Building a NFC extension Antenna
If you have a near-field-communication system that operates at 13.56 MHz (or lower) I suspect, that with a little bit of clever coil winding, you can passively extend the working range (via a decent cable) to several metres.

I'm thinking you could use a local coil (by the android device) to pickup the magnetic field and connect this to a cable and, at the far end of the cable you could use a similar coil for re-emitting the magnetic field.

This would rely on good coupling to the android's magnetic field in order to capture as much energy as possible because, without "stealing" as much as possible from the originating field, the remotely placed TAG will only collect a fraction of the energy it would otherwise have received.

Some capacitive tuning on both coils (either end of the cable) may be needed.

Just an idea that might make life a lot easier than trying to build an active system that can retransmit in both directions simultaneously. The other thing is that if this idea doesn't work (even when devices are really close) then it tells you maybe that any retransmission system probably won't work due to (as yet) unforeseen technical problems.