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I have built a gadget that can make pictures using ambient 12GHz radiation.

The nature of the parts I used (commonly available satellite TV parts) means that I have selectable polarization on the receiver. I have therefore the equivalent of a polarized lens.

I thougt it would be fun to replicate the common two polarizer experiment, but using 12GHz waves instead of visible light.

Problem is, I don't think a typical sheet of polarized plastic would have any effect on RF. Not to mention the problem of finding such a sheet of at least 1 meter square.

It seems to me that whatever the structure is in the polarizing lenses used for visible light it must be of approximately the same scale as the wavelength of the waves. Not precisely at a particular wavelength, though, since regular polarizers operate over the entire visible spectrum. So there has to be some dependency of the wavelength, but it isn't a really tight connection.

I would therefore have to make some kind of grid with features around 2.5cm (wavelength of 12GHz RF.)

What would the structure have to look like? Lots of parallel slots? If so, how could I determine the spacing?

I assume it would have to be made of metal. Something like aluminum foil. Whatever I use must have low emmisivity (I think) else the black body radiation of the polarizer would overwhelm the radiation from whatever I'm using as a source.

So:

  1. What would the structure of such a polarizer look like?

  2. How would I go about calculating the size of features in the polarizer?

  3. What material properties will I need in whatever it is that I make the polarizer from?

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  • $\begingroup$ Wires are easiest, I would think. $\endgroup$ – Pieter Feb 23 '18 at 20:59
  • $\begingroup$ @Pieter: Well, maybe. Or maybe the strips need to be of a particular width as well as a particular spacing. $\endgroup$ – JRE Feb 23 '18 at 21:05
  • $\begingroup$ The spacing should be small enough. Maybe one could use an old badminton racket. $\endgroup$ – Pieter Feb 23 '18 at 21:12
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    $\begingroup$ wires wrapped across a pair of threaded rods is the typical easy way $\endgroup$ – Martin Beckett Feb 24 '18 at 4:03
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All you need are parallel stripes of metal with spacing and width smaller than the wavelength. This is called a wire grid polarizer. The smaller stripes the better; aim for a 50% duty cycle. You could maybe try stretching out a piece of aluminum foil and cutting parallel stripes a few mm’s apart (maybe support it with cardboard). The waves polarized perpendicular to the stripes will be transmitted.

Have fun!

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  • $\begingroup$ Thank you for your answer. The expression I needed was "wire grid polarizer." Now that I know what to call it, I've been able to find information about how they are made, and how the spacing and wire size relates to the frequency. $\endgroup$ – JRE Feb 24 '18 at 19:35
  • $\begingroup$ @JRE My pleasure! Just remember that the transmitted polarized waves are perpendicular to the wires. It’s a little counterintuitive because you might think the waves “slip through the gaps”, but that would be incorrect. $\endgroup$ – Gilbert Feb 24 '18 at 19:46

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