Rigorous Design of RF Multi-Resonator Power Harvesters

In this paper an integrated design methodology to predict the real RF to DC conversion capability of power harvesters is tackled. By combining nonlinear harmonic-balance-based analysis with electromagnetic simulation the method is able to compute the actual RF power at the rectifier input in general operating conditions: that is for any near-field /far-field behavior of the antenna and for any direction of incidence and polarization of the incoming RF wave. This approach makes use of a new definition of the rectifying antenna (rectenna) performance simultaneously accounting for its radiation and nonlinear behavior. The effectiveness of the method is demonstrated through the comparison between computed and experimental performance of a multi-band circularly polarized rectenna, both in rigid and wearable implementation. Such antennas have been designed to harvest RF energy from different wireless standards (GSM 900, GSM 1800 and WiFi), commonly present in civil environments.