Electrically Small Huygens Dipole Rectennas for Wirelessly Powering Internet-of-Things Sensors

Linearly-polarized (LP) and circularly-polarized (CP) electrically small Huygens dipole rectennas for wirelessly powering compact Internet-of-Things (IoT) sensors at 915 MHz in the ISM band are reported. They are realized through the seamless integration of electrically small near-field resonant parasitic-based Huygens LP and CP antennas with a highly efficient rectifier circuit. The Huygens LP (HLP) antenna achieves a cardioid-shaped realized gain (RG) pattern with RG=3.8 dBi at the targeted frequency. Similarly the Huygens CP (HCP) antenna generates a cardioid pattern with RG=3.2 dBic and a 1.7 dB axial ratio value. Notably, the HLP and HCP antennas have inductive input impedances that facilitate matching directly to the 50-Omega source, thus eliminating a lossy inductor in the original rectifier. The prototyped HLP and HCP rectennas achieve close to 90% AC to DC conversion efficiency. Light and temperature IoT sensors wirelessly powered with custom-designed versions of these rectennas are successfully demonstrated.