A reader device includes an array of antenna coils configured to electromagnetically couple with devices implanted beneath or within skin of a human body. An implanted device can include a loop antenna or other means configured to couple with at least one antenna coil of the reader device to receive radio frequency energy from and transmit radio frequency transmissions to the reader device. The antenna coil array is configured to mount to the skin surface to improve the coupling between the implanted device and coils of the array. Further, the reader device is configured to select one or more antenna coils of the array and to operate the selected antenna coil to communicate, via radio frequency transmissions, with and/or provide radio frequency power to the implanted device. An antenna coil of the array can be selected based on a detected amount of coupling with the implanted device.