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I've just been asked a strange question that I cannot find an answer to (even on the internet it seems I can't find any explanation for this) and I ended up wondering why most of the antennas which work as "base stations" are nowadays +/- 45° polarized. While I do understand the meaning of polarization diversity, it is still not clear to me why antennas' producers chose those 2 polarizations instead of horizontal / vertical or other 2 orthogonal angles whatsoever. Moreover, I am sure that the radiators inside an antenna cannot perfectly have a +/- 45° polarization. What happens then if those are "rotated" a little bit (let's say +55° / - 35°)? Is the orthogonality the only important thing, or is a correct orientation (+/- 45°) important too and why is that?

Bonus question: I think that the polarization of mobile phones has nothing to do with the polarization of base station antennas (because of reflections and multi-paths their transmissions' polarizations could be received "rotated" in comparison to how it was sent), is that a correct assumption?

EDIT: I can't really remember the source, but I read somewhere that we don't use H-Pol, because the ground greatly attenuates the field in that case.

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  • $\begingroup$ As for polarization and reflection: Yes, multi-path reflections blur linear polarization (circular polarization is more stable, and is sometimes used to allow two channels on the same carrier frequency, but as far as I know mainly for systems in the direct line of sight as microwave point-to-point transmission). $\endgroup$ – Sebastian Riese Jul 16 '15 at 8:02
  • $\begingroup$ Interesting doc, but I can't quite follow the conclusions. kathrein-scala.com/tech_bulletins/DualPolarized.pdf Seems to suggest that you wouldn't want to broadcast horizontally, but with 45/45 antennas, you can broadcast on both. $\endgroup$ – BowlOfRed Jul 16 '15 at 8:31
  • $\begingroup$ @SebastianRiese Yes in fact C-Pol are used for satellite comms. $\endgroup$ – Noldor130884 Jul 16 '15 at 8:57
  • $\begingroup$ @BowlOfRed I read the document and am absolutely on the same wavelength (lol, we are after all talking about e.m. here), but the point I don't understand... What would really change when pol are rotated slightly (let's say 5°-10°)? Would an attenuation in one pol. be compensated by a better reception in the other? What about Co to Cross pol levels? $\endgroup$ – Noldor130884 Jul 16 '15 at 8:57
  • $\begingroup$ I know that MIMO antenna setups estimate the mixing matrix of the channels and then use this to separate the signals, this should also work for slightly offset polarization. $\endgroup$ – Sebastian Riese Jul 16 '15 at 9:13
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A motive is: "Seen from the front or rear of a handset user, the polarization will be dominated by the vertical component (the most handsets have a linear polarization because they use patch or monopole antennas), but in the lateral direction a handset is typically held at a large angle to the vertical, between the mouth and the ear of the standing or seated user, typically at least 45°."

Antennas for base station in wireless communications, Zhi Ning Chen and Kwai-Man Luk. pp. 40

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  • $\begingroup$ Cannot quite follow what you are saying... $\endgroup$ – Noldor130884 Apr 7 '18 at 7:26

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