High-Efficiency Microwave Rectifier With Coupled Transmission Line for Low-Power Energy Harvesting and Wireless Power Transmission

In this article, a Schottky diode-based microwave rectifier that employs coupled transmission lines (CTLs) is proposed. CTL is herein used to enhance the voltage amplitude across the Schottky diode with the consequent increase in the rectifier efficiency, especially for low input powers. It is also shown that multiple cascaded CTLs can further enhance the rectifier conversion efficiency, even if this benefit is partially annihilated by the increased insertion loss. Several compact prototypes with single and dual CTLs for 2.45 GHz have been fabricated and measured for different input power levels. Particularly, a single CTL rectifier exhibits RF-to-dc conversion efficiency of 67.7% for an input power of 0 dBm, leading to an improvement of about 3% with respect to other referred rectifiers (with a dc load of 4.47 kQ), while dual CTL rectifier has an outstanding efficiency of 75.3% for an input power of only 5.5 dBm (with a dc load of 1.76 kQ). Passive voltage boost by means of CTLs can be applied to other rectifier circuits as also demonstrated.