antenna-theory.com

[GinoMan2440]

I'm spec-ing out a computer that I want to create which has a very small case... as part of it, I'm using a motherboard which has an internal wifi card but it connects to external antennae at the back which you're expected to use.... I don't want to use them... in fact in leu of different ports on other connected components, I'm only using some of the motherboard's backside ports. I would like to internalize the wifi antenna (I'm already doing so for a couple of the controller components, an XBox360 controller receiver and a logitech device that gives you a hand-held mouse and keyboard by imbedding a usb controller inside the case with the stock recievers) but I want to put a wifi antenna in this case:

http://www.newegg.com/Product/Product.aspx?Item=N82E16811133093

but most of it except the face is made of metal... I read somewhere that the metal will interfere with any internal antennae but the mac mini is an aluminum chassis with the antenna at the bottom. In addition the antenna is mounted on an antenna plate which looks like a grated semicircle, and then inside the plastic lid that closes it off at the bottom there's a metal lining. I'm not sure how it works but it's obviously possible to internalize a wifi antenna inside a metallic case.... how can I do something similar in a way that's aesthetically pleasing?

[Schubert]

"Obviously possible to internalize an antenna inside a metallic case"

No. It has to be outside of the metal or a sufficient area without metallization. Electromagnetic signals cannot penetrate metal housing. Find an area where you have an aperture (non metal area) in which to place the antenna.

[GinoMan2440]

I suppose I could put it in the plastic face but then... THE APPLE LOGO! sorry, I had an aha moment... that's how they do it... the case traps the wifi signal inside but it can get there because of the apple logo on top and the plastic casing in the bottom... any reflected wifi signal makes it inside the case.... so I should be ok putting it inside the face then because.... ok I get it. is there anyway I could turn the metal case into the antenna iPhone 4/4S style?

[Schubert]

The signal doesn't bounce around on the inside of the device. You won't be able to transmit and receive simultaneously if that happened (i.e. transmit signal power is +15 dBm and received signal power is -70 dBm........ you're transmission will destroy the reception).

Anyway, the ideal solution is to find an aperture and make a self contained antenna. This means it should be metal backed, so that the signal does not enter the metallic box. The only thing exiting your antenna should be the cable that goes to your radio.

That's a little tricky because the antenna design is much harder. If you have enough space you could use the metal chassis as one arm of the dipole and run a second arm inside (along the surface away from the metal) to make the second dipole arm [they don't have to be perpendicular]. The reason this is crappy is because you'll have strong transmit fields screwing with your electronics.....and also a lot of lost energy for what is transmitted inside the box.

Anyway, here is a page from this site about cavity backed slots:
http://www.antenna-theory.com/antennas/aperture/slot2.php

[bigSteve]

While discussing development of the iPhone and it's relationship to the metal backed iPod, an apple designer states:

"and you can’t get antennas to work properly in a fully enclosed metal jacket. So each one of those things needed to apply other features that started."


This was noted by former Apple industrial designer Douglas Satzger, during the Samsung vs. Apple patent infringement trial that is currently ongoing.

[quote referenced from: http://9to5mac.com/2012/08/02/former-apple-designer-reveals-apple-passed-on-a-curved-glass-iphone-due-to-cost/] on 8/2/2012