A New Approach to Microwave Rectennas Using Tightly Coupled Antennas

We present the design of a near unity electromagnetic energy harvester using a tightly coupled antenna (TCA) array. Compared with the unit cell of metamaterial surfaces used earlier, the dimension of a TCA unit cell is about five times larger, thus providing simplified channeling networks and cost-effective solutions. The TCA surface contains an array of Vivaldi shape unit cells with a diode at each cell to convert the collected electromagnetic energy to dc power. The dc power from each unit cell is channeled to one single load via series inductors. A sample of a 4\times 4 TCA array was simulated, fabricated, and tested. Numerical simulations showed that the finite array has the potential to achieve a radiation-to-ac power conversion efficiency of 90% and a radiation-to-dc power conversion efficiency of 72%, while laboratory measurements gave a maximum radiation-to-dc power conversion efficiency of approximately 60%.