"Szczepan Bia³ek" wrote in message
...

"christofire" wrote
...


Now I understand what you meant by 'total field' - sum of powers of
components in all polarisations.

Does one wave has many polarizations, or one antenna has many
polarizations? Which one: transmitter or receiver? Could you teach me?
A*


You appear to have changed your identity from S* to A* !

The answers according to the physics that real-life radio communication
depends upon, and was designed by, a

A single EM wave is plane polarised. It is composed of a magnetic field H
that acts in a direction perpendicular to the direction of propagation, the
magnitude and sign of this field varying as a travelling wave in the
direction of propagation, and an attendant electric field E that also acts
in a direction perpendicular to the direction of propagation. The magnitude
and sign of the electric field varies as a travelling wave, coherent and in
phase with the magnetic field and the magnetic field is a direct consequence
of current flowing in the transmitting antenna. The directions in which the
H and E fields act, in the plane transverse to the direction of propagation,
are mutually perpendicular and the direction in which the E field acts, by
convention, defines the polarisation.

Thus a single EM wave has a single, plane, polarisation. Different
combinations of waves are possible such as circular polarisation and, more
generally, elliptical polarisation, but these can always be resolved into
orthogonal plane components.

Simple antennas like straight-wire dipoles and loops transmit and respond to
plane polarised EM waves. More complicated antennas can be made to transmit
and receive circular polarisation of one sense or the other, and generally
an antenna will tend to transmit or be sensitive to some combination of
different plane polarisations. In addition to radiated EM waves, there are
also induction fields in a region close to the antenna.

In a system that contains no anisotropic material (e.g. magnetised ferrite),
when the distance between transmitting and receiving antennas is at least
tens of wavelengths, the principle of reciprocity applies. By this
principle the properties of an antenna when transmitting are the same as
when it is receiving - the properties including the polarisation, radiation
pattern and terminal impedance.

If you find any of this interesting, please don't believe what I've written
here but go to a technical library (e.g. at a University) and look up the
authoritative sources - books on antennas and propagation by Kraus, Jasik,
Jordan and Balmain, Terman, etc.

Please _do not_ respond here telling me or the group that EM waves are
longitudinal and are not polarised.

Chris