Design of a Second Harmonic Reradiating Rectenna Using Harmonic Source Pull

This study proposes a design method for rectennas that provide high RF–dc conversion efficiency and enhanced second harmonic reradiation levels by employing source-pull simulation with harmonics. Reusing a harmonic generated by a rectenna is an advantageous retrodirective system, because harmonic reradiation can be used as a battery-less pilot signal. In this retrodirective system, it is essential to ensure that a rectenna effectively reradiates harmonics with high RF–dc conversion efficiency. The proposed design method allows a rectenna to effectively facilitate second harmonic reradiation without additional filters. The source-pull simulation was conducted on a single-series rectifier circuit, revealing the correlation between the RF–dc conversion efficiency and the second harmonic reradiation level, with specific source impedance values at each harmonic. An inverted-F antenna with a short-circuit stub on the back side was designed based on the source-pull simulation results. The designed rectenna has an RF–dc conversion efficiency of 60.6% and a second harmonic reradiation level of 0.17 dBm at a frequency of 920 MHz, with an input power of 10.0 dBm and a load resistance of 1.0 kΩ. This design performs much better than previous designs regarding the harmonic reradiation level while maintaining a high RF–dc conversion efficiency.