Understanding Elliptical Polarization in Radio: Uses and Applications

[fedaykin]

What is it used for in radio, if at all?

I can't really think of anything (for circular especially) or find anything pertinent to radio.
I ask this because my electronics book mentions it, but only very briefly covers it in the radio propagation chapter.

 

[NoTime]

Use for circular -> http://adsabs.harvard.edu/abs/1975aasc.conf..148A

Haven't heard of anything specifically using Elliptical polarization though.

 

[waht]

The most common application of circular polarization in radio is the helical antenna:

http://en.wikipedia.org/wiki/Helical_antenna

Also cylindrical pipe waveguides can support a circular polarization mode. And microwave cone antennas are circularly polarized. That might be used in some radars.

 

[fedaykin]

Ah, I think I can see how it would be used for radar. You most probably won't know how whatever object you're looking at will be oriented towards you, and to get good average signal strength from an arbitrarily tilted object, a picking points from a circle (representing the magnitude of e-flux) would be best?

I hope I'm understanding this correctly. I assume I'm not, because the same would be done with radio towers for greater efficiency.

 

[trailblazer95]

are all ellipltical polarized waves horizontal and vertical polarized

 

[skeptic2]

Circular polarization, which can be considered a variation of elliptical polarization, has several advantages over linear polarization. First as Waht suggests circular polarization can be produced with a helical antenna. It can also be produced with a vertical dipole and a horizontal dipole a quarter wavelength apart and a quarter wavelength out of phase.

One advantage of circular polarization is that when the signal is reflected, the polarization is reversed eg. if you start with right hand polarization, after an odd number of reflections it will be left hand polarized. This reduces the effect of multipath on the signal and for this reason it has been used with television to reduce flutter from planes.

Another use has been to communicate with satellites that spin. A circularly polarized antenna will be able to receive the signal regardless of the polarization of the source (provided it doesn't have the opposite circular polarization).