High-efficiency microstrip rectenna for microwave power transmission at Ka band with low cost

This paper presents the design and implementation of a high-efficiency microstrip rectenna for millimetre wave power transmission (MMPT) at Ka band with low cost. An experimental method is suggested to obtain the input impedance of the rectifying diode at millimetre-wave bands. So the high-efficiency rectifying circuit could be designed with an effective input impedance match network and two output class-F dc-pass filters. A high-gain Fabry-Perot resonator antenna with circularly polarised (CP) operation and harmonic suppression function is proposed as the receiving antenna, which has a measured 3-dB axial-ratio bandwidth of 6.5% and peak gain of 17 dBi at the centre frequency of 35 GHz. The antenna is fed by a microstrip line, which is the same as the input port of the rectifying circuit, so the integration of the rectenna is easy. The millimetre wave to direct current (MMW-DC) efficiency of the rectenna has been measured in far field, which shows a good CP performance. A more precise measurement system, which could be applied both in near and far fields, is proposed to evaluate the rectenna efficiency. The highest efficiency of 63.8% is measured on the load of 430 at 34.8 GHz with the received power being 77.3 mW.