Synthesis of Ultra-Wideband Rectenna for RF Energy Harvesting from Wireless Communications Networks.

The continuous development of IoT technologies, and especially of the sensor networks involved with it, brings about an increase in the demand for power self-reliance of the relevant devices, the number of which is expected to be huge Perhaps the most popular and low-cost way for the achievement of this self-reliance, is the utilization of RF(Radio-Frequency) energy that exists in the ambient and the method developed for this purpose is termed as RF energy harvesting.The present work aimed at designing an RF energy harvesting system, referred to by the well-known term "rectenna", being capable of collecting power at 1.8GHz(GSM), 2.1GHz(UMTS), 2.4GHz(Wi-Fi) and 2.6GHz(LTE). Rectennas are mainly consist of an antenna that collects RF ambient energy, a matching network (MN) and a rectifier that converts the collected signal power from AC to DC. Thus, the research focused at first on the synthesis of a novel antenna of wideband type operating effectively at least within the aforementioned bands. Then, various voltage doubling rectifiers were designed, as simple ones or of Greinacher type. MNs, composed of LC circuit elements or microstrip stubs, suitable for matching the designed antenna with the rectifiers, have been also deigned and are presented. The optimum rectifing circuit was found to give DC voltage equal to 3.7 Volts for input power 0dBm. Research on the effectiveness of the designed novel rectennas to harvest ambient RF energy, was also made. Indicatively, a rectenna consisting of the designed antenna, a classic voltage doubling rectifier and a miscrostrip stub, as MN, is presented. It was found, through simulations and considering that plane waves having electric field strength of 1Volt/m(amplitude), incident on the rectenna and coming from 85 different Directions of Arrival (DoAs) could give DC voltage reaching potentially at 0.51Volts. Analytical results and statistical analysis are presented in the paper.