Linear , elliptical polarization

[max232]

hi ;

The polarization is imprtant in propagation between transmitting and receiving antennas,there are 2 types of polarizations :
-Linerear polaerization
-Elliptical polarization ( circular polarization ),

How one selected one of these two types??? :roll:

Thx

 

[flatulent]

If the two ends of the pat are fixed linear works well generally. If there is rotation of the polarization by the media in between or by one end rotating like a space satellite, circular works best.

 

[StoppTidigare]

Hi all since we´re discussing polarization. Maybe somebody knows why a radarwave with circular polarization backscatters less from rain than linear polarization ?

Regards,
StoppTidigare

 

[flatulent]

Rain drops are not perfect spheres and can convert linear polarized waves into circular. This is why using circular rotations of opposite directions on the same frequency as a way of being able to double the data rate do not work on radio paths through rain. The drops cause crosstalk between them. Using two orthogonal linear polarizations work better.

The RADAR reflections have some of the power converted to the opposite rotation which is rejected by the receiver. Also each reflection of a circular wave from an ordinary reflecting surface changes the rotation so multipath with an even number of reflections are also rejected.

 

[galilu]

can we generalize the case of RADAR to all ground station for Satellite communication?

 

[flatulent]

Satellites are a special case where they are so high in the sky that there is no multipath reflections from the ground or other objects. Also, the radio path goes through rain areas the shorter dimension (vertical) as opposed to lengthwise horizontal and therefore has less rain attenuation. There should be less circular polarization crosstalk. I do not know if they use polarization diversity to double the throughput. They sometimes use multiple antenna beams to reuse the frequencies.

 

[yuen_cityu]

Circular polarization is necessary for systems operating at frequencies below about 3 GHz since the Faraday rotation produced by the ionosphere can cause a linearly polarized transmitted signal to rotate out of alignment with the receiving antenna.