A Compact Rectenna With Flat-Top Angular Coverage for RF Energy Harvesting

The efficiency of rectifying antennas (rectennas) always suffers when the energy sources change with space and time and have low incident power density in the harvesting of radio frequency (RF) energy. This letter presents a novel rectenna design which consists of a receiving antenna array insensitive to the location of the energy source and a rectifier suitable for the low incident power conditions. The design of the receiving array is based on the method of maximum power transmission efficiency expressed in the form of quadratically constrained quadratic programing. The receiving antenna features a flat-top beam collection range whose angular coverage is adjustable depending on the applications. The SMS 7630 diode is selected and mounted on the rectifier for the enhancement of rectification efficiency when the incident power is low. To validate the design method, a six-element patch receiving array with less than half-wavelength interelement spacing and a rectifier operating at 5.8 GHz industrial, scientific, and medical (ISM) band are fabricated, and the overall rectification performance is tested. The measurement results indicate that the value of output dc voltage remains almost unchanged when the energy source moves within the range from -45° to +45° in the H-plane under the identical distance.