Electronic – What type of antenna does the Xbox One controller use and how can you disable it

antennapcbpcb-designRFwireless

I recently cracked open an Xbox One controller, the impetus for doing so was two-fold:

  1. First and foremost the engineer in me likes to see how things work under the hood as I learn a great deal that way
  2. Secondly, I wanted to mod my existing Xbox 360 fight-stick controller to work with the Xbox One by splicing into the Xbox One's PCB for button presses; this is colloquially called "pad hacking."

I was able to successfully mod my controller to utilize the Xbox One's PCB and now my attention is aimed at electrically disabling the wireless functionality. The reason this is necessary is that wireless communication is forbidden in fighting game tournaments due to the possibility of your controller affecting the inputs of your opponent (or vice versa.)

It's been a loooong time since I studied RF but I'm fairly certain that the antenna circled in blue in the picture below is an Inverted-F Antenna (IFA), is this correct?

I had thought that physically de-soldering the antenna would prevent the controller from wirelessly connecting, but I was wrong! It still connected at a distance of about 6-8 ft.

Next I thought that cutting the trace on the bottom side of the board leading to the antenna (shown in red) would surely do the trick but again I was wrong; it would still connect if I was within a foot or two of the Xbox One. As an aside, what exactly is that trace's functionality? Continuity tests shows to be at ground potential (this board has a common ground). Originally I thought this was the feed line but now I'm thinking this is the shorting trace which acts like a parallel inductor. Any ideas?

So what kind of voodoo is going on here, I had thought that to get a device to properly radiate in a functional manner requires all the right parts in all the right places. This board, however, seems to be built like the terminator; it just keeps working. Besides putting it into a Faraday cage, can anybody offer up suggestions on how to electrically disable this PCB from radiating?

As a side note, I'm not 100% sure what frequency band the Xbox One controller uses but if I had to guess it would be 2.4Ghz as that is what its 360 predecessor used.

Front side with Antenna

Back Side with cut trace

EDIT

Here is zoomed in picture of the trace that I cut. I followed the trace with blue dots so you can see how it connects to the antenna on the other side of the board. The trace appears to have an SMA connector as well as AC-coupling cap in series.

Zoomed in picture of trace cut

Best Answer

Next I thought that cutting the trace on the bottom side of the board leading to the antenna (shown in red) would surely do the trick but again I was wrong; it would still connect if I was within a foot or two of the Xbox One. As an aside, what exactly is that trace's functionality?

The red line you cut IS the antenna path. But not it's radiation source. The reason it now only connects at 1 foot instead of its usual range is because you crippled it. Two ways to completely (for practical purposes) remove the signal is depower the entire antenna/wifi section, which the sub-board is, or connect the antenna trace to ground.

For theory, Antennas should be a full or 3/4th or 1/2, or 1/4th of the wavelength for optimum propagation. Just because it is not that size does not stop it from working, it just stops it from working well. Your antenna is now a few millimeters long instead of a few inches.

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