A Compact RF Energy Harvesting System With an Improved Impedance Matching Network

This letter presents a compact RF energy harvesting (RFEH) system with an improved impedance matching network. The antenna includes a matching network consisting of periodic stubs, making it possible not only to adjust <inline-formula><tex-math notation="LaTeX">$S_{11}$</tex-math></inline-formula> when it changed due to fabrication errors but also to design the antenna to be more compact. We initially analyzed the effects of the fabrication errors and variations of <inline-formula><tex-math notation="LaTeX">$S_{11}$</tex-math></inline-formula> with respect to an adjustment of the matching network using an EM simulation. The antenna dimensions overall are 14.5 × 18.5 <inline-formula><tex-math notation="LaTeX">$\text{mm}^{\text{2}}$</tex-math></inline-formula>, and it is integrated with an RFEH circuit consisting of a rectifier and power management unit, which compose the RFEH system. The proposed system was implemented, charging a load capacitor at the received power of −15 and −5 dBm; therefore, the proposed system with the impedance matching network contributes to compactness and can be utilized as the power source for compact Internet of Things sensors.