Mutual coupling effect on rectenna array for RF energy harvesting

A 3×3 rectenna array for ambient RF energy harvesting was studied in terms of antenna element spacing and antenna type. The antenna types considered were a half-wavelength dipole and a loop antenna. To take into account the mutual coupling between antenna elements, the active element patterns for all the elements were calculated. Then, the patterns were used to estimate the combined DC power using non-linear RF-to-DC conversion efficiency. As a result, the obtainable DC power was highly dependent on the receiving angle even when using an omni-directional dipole due to the mutual coupling. The largest DC power was obtained in the array broadside directions when the element spacing was 0.7 or 0.8 wavelengths for both dipole and loop antennas. However, in the scenario considered, to maintain a DC power of 5 dBμW or more from arbitrary receiving directions, the dipole element with the element spacing of 0.8 wavelengths or more was preferable.