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I have circuit demanding a 2.4Ghz antenna inside a metal enclosure. I cannot place it on the external casing since the case it's movable and will also be exposed to other issues.

I need some advice regarding antenna placement.

I thought about making a horn antenna to drive waves outside through the hole.

But then is the antenna current position right or should be vertical inside the horn (its axis to be perpendicular to horn axis)?

A profile-view drawing below:

Antenna inside metal casing

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    \$\begingroup\$ Use a patch antenna on the outside of the enclosure. \$\endgroup\$ – Andy aka Jul 3 '18 at 13:42
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    \$\begingroup\$ Antennas aren't designed to be used inside a conductive housing. A horn antenna at 2.5 GHz, hmm, the fact that you would even suggest that means you have no clue how that's done and neither have I! But I do know that antenna design takes a lot of experience to learn. Even if your solution works it will work very poorly. Antennas need an unobstructed view on the world outside, that means, do not mount it in a metal case. That's a Faraday cage, almost nothing gets in or out. \$\endgroup\$ – Bimpelrekkie Jul 3 '18 at 13:43
  • \$\begingroup\$ I think it is a good constraint that you have faced to reconsider the choice of having it in a shield. It is such times creativity and boldness pays off. \$\endgroup\$ – mehmet.ali.anil Jul 3 '18 at 13:48
  • \$\begingroup\$ @Andyaka, as I have stated initially, unfortunately this is not an option. \$\endgroup\$ – alex Jul 3 '18 at 13:58
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    \$\begingroup\$ Sure there are options, but do you understand what kind of properties these antennas have? Can you explain why they're not commonly used? Your mobile phone's reception range can be extended if you'd use a parabolic (dish) antenna. However no one uses that. Why would that be? \$\endgroup\$ – Bimpelrekkie Jul 3 '18 at 14:18
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A first and very important question: What do you want to get out of your antenna? Do you need a wide band or a narrow band? Does it need high immunity to surroundings (such as in a phone, which has to work regardless of how someone is holding it, or when it is bunched up against a face)? Do you need/want a directional channel, or do you need/want more omnidirectional behavior?

A horn could work, provided you had the room for one (at 2.4 GHz they are going to be tens of centimeters in size). Also, a horn is directional - if you want your device to work regardless of the direction, you will need to look at an external antenna.

If you had actual antenna engineers in your team you could look at fancier designs like slot antennas and leaky wave antennas, but that is not something you can design in a week, even if you are an expert no this.

Given the constraints, I would look at an external monopole/dipole, as seen in Wi-Fi routers. You can buy these off the shelf and they just "work". If you really want to design something, a patch antenna or other conformal antenna could be done on the outside of the box, but this is a lot harder. Keep in mind that the surroundings are vital - if you design your antenna to work in air, and somebody then puts a piece of plastic on top of it, your antenna will no longer work.

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  • \$\begingroup\$ We are talking about ZigBee so less than 250kbs. Our data is way less than 1kbs but I have seen 250kbps rate as the over the air fixed data rate. \$\endgroup\$ – alex Jul 3 '18 at 16:03
  • \$\begingroup\$ The box sits on the ground where people can step on it so this is why external antenna is the last option. We currently see it working on short distances, but I want to optimize. An omnidirectional behavior will be better, but I will appreciate any inputs. Tens of centimeters inside is also not the case. I have seen the slot antennas but would they work on my vertical wall (not on top, but the one with the current hole in it)? The case is a very low (6 cm in height) cilinder of 40 cm diameter. \$\endgroup\$ – alex Jul 3 '18 at 16:09

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