Efficiency of DC Combination of Rectified Waveforms in Energy Harvesting Systems

Rectifier efficiency is one of the dominant factors of the overall efficiency of an energy harvesting system. The nonlinear nature of the rectifying process hinders the development of optimized circuits for maximum efficiency. This has provided the incentive for researchers to use a different approach for increasing the efficiency of the rectennas. The approach consists of interconnection of multiple rectified signals at the direct current (DC) level through serial, parallel or cascaded connections in multiple antenna receivers. Successful experiments have already been conducted and shown the superiority of the cascaded combination in terms of both efficiency and output voltage at the receiver side, when there are only two rectennas to be combined. In this paper, we aim to formulate and recast this design problem in analytical form for the general case when there are K rectennas in the energy harvesting system. The superiority of the cascaded technique is validated through analysis and comparison of the three combination techniques in terms of efficiency, produced DC voltage and output DC current.