Design of Wearable Rectennas Harvesting from Multi-Tone Ambient RF sources

In this paper we describe the design and test of a wearable, multi-band ring-antenna together with its rectifying circuit. The system is required to harvest RF energy from GSM 900, GSM 1800 and WiFi sources available in the ambient. A annular ring topology is selected for the antenna to be printed on textile and flexible substrates and is suitable modified with appropriate slots to cover the bands of interest. A multilayer configuration is exploited for wearable purposes and related integration issues are discussed. Due to the scarce amount of available energy, the primary goal in designing the antenna is to achieve high radiation efficiency and circular polarization in compact dimensions, compatible with technology garments. A rectenna is then designed by the concurrent use of harmonic-balance technique and electromagnetic simulation to predict the real rectified power in general operating conditions.