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Author Topic: Polarization: Difference with antennas oriented at 315/45 and 0/90 degrees?  (Read 635 times)

Miguel Dahl

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I understand why you'd want a 90 degree opening between the antennas. But Is there a noticeable practical difference between orienting them 1) 135 and 45 degrees or 2) 0 and 90 degrees? Both form a "V". AFAIK the reception is on par even if the Tx is flipped 180 degrees comparing to the Rx, as the polarization is still 0 degrees offset.

I guess 135/45 better since most often, in most situations the microphone or beltpack(antenna) is oriented close to vertical? There are some people who use a beltpack-belt and place the beltpack horizontally, would a 0/90 orientation be better in those situations, for that one particular beltpack, in theory?

« Last Edit: February 16, 2020, 11:57:17 am by Miguel Dahl »
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Jason Glass

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I understand why you'd want a 90 degree opening between the antennas. But Is there a noticeable practical difference between orienting them 1) 135 and 45 degrees or 2) 0 and 90 degrees? Both form a "V". AFAIK the reception is on par even if the Tx is flipped 180 degrees comparing to the Rx, as the polarization is still 0 degrees offset.

I guess 135/45 better since most often, in most situations the microphone or beltpack(antenna) is oriented close to vertical? There are some people who use a beltpack-belt and place the beltpack horizontally, would a 0/90 orientation be better in those situations, for that one particular beltpack, in theory?

You're correct that there is no difference between 0 and 180 in regard to polarization matching.

IMHO, in our work, best practice is to attempt matching the angle of both ends of a link having linear polarized antennas.  But diversity complicates that idea and it's arguable that the angle relative to the horizon is immaterial as long as diversity A and B are separated by 90.  In modern low power systems, a link often can be sufficient via reflections when direct signal is cancelled by a different reflection.  Keep in mind that each reflection rotates its polarization per its angle of incidence.  So the angle of a fixed antenna at one end of the link relative to an unpredictable moving antenna at the other is arbitrary when the intention is to receive random reflections.

However, in terrestrial point-to-point fixed links antenna angle relative to horizon can be crucial.  Especially in high power long distance systems where reflection and diffraction off of Earth and the ionosphere are unavoidable parts of the link.

Miguel Dahl

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You're correct that there is no difference between 0 and 180 in regard to polarization matching.

IMHO, in our work, best practice is to attempt matching the angle of both ends of a link having linear polarized antennas.  But diversity complicates that idea and it's arguable that the angle relative to the horizon is immaterial as long as diversity A and B are separated by 90.  In modern low power systems, a link often can be sufficient via reflections when direct signal is cancelled by a different reflection.  Keep in mind that each reflection rotates its polarization per its angle of incidence.  So the angle of a fixed antenna at one end of the link relative to an unpredictable moving antenna at the other is arbitrary when the intention is to receive random reflections.

However, in terrestrial point-to-point fixed links antenna angle relative to horizon can be crucial.  Especially in high power long distance systems where reflection and diffraction off of Earth and the ionosphere are unavoidable parts of the link.

Thanks, as usual :)

The thing with coverage area, and angles of polarization after the signal has reflected off something makes this even more interesting.
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Gian Luca Cavalliini

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two interesting case in my experience:
1) limited space for tx and rx antenna: LPDA for tx 0 degrees, near rx 90 degrees, far rx 0 degrees. It helps in avoid desensing the near rx channel.
2) In Italy we have tons of DVBT, we don't have really free channels... so often we need to stay ABOVE (not so low) noise floor from DVBT. Well, pointing LPDA away makes great sense. Using polarization mismatch with DVBT (usually orizontal) is sometimes good additional help

BTW: anybody ever tried to use 90degrees with diversity IEMs? I know is not so pratical to insert a right angle SMA M/M to one of the antennas, but... just curious if could be any improvements this way with A1031 (omni polarized) with a center stage in big arenas.
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Miguel Dahl

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I forgot to add that the reason I asked the initial question is that I've always been taught to do 135/45. I saw a pic yesterday where one guy did 0/90. I got curious and looked up shures website for tips and tricks for WL, and they recommend 135/45, so the question was more steered towards "Why do shure recommend 135/45 and not 0/90?"
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Jean-Pierre Coetzee

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Maybe the likely hood that the 0 antenna is closer to the floor/surface and therefore can be closer to a metal object that would detune it.

This is a thumbsuck though
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Tim McCulloch

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My memory of RF polarity goes back to satellite transponders, each having separate 'program material' on horizontal and vertical beams.  Back in the C band days of watching Ma Bell's terrestrial microwave "march" through the video material... downtown Kansas City, MO was a challenge...
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