Passing light through a circular sieve: Well, actually, let’s think about radar or microwaves with a wavelength of order a centimeter or two, so you can tailor your aperture, say by etching a silver screen on glass. If you have a reflective metal screen, and you cut a long narrow rectangle in it, it will pass (some) photons of the properly oriented linear polarization of wavelength shorter than the length of the rectangle. What if you cut a narrow circular annulus into your screen? Would it pass circularly polarized radiation of the proper wavelength? Bonus Points: What about an elliptical annulus? Please ignore photons of wavelength shorter than or comparable to the narrow dimension of the slit.