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Can one construct a filter out of nothing but pure metal that will pass only right circular polarized radiation and reflect left circularly polarized radiation?
What would it look like? A helical spring in a tube?
What about a twisted metalic ribbon inside a circular conducting tube?

An axial mode helical antenna transmits circularly polarized radiation.
If I put an axial mode antenna (perhaps with a resistive load?) in a waveguide, can I create a filter that passes only say left circularly polarized radiation?
I would ideally like to do it with only conductive (i.e. not resistive) material.
I would also like it to reflect (not absorb) radiation of the opposite circular polarization.
Can someone tell me how to do this?

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Without giving a range of frequency at least, nobody really can help You. –  Georg Jan 30 '11 at 20:55
By the way the question is written, he's clearly talking about radio waves of reasonable frequency; that is say, between centimeter and meter. –  Carl Brannen Jan 31 '11 at 0:38
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up vote 3 down vote accepted

From the way your question is written, I believe that you already know how to make a wave guide that will split horizontal from vertical waves. I'm assuming that you also know how to combine and split radio waves. Furthermore, I'm going to assume that you can build a "splitter", that is a device where radio waves come in and are split into two outputs, one where the horizontal waves go the other where the vertical waves go.

So build a horizontal and a vertical wave splitter. Combine their outputs and inputs so that they are sufficiently out of phase and the combined apparatus will be a circular splitter. This is a matter of applying the law of superposition.

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