"Szczepan Bia³ek" wrote in message
...

"Dave Platt" wrote
...
In article ,
Jeff Liebermann wrote:

I forgot to connect my comments to the original question. Sorry(tm).
You're correct. There's no way to get a good isotropic radiator
pattern with a simple vertical radiator. However, you can still get
fairly close if you make the antenna sufficiently small relative to
the operating wavelength. As the physical antenna size approaches a
point radiator, the pattern starts to look rather spherical.

The difference in pattern between a half-wavelength dipole,
and an infinitesimally-short dipole (i.e. one whose length
approaches a point source) is actually quite small.

A dipole is always the two monopoles and never a point source. Only
monopole is a point source.
S*

Nonsense. Only a point can be a point source.

The principle of the infinitesimal electric doublet is the hypothetical
result of making the lengths of the elements of a balanced dipole
vanishingly small. This is useful to quantify the characteristics of the
limiting case but, because of its inherent axial symmetry, it still has the
form of a dipole and the same kind of radiation pattern with linear
polarisation and no radiation in the directions aligned with the ends of the
dipole (for the reason I gave earlier in this thread).

Monopole antennas are developed from dipoles by substituting one of the
elements, often using a 'reflection' of the remaining element in a ground
plane. Their characteristics are different from those of the parent dipole
because of this substitution but they still have the same kind of
axially-symmetric radiation pattern, with linear polarisation and no
radiation in the direction of the end of the monopole.

A point source is a hypothetical 'device' that radiates equally in all
directions. Obviously this could not be realised using a monopole because
that would provide the wrong radiation pattern.

A polarisation can be assigned to a point source, for the sake of comparison
with real antennas (which is how the point source is used), just as a point
source can be considered as transmitting or receiving a signal - but that
doesn't mean a physical antenna can be made that has the same
characteristics, that can be made to transmit or receive.

Chris