Rectennas for wide range RF power harvesting -

Abstract

Wireless communication applications fill up our ambient environment with electromagnetic waves (EM) carrying energy at different frequencies. The RF energy harvesting process relies on these EM waves in order to rectify them into DC power. This process can be directed towards the charging of battery dependent devices such as mobile devices or distant sensor networks. Such technique is the basis of what is now known as wireless charging from RF energy and constitutes a great advantage for any mobile or distant device. Many factors affect the design process of any RF harvesting circuit. The appropriate high-frequency impedance matching and the transmission line effects must be taken into account during the design stage in addition to the nonlinear effects of the incorporated rectifying diodes. The Schottky rectifying diodes are mainly capable of efficiently converting the RF energy into DC under specific conditions of the received power. At very low power levels, the forward voltage effect limits the conversion efficiency of the overall circuit. On the other hand, as the received power increases the diode enters into breakdown which causes the generated DC power to saturate and hence the efficiency to drop exponentially. In this thesis, the aim is to design a new RF circuit with enhanced operable power range over which rectification can be efficiently performed. The objective is to find a solution to the breakdown problem that is inherent in the nature of diodes. The investigation process is based on understanding the inadequacy of using the well-known PN junction diode at microwave frequencies, deciphering RF rectification, and incorporating all the gathered information to design the new rectifying system that is able to cater for a wider range of power levels at a practical frequency of operation. Various rectifying circuits and rectenna systems are developed, tested and compared. These systems are able to harvest and rectify the RF signal at an acceptable efficiency for a wide power range. The measured desig