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wlchan
Joined: 10 Jun 2004
Posts: 5
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 09 Aug 2004 9:08 What is circular polarization |
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Dear all,
Can anyone explain in details about the circular polarization, thx
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sergio mariotti
Joined: 22 Dec 2003
Posts: 467
Helped: 42
Location: Italy
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09 Aug 2004 14:58 What is circular polarization |
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as you may see the Electromagnatic (EM) wave, propagating along z axis, is a combination of 2 cyclic E & H fields, placed on zx and zy plane (they are 90° phased).
Looking, for semplicity, to |E| plane only, if it "position" is zenithal, the wave is called " polarization linear vertical" , if it is placed "orrizontal" then the wave is called "polarization linear orrizontal".
The assumption done until now is that if the EM wave is propagating, the polarization don't change.
But what happen if the |E| fiels rotate along its axis (spin) during propagation? You'll get a circular polarization!
The "linear" polarization is a general case of the circular one.
E.g. the linear |E| may be thought as a combination of 2 vectors rotating at 2*3.1415*freq [rad/sec] but in opposite directions (CW & CCW).
If amplitute is the same and phase is 0° you'll get vertical linear wave, if they are same amplidute and 90° phased, you'll get orizontal linear, if one has amplitude=0, you'll get circular wave.
As for linear polarization, the permitted circular polarizations are 2: Left handed and rigth handed, and of course all combinations.
Rem: definitions: IEEE follow the Kraus definition. The Optic scientist use the opposite definition, this cause lot of error in practice !!!
Rem: inside the most of the transmission media, only 1 polarization (and often only one mode) is permitted. the exeptions are circular and square section waveguide.
A very complete and comprensive tratement may be found on Kraus- Radioastronomy.
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eltonjohn
Joined: 22 Feb 2002
Posts: 1751
Helped: 28
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09 Aug 2004 17:20 Re: What is circular polarization |
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I think that sergio was very complete in the explanation /
I will just give you some technical examples .. The antennas for circular polarization are just that ,CIRCULAR .. You know the yaguis arrays, well they are linear . so in order to receive the maximum amount of energy the reception antenna also should match the angle of the transmision antena .Circular polarization antennas . allow to receive energy at any angle .One example are the Broadcast FM antennas .. they look like an array of RINGS ,that's why with fm radios you can move it around and are still able to get a fair good reception!
cheers
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09 Aug 2004 17:20 Ads |
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flatulent
Joined: 19 Jul 2002
Posts: 4877
Helped: 324
Location: Middle Earth
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09 Aug 2004 17:42 Re: What is circular polarization |
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Another advantage of circular is that the transmitter can be rotating. This was done in early space satellites that were not stabilized. They could tumble and the reception was not degraded.
When circular polarized waves are reflected, the rotation is reversed. This allows a reduction in multipath interference. The receive antenna only responds to the direct path and double reflections which are usually much lower in amplitude than the direct path waves.
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salem_sajid
Joined: 28 Jun 2004
Posts: 57
Location: Pakistan
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13 Aug 2004 0:04 What is circular polarization |
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I am not sure if u know this or not.Circular polarization is genrally used in bad weather conditions and in not so good environonment in radars to detect the targets as it suffers less than other. Its also the choice in fire control radars mostly. How ever in good weather its performance is less than other polz.
Regards
Ess ESS
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mahdithdn
Joined: 18 Aug 2004
Posts: 101
Helped: 13
Location: Iran
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18 Aug 2004 13:23 Re: What is circular polarization |
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| circular polarization is simply composed of two orthogonal linear polarazation e.g. vertical & horizontal.
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Ahmed Ragab
Joined: 30 Jun 2004
Posts: 350
Helped: 118
Location: Egypt
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19 Aug 2004 1:13 Re: What is circular polarization |
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Well to understand circular polarization imagine the following:
u got an electric field consisting of an x-component and a y-component; E= 10cos(wt) ax + 10 sin(wt) ay
notice that the 2 components are out of phase by 90 degrees
now when the x- component is a maximum u find the y-comp a minimum
and vice versa
the resultant shape of the electric field is a vector rotating in the xy-plane
this is called a circularly polarized field.
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