A circuit matches the load impedance of an electronic device. The circuit comprises an impedance network, a control circuit suitable for varying the impedance of said network and a sensor coupled with said network and said load and suitable for detecting the ratio between the incident and reflected standing waves in transferring power from the electronic device to the load; the sensor is suitable for providing two signals substantially proportional to the incident and reflected amplitude of the waves at the control circuit. The impedance network is a network of variable resistances and the control circuit is suitable for varying the value of the resistances to lower said ratio between the incident and reflected standing waves to a value that ensures the transfer of power from the electronic device to the load.