I know it's a bad idea!

Well, we are developing a project which requires an RF transciever. And, we are using a metallic cabinet to give it a premium finish! And, this premium finish is so important to us that we can not make a compromise with it!

So, what all options do we have to minimize the adverse effects of the metallic cabinet on the RF signal quality? Can we use the metallic cabinet itself as the antenna?

Any guidance is greatly appreciated.


Abbas.

 

What will you use as your signal ground, if the cabinet could be made to work as an antenna?
What frequency RF?

 

What kind of antenna are you planning to use?

 

What frequency RF?

The 2.4 GHZ Wifi band.

 

What kind of antenna are you planning to use?

Sorry, not am very good with antennae!

We are planning to using SMD antenna on the PCB itself, avoiding any protruding patch antennae.

But, if there's a way, we might use the metal cabinet as an antenna, through an impedance matching circuit.

I don't know!

 

if there's a way, we might use the metal cabinet as an antenna, through an impedance matching circuit.

Not likely.
The metal cabinet will act like a Faraday cage.
But you could place a small, external antenna on the outside of the cabinet (on top, for example).

 

You might be able to make a slot antenna at that frequency but it would require a enclosure design that will allow you to build the antenna coupling cavity inside.

http://www.antenna-theory.com/antennas/aperture/slot.php
You can direct connect the feed to the slot too but it still should have a cavity behind the slot.

 

You might be able to make a slot antenna at that frequency but it would require a enclosure design that will allow you to build the antenna coupling cavity inside.

http://www.antenna-theory.com/antennas/aperture/slot.php
You can direct connect the feed to the slot too but it still should have a cavity behind the slot.

Thank you for sharing the video, nsaspook, I really appreciate it. Unfortunately, we have a very limited space, and can not employ an antenna requiring such a cavity.

Need to figure out something else.....

 

hi Abbas,
If you cannot compromise on the metallic cabinet, I would say you will have to rethink that limitation, else you do not have a product.
There are some plastic enclosures that have a 'metallic' appearance.
May I ask why the problems in mounting a transceiver inside a metallic case were not discussed in the design stage.?

E

 

I know it's a bad idea!

Well, we are developing a project which requires an RF transciever. And, we are using a metallic cabinet to give it a premium finish! And, this premium finish is so important to us that we can not make a compromise with it!

The only thing I can think of is to adopt the strategy of phone and computer makers and machine a part of the enclosure so that a plastic panel can be used to mount the antenna. It can be done in such a way to enhance the appearance. The plastic cab be matched or contrasting, in any case, turned into a design element.

 

hi Abbas,
If you cannot compromise on the metallic cabinet, I would say you will have to rethink that limitation, else you do not have a product.
There are some plastic enclosures that have a 'metallic' appearance.
May I ask why the problems in mounting a transceiver inside a metallic case were not discussed in the design stage.?

E

Thank you for your reply, ericgibbs. We are planning to add an extra feature, if that doesn't cause us a lot of overhead. For the product, the team thinks this effort is worth it.

 

The only thing I can think of is to adopt the strategy of phone and computer makers and machine a part of the enclosure so that a plastic panel can be used to mount the antenna. It can be done in such a way to enhance the appearance. The plastic cab be matched or contrasting, in any case, turned into a design element.

Thank you for your reply, Yaakov. That's how we are planning to proceed. But if we could get some additional guidance and direction that reduces our expenses, in terms of money as well as time, it would be really great.

 

Thank you for your response, ericgibbs. We are planning to add an extra feature, if that doesn't cause us a lot of overhead. For the product, the team thinks this effort is worth it.

hi Abbas.
Sorry if I sound picky, but what sort of statement is that as a response.?

Eric

 

There are many antennas so this is a random example: https://www.inventeksys.com/wp-content/uploads/W24P-U_2.4Ghz_-Antenna_Specification.pdf

An antenna like it, bonded to a plastic insert on the case, would "work" but keep in mind the performance of the antenna will be affected by the surrounding case, and though I can't provide any rigorous guidance on how much space should be left between the antennas edges and the metallic case, there will need to be some. From what I can guess at, you will need about 10mm to avoid problems, but that is not rigorous engineering advice.

 

hi Abbas,
If you cannot compromise on the metallic cabinet, I would say you will have to rethink that limitation, else you do not have a product.
There are some plastic enclosures that have a 'metallic' appearance.
May I ask why the problems in mounting a transceiver inside a metallic case were not discussed in the design stage.?

E

Heh, I deal with this everyday...

Marketing: Case needs to be metal; pretty shiny metal, the users demand it!!!
Engineer: Uh, can't get RF out of a metal box very easily if at all
Marketing: Shiny... metal
Engineer: But physics
Marketing: Users, shiny, metal and my buddy's son-in-law is an unemployed electrician and he says you can do it. Let's just do it and give it a try.
Engineer: <shrug> whatever
[Prototype can't transmit out of the enclosure let alone to where it needs to go]
Marketing: Why this not work?
Engineer: physics
Marketing: Why do engineers make things so hard? Need shiny metal purdy

 

I have not laughed so much in a long time. Reminds me of the old days at Apple. "Steve wants to do it this way..." You do your best. What else can you do?

Also,

 

That was my 11 o'clock meeting today.

 

One fundamental question concerns directionality (i.e. does the radiator need to work mainly in one direction or all directions equally?); also, over what distance does it need to work (i.e how effective/efficient does it need to be?).

To address the metal box question, start from the premise that a sealed metal box will not allow the escape of RF energy. Simple. If any does escape, it's because it isn't sealed, because there is a slot or large holes or because the cabling is not adequately screened or bypassed. But because you actually want RF energy to escape the box, either an external antenna or some kind of opening that radiates is essential. Some kind of slot radiator or even a horn would be possible, as has been referred to elsewhere, but it will be directional. Antennas can be made in many shapes and sizes, so if you absolutely 'must' have a metal box then there will probably be a design that will work, somewhere, provided you make slots in it. If it was me I'd attach a coaxial cable to the output of the WiFi transceiver and add it to the cabling bundle going out of the box, then use a coaxial sleeve antenna externally, such as you can see on most home WiFi routers.

If you have any holes in the box larger than a percentage of the wavelength, say around a centimetre at WiFi frequencies, you will get RF leaking out (desirable!) so best idea is to try it and see if it works over the distance and in the direction you need it to, and then revise your design until it works.

I hope this helps.

 

What is the shape and dimensions of the cabinet?

 

https://www.ifixit.com/Answers/View/215259/How+does+the+antenna+design+on+the+iPhone+6+work