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.
When I first read your question I assumed the following:
- You are trying to track your clients' movements using your clients' smartphones
- Your clients would have to install an app on their smartphones in order to enable this
Then I saw the discussion about hacking the smartphones to change their antennas. This would imply that you would be providing the phones and giving them to the clients.
Hacking a cellphone to make it read NFC at a greater distance, would IMHO be quite a difficult task. As has been pointed out, NFC is specifically designed to limit distance (for privacy and security considerations, I believe).
Unless I'm missing something... if your scheme requires giving them something to carry with them in the clinic, you might just as well give them RFID tags, and place RFID readers in the doorways.
On the other hand, if you want to use the clients' cellphones with a downloaded app, as another poster suggested, Bluetooth low energy beacons might be a better approach, as BLE is designed to be readable at a greater distance.
Best Answer
Even coaxial cable will have some attenuation, and although it may not be huge, it still subtracts from the link power budget.
Just how much it will subtract depends on the specific type of cable used (there are other things involved, but in this context it comes down to the cable alone), but the short answer is that any added length of connecting cable from the antenna to the actual receiver or transmitter will reduce the effective range of the system when viewed from an antenna to antenna perspective.
Whether the change in effective range is noticeable will depend on the characteristics of the cable, and will go from indiscernible to noticeable (coax varies widely in attenuation characteristics depending on the specific one used).