Integrated Coupler-Antenna Design for Multibeam Dual-Polarized Patch-Array Rectenna

The multibeam antenna can facilitate effective harvesting of RF energy with low power densities, different polarizations, and different incident directions. The use of coupler-based beamforming circuit in the array antenna is a common implementation method. The inevitable coupling between antenna elements is usually an obstacle to compactness due to the separate design of antenna and circuit. In this article, a scheme is proposed to integrate two coupled patches and two hybrid couplers. It exploits the unfavorable coupling in conventional designs and can reduce both the spacing between antenna elements and the redundant circuit of hybrid coupler. A compact four-beam rectenna is then presented with high gains and dual polarizations in enhanced spatial coverage. The complex $J$ inverter, instead of commonly used real one, is introduced to characterize the coupling and reflect its effect on excitation of antennas. With an optimized four-branch rectifier circuit corresponding to the four beams, the rectenna demonstrates a maximum dc power of 54.1– $66.3~\mu \text{W}$ , a maximum RF-to-dc efficiency of 44.3%–52.3%, and a minimum dc power of 24.5– $28.7~\mu \text{W}$ in an azimuth angle range of 90° when the incident RF power is with different linear polarizations and a density of $1~\mu \text{W}$ /cm².