Help with the design of a rectangular loop antenna for the PN532 controller for NFC communication
I'm no expert on 13MHz-carrier data-transmission but i do come from a background of transmitting power magnetically to rotating circuit boards and receiving modulated data back at 80MHz so if I've misunderstood anything please let me know.


  •Could it be acceptable to put the components (NFC controller, LED > driver) on the same PCB as the NFC antenna?


Yes this is acceptable but keep circuits as far distant as possible so that the receive side stands the best chance of working effectively.


  •What would be the "best" position relatively to the antenna in this
  case? (i.e. one that would limit eddy currents and inductance
  increase)


According to the very long-winded document you linked, the antenna Q needs to be a bit less than 30 and this is easily checked by using standard oscilloscopes and signal generators. Q is centre frequency (i.e. 13.56MHz) divided by 3dB bandwidth and for a Q of 30 bandwidth will be about 450kHz.

So you need to make sure your centre frequency is spot on and that you have chosen Rq values to limit the Q sufficiently or you'll be possibly breaking some regulations about emissions levels.

I'd position the antenna and compensate for eddy current effects (frequency and Q changes) with a slight retune then add or remove a little bit of Rq to give a Q of 25 to 30.


  •How to efficiently shield the main controller board? Will a sheet of
  copper do the job(instead of ferrite)?


You may not need to do much (if anything) here but I'd recommend using the proper ferrite sheet (Ferroxcube used to sell it because I've used it). Using copper sheet may detune and slightly desensitize the antenna depending on how close to the antenna it is.


  •Is there an advantage to have different length and width for the
  antenna?


Yes, the squarer the better. Bearing in mind this is magnetic coupled data and you should be looking for a loop with as much inductance as possible but not so much that it's self resonant frequency is lower than (say) 15MHz.

As a simple idea about inductance - inductance is defined as total flux produced per amp. The bigger the cross sectional area, the more flux is produced per amp. A long thin loop however has less inductance than a square loop of the same area.