Broadband High-Efficiency Microwave Rectifier with Nonuniform Transmission-Line Input Matching for Harmonic Backscattering Applications

The second harmonic produced by the nonlinearity of a diode rectifier can be utilised for backscattering communication. A rectifier for this purpose should not suppress the second harmonic, but its emergence should be embraced in the design. With a traditional transmission-line matching network, composed of serial lines and stubs, it becomes difficult to ensure a high power level of the second harmonic. We propose the use of a nonuniform transmission line (NUTL) to resolve this issue. The NUTL allows nearly uncompromised travel of the second harmonic power. Furthermore, it can enhance the bandwidth of a rectifier. A diode rectifier in voltage doubler configuration with a NUTL matching network, enabling the emission of the second harmonic and efficient operation over a broad frequency range is demonstrated. It has a maximum measured power conversion efficiency (PCE) of 76.5 % at 2.5 GHz and 23.9 dBm input power while backscattering 2.8 dBm at the second harmonic and is able to maintain a PCE higher than 60 % from 2 GHz to 2.75 GHz and above 70 % from 2.25 GHz to 2.65 GHz.