Omnidirectional Flexible Tri-Band Rectenna With Eliminated Matching Circuit for Ambient RF Energy Harvesting

This article proposes an omnidirectional flexible tri-band rectenna for ambient RF energy harvesting. A novel matching method was proposed to achieve direct conjugate matching between the antenna and the diode at three frequencies simultaneously, eliminating the need for an extra matching circuit. This design method not only reduces circuit losses and complexity but also reduces circuit size. Additionally, the rectenna features an omnidirectional radiation pattern, enabling it to capture RF energy from all directions. Furthermore, the rectenna utilizes a flexible substrate, allowing for conformal applications. For demonstration, a rectenna sample operating at 0.915, 2.45, and 3.5 GHz was fabricated with dimensions of 113
$\times$
23 mm. Measurement results indicate that with a load of 1600
$\Omega $
and an input power of
$-$
20 dBm, the rectenna achieves efficiencies of 33.3%, 21.68%, and 15% at 0.915, 2.45, and 3.5 GHz, respectively. The experiment demonstrates that the rectenna maintains consistent performance across different bending radii. This proposed omnidirectional, flexible, and compact rectenna shows great promise for low-power RF energy harvesting applications.