Multiport Rectennas for Ambient RF Energy Harvesting

We describe techniques for using multiport antennas in rectennas suitable for ambient RF energy harvesting. Two antenna combining approaches, RF and dc combining, are briefly reviewed. Four impedance matching techniques, MCM, SOM, MLM, and SPM are also reviewed to show how impedance matching can compensate for the negative impact of mutual coupling in compact multiple antenna systems. Making use of these results three multiport rectenna design examples are also provided to show the benefit of using multiport rectenna to increase harvested RF energy. Using this multiport rectenna approach harvested ambient RF energy can exceed 10 μW in some environments, making them suitable for low power Internet of Things devices.