| Summary: | A high-efficiency microwave power transmission (MPT) system based on an inverted class F (<inline-formula> <tex-math notation="LaTeX">$\text{F}^{-1 }$ </tex-math></inline-formula>) rectifier for microwave wireless charging applications is presented in this paper. A left-hand circular polarization (LHCP) transmitting antenna (Tx) is designed based on a modified sequential phase rotation (SPR) divider integrated with a <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> array. The proposed Tx exhibits compact size with LHCP maximum gain of 11.85 dBi at 5.8 GHz. Furthermore, the receiver is composed of an LHCP receiving antenna (Rx) and a microwave <inline-formula> <tex-math notation="LaTeX">$\text{F}^{-1}$ </tex-math></inline-formula> rectifier. To realize the power radiated region of the Tx, an Rx with a wide beamwidth for minimizing distance loss is proposed, which has a 3-dB axial ratio (AR) beamwidth of 165.55° and 175.17° in the <inline-formula> <tex-math notation="LaTeX">$x - z$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$y - z$ </tex-math></inline-formula> planes, respectively. In addition, to improve the RF to DC conversion efficiency (<inline-formula> <tex-math notation="LaTeX">$\eta $ </tex-math></inline-formula>), the class <inline-formula> <tex-math notation="LaTeX">$\text{F}^{-1}$ </tex-math></inline-formula> harmonic processing network is utilized at the load of the rectifier that can process the voltage and current waveforms without using a DC pass filter. The proposed <inline-formula> <tex-math notation="LaTeX">$\text{F}^{-1}$ </tex-math></inline-formula> rectifier circuit occupies a compact area of <inline-formula> <tex-math notation="LaTeX">$15.3\times12.7$ </tex-math></inline-formula> mm<sup>2</sup>, and it exhibits an average <inline-formula> <tex-math notation="LaTeX">$\eta $ </tex-math></inline-formula> of 50% for the input power range from 4 to 20 dBm with a peak efficiency of 77.9% at 18 dBm. Overall, the experimental results show that our proposed system achieves a maximum power transmission efficiency (PTE) of 8.8% for wirelessly charging low-power multiple devices at a distance of 60–200 mm.
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