"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

"christofire" wrote
...

"Szczepan Bia³ek" wrote in message
...


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.

Yes. Monopole made of wire is not a point source. For this reason inventors
mounted something lake a ball on the end.

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).

Each todays dipole consist of the two monopoles in opposite phase.
There are the two seperate sources. They produce the two spherical waves.
You say they are polarised - I that they are coupled.

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.

Equipment is polarized - not waves. Point sorce cannot be polarised. The two
monopoles are always polarized. Long wire without big tip is
pseudo-polarized.
S*