resistances and link budget equations. What began as
a simple case of looking up the effective aperture
area of a dipole developed into a quest for the whole
story about dipole antennas and has resulted in this
re-working of a small part of a very-old, but intriguing
story.
Of course, spectrum planning for terrestrial
broadcasting involves many more-complicated antennas
such as log-periodic dipole arrays and Yagi-Uda arrays,
not to mention the multitude of clever transmitting
antenna designs based on slots. It wouldn’t be
possible to do these justice as well in a document
of this size so I’ve deliberately limited the
scope.
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