Compact Circularly Polarized Rectenna With Unbalanced Circular Slots

A novel rectifying antenna (rectenna) using a compact circularly polarized (CP) patch antenna with RF-to-DC power conversion part at 2.45 GHz is introduced, in which the unbalanced slots structure is adopted for size reduction and 2nd harmonic rejection. To contribute a rectenna for RF power conversion, the back side of the CP antenna is the doubler rectifier circuit with 3rd order harmonic rejection radial stub for efficiency optimization and harmonic power re-radiation elimination. The adopted CP antenna built on low cost FR-4 substrate has measured bandwidth of 137 MHz (10 dB return loss) as well as 30 MHz CP bandwidth (3 dB axial ratio). By up to 3rd order harmonic rejection, the RF-to-DC conversion efficiency would reach 53% and 75% with 1 K Omega resistor load under ANSI/IEEE uncontrolled and controlled RF human exposure limit respectively.