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So, I was annoyed that my Yagi antenna was enclosed in a plastic-tube, which lets it roll around and fall off the table occasionally, but without its enclosure the elements hooked in anywhere. So I wondered, since the material (I assume it's PVC) is radio-transparent anyways: Couldn't the antenna be enclosed in other shapes as well - as long as they are radio-transparent?

Note: The antenna I'm talking about is just a simple 19 Element (17 Directors) Yagi antenna for 2.442 GHz home Wi-Fi.

Basically my questions are:

  • Is it ok to completely enclose the elements themselves - or do they have to have air (or any free space) around them?
  • Is the boom required to be at the center?
  • Does the boom actually have any effect when it's radio-transparent and non-conductive anyways?
  • Would it affect the Antennas performance, if there were two (non conductive) booms, holding the elements with their edges?

I just wondered about this, because I remembered my physics teacher telling us (decades ago), when frequencies are involved, things vibrate/oscillate. A tight enclosure might hinder this eventually.

I have drawn (sorry for my rather poor paint-skills) two designs, which I would like to try out.

Enclosed design

This first design would enclose all elements in pockets, to prevent them from moving and possibly even corrosion if it's airtight.

Ladder design

This ladder-type design was just an idea to save some PLA material first, with just the benefits of saving space and preventing the elements from hooking in anywhere.

I know one could probably simply slide the original Yagi inside some sort of flat plastic sleeve - keeping its boom, and keeping the elements "free". But such projects simply trigger me ^^ - and the antenna that I bought is manufactured rather... "creative"... so I'd like to rebuild this whole thing anyways.

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    \$\begingroup\$ PVC certainly isn't radio transparent this close to the elements. It has a relative permittivity that will mess with tuning significantly. \$\endgroup\$
    – Andy aka
    Sep 14, 2018 at 13:18
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    \$\begingroup\$ Some say it is, some say its not, and others say it depends on the sort of PVC-tubing. Do you know if PLA is more/less/equally radio-transparent (simple white PLA)? Is there a minimum distance to keep between an Element and any sourrounding Material to be safe? I guess this already nihilates my designs, since there's a lot more contact between the elements and other material. So the boom is at the center simply to keep as much free space around the elements as possible? \$\endgroup\$
    – Lightweight
    Sep 14, 2018 at 14:59
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    \$\begingroup\$ The centers of the elements are current nodes (low impedance), while the ends are voltage nodes (high impedance). Putting nonstandard dielectric materials near the ends will detune the antenna more than anything placed near the centers. \$\endgroup\$
    – Dave Tweed
    Sep 14, 2018 at 19:35
  • \$\begingroup\$ @Andyaka is right – PVC has a (relative) dielectric constant, depending on the type/density of the product of 3.7 at low frequencies down to 2.8 at around 1 GHz. So, yes, non-uniform cladding, especially close to the conductor ends, will change the properties. Generally, that'd significantly reduce the wave length in the medium, which will, very complicatedly, de-tune the intra-element spacings and lead to greatly reduced efficiency as an antenna. \$\endgroup\$
    – Marcus Müller
    Oct 29, 2018 at 19:09
  • \$\begingroup\$ Alternatively, if the antenna were designed with your enclosure idea originally, it would work fine. But the design of the antenna would be different, for sure, and it's not guaranteed it would be possible to get exactly the same characteristics or performance. My instinct says it's possible to make a sufficiently capable antenna with your enclosure idea, though. \$\endgroup\$
    – Shamtam
    Nov 3, 2018 at 17:43

1 Answer 1

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If I understand you well, your problem is that the shape of the enclosure of the antenna is cylindrical. (Or is the antenna wound up for transport/storage?) If the antenna is used lying on a table, you could attach (glue) two little light plastic or paper pieces to it to prevent it from rolling.

Some general remarks: All plastic materials have a dielectric constant that modifies the behavior of the antenna. The only neutral zone is the boom, if it is located in the centre. There it does not matter if it is conductive or not. Putting plastic material around each element of the antenna (radiator, reflector, director) would definitely change the behavior of the antenna. The same holds for putting anything along the ends of these parts. If the antenna is usable as is, better leave it like this.

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  • \$\begingroup\$ Thank you for your answer. Yes, it was the cylindrical shape, that annoyed me for various reasons. It would also be much easier to attach a wifi-controller at its side :) When you're saying Elements are neutral at their center - is there a minimum distance around an element in general, at which an enclosure wouldn't affect the antenna's performance (theoretically). For example, if the Reflector was 60mm long and the folded dipole was 20mm wide, would it affect the performance, if the whole antenna would be enclosed in a rectangular tube, that is 70mm high and 30mm wide? \$\endgroup\$
    – Lightweight
    Nov 4, 2018 at 17:43

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