A converter for converting a received radio frequency signal into a DC signal for powering a load, the converter comprising: a rectifier arranged to generate, based on the radio frequency signal, the DC signal and one or more harmonics of the radio frequency signal, and to output the DC signal and the one or more harmonics together with a component of the radio frequency signal; a first planar transmission line arranged to guide the received radio frequency signal to the rectifier; and a second planar transmission line arranged to receive from the rectifier the DC signal, the component of the radio frequency signal and the one or more harmonics from the rectifier, and to reflect the one or more harmonics back towards the rectifier; wherein the first planar transmission line is further arranged to reflect back towards the rectifier radio frequency signals from the rectifier that are based on the reflected signals, the converter further comprises a low-pass filter for supplying the DC signal to the load, the low-pass filter comprising an inductor and a third planar transmission line that connects the second transmission line to the inductor, wherein the third planar transmission line and the inductor are arranged to transmit the DC signal and to substantially block the component of the radio frequency signal and the harmonics of the radio frequency signal, and the converter comprises: (i) a first stub connected to the first planar transmission line arranged to reflect, during operation of the converter, a first harmonic of the radio frequency signal back to the rectifier, and being characterised by (ii) a second stub connected to the first planar transmission line arranged to reflect, during operation of the converter, a second harmonic of the radio frequency signal back to the rectifier. a rectifier arranged to generate, based on the radio frequency signal, the DC signal and one or more harmonics of the radio frequency signal, and to output the DC signal and the one or more harmonics together with a component of the radio frequency signal; a first planar transmission line arranged to guide the received radio frequency signal to the rectifier; and a second planar transmission line arranged to receive from the rectifier the DC signal, the component of the radio frequency signal and the one or more harmonics from the rectifier, and to reflect the one or more harmonics back towards the rectifier; wherein the first planar transmission line is further arranged to reflect back towards the rectifier radio frequency signals from the rectifier that are based on the reflected signals, the converter further comprises a low-pass filter for supplying the DC signal to the load, the low-pass filter comprising an inductor and a third planar transmission line that connects the second transmission line to the inductor, wherein the third planar transmission line and the inductor are arranged to transmit the DC signal and to substantially block the component of the radio frequency signal and the harmonics of the radio frequency signal, and the converter comprises: (i) a first stub connected to the first planar transmission line arranged to reflect, during operation of the converter, a first harmonic of the radio frequency signal back to the rectifier, and being characterised by (ii) a second stub connected to the first planar transmission line arranged to reflect, during operation of the converter, a second harmonic of the radio frequency signal back to the rectifier. (i) a first stub connected to the first planar transmission line arranged to reflect, during operation of the converter, a first harmonic of the radio frequency signal back to the rectifier, and being characterised by (ii) a second stub connected to the first planar transmission line arranged to reflect, during operation of the converter, a second harmonic of the radio frequency signal back to the rectifier.