P3D Re: polarization

[Tom Hubin <thubin@xxxxxxxxx>]

Hello Bob,

> I have kind of an intuitive feel for microwave circular polarization
> as used in satellite transponders, where the E and M fields exist
> at right angles to each other and energy is transferred back and forth
> between them as the wave travels.

Light is the same as microwave as far as the way the E and M fields
behave. There is a curious difference in custom. The definitions for
right and left circular for microwave are the opposite of the
definitions for light. 

For light, RHCP (right hand circular polarization) is when the
polarization rotates clockwise as the light approaches you. For
microwave, RHCP is when the polarization rotates clockwise as the
microwave travels away from you. These conflicting definitions cause
some confusion when you read the two kinds of textbooks and try to come
up with a unified explanation. They also raise hell with the math.
 
> Also that if you have, say, a
> right hand circular polarization signal and you use an antenna
> this is left hand, you get at least a 3db loss (ie, reduced by
> 1/2).

I would expect that circularly polarized signals reaching a linearly
polarized antenna like a simple whip end up with a 3dB loss. Just as
circularly polarized light loses 50% or 3dB or 2 stops when passed
through a linearly polarized filter. 

I would expect that circularly polarized signals reaching a circularly
polarized antenna of the opposite type would result in an infinite loss.
The same as passing circularly polarized light through a circular
polarizer that is of the opposite handedness of the light.

Tom Hubin
thubin@xxxxxxxxx
AO Systems Design


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End of PHOTO-3D Digest 3428
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