The iPhone antenna is located in the upper 1/3 back side of the phone.
There is no fixed NFC antenna position for each brand of Android phone because the shape and form of the phone is different. For detailed NFC antenna locations, please refer to the original manufacturer's manual of your own device.
NFC at top
NFC at middle
NFC at buttom
Nukii's Antenna Location
Nukii's antenna is located at the end where it is printed with the word Nukii and is available on both sides.