A system comprising: a first transceiver that transmits and receives microwave signals at a first frequency, the first transceiver including a midfield coupler that converts signals from the first transceiver to signals with a non-negligible H-field component parallel to a surface of the midfield coupler and focuses the converted signals to a location within tissue that is within a wavelength, as measured in air, of the microwave signals; and an at least partially implantable biocompatible device comprising a second transceiver, the second transceiver including an E-field based antenna that receives the signals from the midfield coupler and characterised in that the second transceiver transmits signals at about the same frequency as the first transceiver, wherein the first transceiver further comprises an amplitude matching network comprising an amplitude detector and a variable gain amplifier electrically coupled to the midfield coupler, the amplitude detector determines an amplitude of a signal received from the second transceiver and the variable gain amplifier adjusts an amplitude of a signal to be provided to the midfield coupler based on the amplitude of the signal received from the second transceiver, wherein the midfield coupler includes two or more ports, wherein the amplitude detector is one of two or more amplitude detectors (3206A-D), each amplitude detector (3206A-D) of the two or more amplitude detectors (3206A-D) electrically coupled to a respective port of the midfield coupler, wherein the first transceiver further comprises a power divider which receives a radio frequency signal and divides and separates the RF signal into two or more signals, one signal for each port of the midfield coupler, and wherein the variable gain amplifier is one of a plurality of variable gain amplifiers (3208A-D), each variable gain amplifier (3208A-D) is electrically coupled between a respective port of the midfield coupler and the power divider, each amplifier (3208A-D) receives a signal of the two or more signals from the power divider and amplifies the signal by a gain, wherein the gain is determined based on an amplitude determined by the amplitude detector (3206A-D) coupled to the same respective of the midfield coupler. a first transceiver that transmits and receives microwave signals at a first frequency, the first transceiver including a midfield coupler that converts signals from the first transceiver to signals with a non-negligible H-field component parallel to a surface of the midfield coupler and focuses the converted signals to a location within tissue that is within a wavelength, as measured in air, of the microwave signals; and an at least partially implantable biocompatible device comprising a second transceiver, the second transceiver including an E-field based antenna that receives the signals from the midfield coupler and characterised in that the second transceiver transmits signals at about the same frequency as the first transceiver, wherein the first transceiver further comprises an amplitude matching network comprising an amplitude detector and a variable gain amplifier electrically coupled to the midfield coupler, the amplitude detector determines an amplitude of a signal received from the second transceiver and the variable gain amplifier adjusts an amplitude of a signal to be provided to the midfield coupler based on the amplitude of the signal received from the second transceiver, wherein the midfield coupler includes two or more ports, wherein the amplitude detector is one of two or more amplitude detectors (3206A-D), each amplitude detector (3206A-D) of the two or more amplitude detectors (3206A-D) electrically coupled to a respective port of the midfield coupler, wherein the first transceiver further comprises a power divider which receives a radio frequency signal and divides and separates the RF signal into two or more signals, one signal for each port of the midfield coupler, and wherein the variable gain amplifier is one of a plurality of variable gain amplifiers (3208A-D), each variable gain amplifier (3208A-D) is electrically coupled between a respective port of the midfield coupler and the power divider, each amplifier (3208A-D) receives a signal of the two or more signals from the power divider and amplifies the signal by a gain, wherein the gain is determined based on an amplitude determined by the amplitude detector (3206A-D) coupled to the same respective of the midfield coupler.