Aperture Sharing Metasurface-Based Wide-Beam Antenna for Energy Harvesting

Since the available ambient power level is usually quite low for radio frequency energy harvesting, it is very desirable for an antenna to have both a high gain and a wide beamwidth. Usually, they cannot be achieved simultaneously. In order to overcome this limitation, a multi-port antenna using a nonuniform metasurface (MTS) is presented. In this MTS-based antenna, three modes with complementary radiation patterns are excited through one middle and two side aperture-coupled feeding ports. The first mode is the fundamental TM ₁₀ mode with in-phase current distributions on the MTS. It has a broadside directional radiation pattern with a high gain. The second and third modes are symmetrical to each other at a high mode. They have opposite current distributions on two sides of the MTS. These two modes have a directional radiation pattern with a tilted angle. These three modes share the same aperture but are excited by three different feeds. Each feed is connected to a rectifier. By combining direct current (DC) output to a single load, an antenna with a wide beam and a high gain can be effectively achieved, although each mode has the usual limitation of gain and beamwidth. The key advantage of this proposed rectenna is that the unit cells on the MTS layer can be reused to excite different MTS modes with different radiation patterns simultaneously. Thus, a wide beamwidth can be achieved. Three realized beams are oriented at −35°, 0°, and + 35° respectively. By combining the DC output from the three modes, the proposed rectenna has effectively achieved a beamwidth of 114° with a gain ranging from 8 to 9.8 dBi. The RF-to-DC conversion efficiency of the rectifiers is 3%-67% at 2.45 GHz when the input power ranges from −35 to 0 dBm. The proposed MTS antenna with an overall size of λ ₀ × λ ₀ × 0.03 λ ₀ can achieve 12% fractional bandwidth.