Question concerning polarisation

[JamesGoh]

In a textbook on wireless communications that I am reading, the author states that transmissions from a vertically polarised antenna will undergo interactions which would cause energy to leak into the orthogonal polarisation component (Im assuming the H-field of an EM wave) before reaching the receiver (and vice versa).

My question is, what kind of scenarios in the physical world are likely to cause a vertically polarised antenna to leak energy into the horizontal polarisation component. Likewise, what would cause a horizontally polarised antenna to emit energy into it vertical polarisation component ?

thanks

 

[Andy Resnick]

Any scattering process (e.g. from buildings), where the incident polarization state can then be decomposed into an s- and p-polarized state.

 

[Bob S]

Faraday rotation of radio waves in the ionosphere, combined with the Earth's magnetic field, can rotate the polarization of a radio wave.