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I'm looking at using a 1/4 wave whip antenna for a transmitter. If possible I'd like to cover the antenna in very thin (0.02 mm) aluminised kapton for reasons unrelated to the radio system; to be clear the Kapton will not be directly touching the antenna, it will be about 3 cm away. I have a feeling that although this material is very thin there is a significant possibility that I will end up with a very different radiation pattern than a typical 1/4 wave omnidirectional antenna if I surround the antenna in Kapton. I'm just not sure how to go about investigating this? I'd like to be able to predict the effect (either reduction in received signal - putting some extra factor in my link budget - or change in radiation pattern) but I have no idea where to start with this.

What is the governing principal in this scenario?

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  • $\begingroup$ Are you talking about wrapping the antenna itself in conductive film or about wrapping the antenna and some larger structure so that the film extends beyond the antenna? These are very different scenarios. $\endgroup$ – Kevin Reid AG6YO Nov 25 '15 at 15:25
  • $\begingroup$ I'm talking about having the antenna surrounded by the Kapton. But the Kapton won't be directly touching the antenna (35cm away) $\endgroup$ – FraserOfSmeg Nov 25 '15 at 15:55
  • $\begingroup$ Please edit that into your question. $\endgroup$ – Kevin Reid AG6YO Nov 25 '15 at 16:08
  • $\begingroup$ Thank you. I don't have an answer for your question unfortunately. $\endgroup$ – Kevin Reid AG6YO Nov 25 '15 at 16:33
  • $\begingroup$ @FraserOfSmeg What purpose are you trying to accomplish by putting the antenna in a larger cylinder. Also is that cylinder 3cm or 35cm in radius? What frequency will the antenna be operating in? $\endgroup$ – Rowan Hawkins Jan 19 '17 at 21:44
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Yes it will probably have a profound effect on your radio signals.

I was once involved in an experimental evaluation of some reflective window coating, to see if it would attenuate cell phone radio waves. This is a partially transparent shiny adhesive coating which can be applied to existing windows to make them more like mirror glass.

The results were fairly good, the coating reduced the radiation by up to 30 dB compared to uncoated glass.

So I would assume for a starting point, that any shiny metallic coating on plastic or glass is fairly conductive to RF and block the signal, even if if the plastic is not touching it.

Edit after re-reading your question: if the metallised foil is a cylinder, concentric to the 1/4 wave antenna, shorter than the antenna, and not touching the metal groundplane, then its only effect will be to slightly detune the antenna. If you are able to measure the antenna impedance, you can just cut it for the right frequency again.

Last edit: car windscreens sometimes include a metallic coating to help reject solar radiation. This coating is so thin it doesn't make the windscreen noticeably shiny at all, but it still affects radio reception. For example, a GPS receiver doesn't work through such a windscreen.

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  • $\begingroup$ Vehicle tints are not always metallic however the metallic ones will block glass mount cellular antennas. way back when I worked at Verizon, if we were lucky and the tint was a not embeded in the glass, we would remove remove a portion of of the tint for the antenna, that was at UHF. $\endgroup$ – Rowan Hawkins Jan 19 '17 at 21:40

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