Integration of numerical and field-theoretical techniques in the design of single- and multi-band rectennas for micro-power generation

We introduce an integrated design methodology for the optimisation of RF-to-DC conversion efficiency of multi-band rectennas (rectifying antennas), with the aim of harvesting the RF energy available in humanised environments. Existing RF sources can either operate at known frequencies, power budgets, and locations, or can be ubiquitously available at different frequency bands, and with unknown directions of incidence and polarisations. In all cases the RF link power budget may be extremely low. In order to harvest a significant quantity of energy it is thus mandatory to place a very special care in the design of each part of the receiving/storing system. For this purpose the receiving antenna must be optimised together with the rectifying circuit and the load. In our work this is accomplished by a rigorous design tool based on the concurrent use of nonlinear/electromagnetic (EM) CAD tools and EM theory. The effectiveness of the method is demonstrated by comparing the computed and measured performance of single- and multi-band rectennas, both linearly and circularly polarised. Such antennas are designed to harvest RF energy from a variety of cellular and Wi-Fi systems that are normally present in civil environments.